温度对水稻花粉发育的影响

Heat stress during the flowering stage induces a remarkable decrease in rice spikelet fertility, mainly due to poor pollination manifesting as insufficient pollen deposited on the stigma. It is hypothesized that stigma exsertion, which confers a pollination advantage, may enhance pollen reception and improve female reproductive success under heat stress. The present study aimed to investigate the role of stigma exsertion in spikelet fertility under nocturnal heat. Four rice cultivars exhibiting distinct heat tolerance and twenty rice cultivars with varying degrees of stigma exsertion were grown and subjected to high nighttime temperature treatment at anthesis, in 2023 and 2019, respectively. Heat-tolerant rice cultivars had a relatively low percentage of spikelets with exserted stigmas, and vice versa. Under nocturnal heat stress, rice cultivars exhibiting higher stigma exsertion showed significantly greater reductions in spikelet fertility compared to lower stigma exsertion cultivars. The spikelet fertility of rice cultivars with a higher degree of stigma exsertion was reduced more seriously than that of cultivars with a lower degree of stigma exsertion. Rice spikelet fertility positively correlated with the percentage of hidden stigmas, and exogenous substance-induced increased stigma exsertion led to reduced spikelet fertility under nocturnal heat. These results indicate that a hidden stigma contributes to higher spikelet fertility, while increased stigma exsertion aggravates spikelet sterility in rice cultivars under nocturnal heat conditions. It is proposed that hidden stigmas could serve as a novel breeding trait for sustaining rice spikelet fertility against nocturnal heat stress.

Rice is one of the most valuable staple food crops in the world. However, several challenges greatly affect production, one of which is the threat imposed by heat stress. To address this, researchers are developing varieties that are heat stress tolerant with genetic markers aid. In this study, eight rice genotypes, namely Dular, Nagina 22, NSIC Rc 222, Milyang 23, EL15, EL92, EL85, and IR52 were observed for agromorphic data, which included plant height, panicle length, filled and unfilled grains, and grain yield. Flower samples were collected to determine the effect of heat stress on pollen fertility. Molecular markers were designed via in silico analysis based on the nine QTL regions distributed among five chromosomes (1, 3, 4, 5, and 10). Out of the 90 newly developed markers, Markers 3066 and 2503 showed good potential as informative markers among heat tolerance classification. Results showed the genotype-specific responses of varieties during heat stress and non-heat stress conditions. EL15 had the best agromorphic performance and appeared to be the best elite line. Identification of gene-specific SSR markers has proven to be effective in understanding heat tolerance for future marker-assisted selection.

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Low phytic acid (lpa) crop is considered as an effective strategy to improve crop nutritional quality, but a substantial decrease in phytic acid (PA) usually has negative effect on agronomic performance and its response to environment adversities. Myo-inositol-3-phosphate synthase (MIPS) is the rate-limiting enzyme in PA biosynthesis pathway, and regarded as the prime target for engineering lpa crop. In this paper, the rice MIPS gene (RINO2) knockout mutants and its wild type were performed to investigate the genotype-dependent alteration in the heat injury-induced spikelet fertility and its underlying mechanism for rice plants being imposed to heat stress at anthesis. Results indicated that RINO2 knockout significantly enhanced the susceptibility of rice spikelet fertility to heat injury, due to the severely exacerbated obstacles in pollen germination and pollen tube growth in pistil for RINO2 knockout under high temperature (HT) at anthesis. The loss of RINO2 function caused a marked reduction in inositol and phosphatidylinositol derivative concentrations in the HT-stressed pollen grains, which resulted in the strikingly lower content of phosphatidylinositol 4,5-diphosphate (PI (4,5) P2) in germinating pollen grain and pollen tube. The insufficient supply of PI (4,5) P2 in the HT-stressed pollen grains disrupted normal Ca2+ gradient in the apical region of pollen tubes and actin filament cytoskeleton in growing pollen tubes. The severely repressed biosynthesis of PI (4,5) P2 was among the regulatory switch steps leading to the impaired pollen germination and deformed pollen tube growth for the HT-stressed pollens of RINO2 knockout mutants.

Drought and heat stress at flowering stage affect rice yield. Hence, it is very important to understand the thermal changes of rice canopy during drought and heat stress conditions. Thus, objective of this study was to assess the thermal changes inside the canopy and its impact on pollen fertility and yield. A split plot design with three replicates was used for the field experiments at Field Crops Research and Development Institute, Mahailluppallama in three Yala seasons from Yala 2014 to Yala 2016. Main factor was the planting time (early and late planting) which synchronizes flowering at different temperature regimes. Sub-plots were Bg 358 flooded, Bg 358 drought stress, Bg 366 flooded and Bg 366 drought stress. Data were collected on ambient temperature, relative humidity, canopy temperature, volumetric moisture content of soil, pollen fertility and grain yield. The lowest canopy temperature was observed in early planting flood treatments. Maintaining volumetric moisture content at 27.5% with a canopy temperature of 300C resulted in 90% pollen fertility. Peak canopy temperature and canopy temperature at flower opening was highly correlated with grain yield. Peak canopy temperature and canopy temperature at 10:00 augmented the rice yield. The critical canopy temperature on yield was estimated as 340C. Maintenance of standing water at flowering stage is an important migratory option to avoid heat stress in rice.

Rice cultivated under rainfed or semi-irrigated ecosystems is frequently exposed to a combination of drought and heat stress. As a sensitive crop at the reproductive stage, exposure to combined drought and heat stress will have a deleterious effect on yield. In this study, two rice cultivars with contrasting spikelet sterility, AVT2-5315 (low sterility) and AC35027 (high sterility), under combined stress were selected for physiological characterization and phytohormonal profiling at anthesis. Under combined stress, both cultivars did not differ in the physiological parameters such as relative water content, photosynthetic rate, light-adapted chlorophyll fluorescence and biomass, suggesting a similar source activity under stress. However, AVT2-5315 showed better yield due to better pollen and spikelet fertility than AC35027, suggesting its intrinsic tolerance ability under combined stress. Targeted profiling of 15 phytohormones from drought, heat and combined stress-treated flag leaf and spikelet tissues using LC–MS/MS showed increased accumulation of auxins (indole 3-acetic acid and indole 3-butyric acid) in flag leaves and jasmonic acid in spikelets of AVT2-5315, while there was increased accumulation of ethylene in flag leaves and methyl-jasmonate in spikelets of AC35027. Increased accumulation of these hormones correlated with key biosynthetic pathway genes. In the flag leaves, increased accumulation of auxins was correlated with increased transcript levels of YUCCA-like gene 1 (OsYUCCA1) and fish bone (OsFIB), in AVT2-5315 under combined stress. In AC35027, increased ethylene content was correlated with expression of 1-aminocyclopropane-1-carboxylate synthase 1 (OsASC1) and aminocyclopropane-1-carboxylic acid oxidase 2 (OsACO2). Similarly, in spikelets, increased accumulation of jasmonic acid in AVT2-5315 was correlated with expression of allene oxide cyclase (OsAOC) and 12-oxophytodienoic acid reductase 1 (OsOPR1). The mechanism of regulating spikelet sterility by these hormones needs further investigation towards improving rice tolerance to combined stress.

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The damage caused by high temperature is one of the most important abiotic stress affecting rice production. Reproductive stage of rice is highly susceptible to high temperature. The present investigation was undertaken to identify polymorphic microsatellite markers (SSR) associated with heat tolerance. The rice cultivars NERICA– L 44 (heat tolerant) and Uma (heat susceptible) were crossed to generate F1 and F2 populations. The F2 population was subjected to heat stress at >38°C and the 144 F2 plants were evaluated for their tolerance. The results note that the mean of the F2 population was influenced by the tolerant parent with regards to the traits of plant height, membrane stability index, photosynthetic rate, stomatal conductance, evapotranspiration rate, pollen viability, spikelet fertility and 1000 grain weight. Ten each of the extremely susceptible and tolerant plants were selected based on the spikelet fertility percentage. Their DNA was pooled into tolerant and susceptible bulks and Bulked Segregant Analysis (BSA) was carried out using 100 SSR markers to check for polymorphism. The survey revealed a polymorphism of 18% between the parents. RM337, RM10793, RM242, RM5749, RM6100, RM490, RM470, RM473, RM222 and RM556 are some of the prominent markers that were found to be polymorphic between the parents and the bulks. We performed gene annotation and enrichment analysis of identified polymorphic markers. Result revealed that the sequence specific site of that chromosome mostly enriched with biological processes like metabolic pathway, molecular mechanism, and subcellular function. Among that RM337 was newly reported marker for heat tolerance. Expression analysis of two genes corresponds to RM337 revealed that LOP1 (LOC_Os08g01330) was linked to high temperature tolerance in rice. The results demonstrate that BSA using SSR markers is useful in identifying genomic regions that contribute to thermotolerance.

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The reproductive stage of rice is vulnerable to heat stress, which reduces spikelet fertility and yield. Auxin significantly influences reproductive development, hence the research aimed to enhance spikelet fertility and grain attributes in rice plants by exploring the application efficiency of Indole-3-acetic acid (IAA) and 1-naphthaleneacetic acid (NAA) under heat stress. This study investigated the effects of IAA (10 μmol L−1) and NAA (100 μmol L−1) on spikelet fertility rate in six rice genotypes during the flowering stage. Compared to the heat stress (HS) treatment, the spikelet production rate and grain yield per plant were higher by 61.16%, 37.25%, and 33.07%, and 72.84%, 44.48%, and 32.71% in control, HS + NAA, and HS + IAA treatments, respectively. In addition, panicle weight, primary branches number panicle−1, and 1000-grains weight were significantly (p < 0.05) improved with HS + IAA and HS + NAA application under heat stress conditions. Auxin application enhanced photosynthetic and transpiration rate, while contrarily, leaf temperature diminished. The higher photosynthetic rate showed positive relationships with spikelet fertility (r = 0.64) and yield plant−1 (r = 0.63). Additionally, leaf temperature had a strongly negative correlation (r = −0.81) with the spikelet fertility rate. The application of auxin increased the number of filled grains panicle−1, which showed a positive relationship (r = 0.75) with grain yield plant−1. The variation of spikelet fertility rate among genotypes was dependent on the variety tolerance rate. Overall, these findings indicate that exogenous auxin application can mitigate the negative impact of heat stress on rice and improve spikelet fertility and grain yield.

Low-temperature stress (LTS) is a major limiting factor for rice production in high-latitude regions. Many studies have reported the impacts of LTS on leaf photosynthesis and yield, but few of them explored the response of photosynthesis, chloroplast ultrastructure, pollen fertility, cold stress adaptation to LTS at different growth stages of rice. In this study, we conducted a two-year temperature-controlled field experiment (in 2023 and 2024) to investigate the effects of LTS at the tillering, booting, and heading stages on physiological and biochemical characteristics, plant growth, pollen fertility, and grain yield for a japonica rice cultivar (Longgeng31). The results showed that rice photosynthesis gradually decreased as the LTS temperature was decreasing and the LTS duration was increasing. The net photosynthetic rate (Pn) decreased the most at the booting stage, followed by the tillering, and the heading stages. Compared with controlled group (CK), the LTS treatment at 11.5°C for 3–10 days significantly reduced Pn by 52.2% ~ 62.7%, 85.3% ~ 93.9% and 39.3% ~ 44.9%, at the tillering stage, booting and heading stages respectively. Increasing LTS intensity and duration caused distorted chloroplast morphology and reduced plant height. The concentrations of the antioxidant and osmotic regulation systems in rice peaked after 7 days of LTS treatment, indicating that the stress response to LTS showed a trend of initially increasing and subsequently decreasing. The grain yield decreased the most under LTS at the booting stage by 59.30%−88.76% on D10, followed by the heading and tillering stages. After 10 days of exposure to LTS, the pollen viability decreased most significantly at the heading stage by 44.67%, followed by the booting and the tillering stages. These findings could provide a theoretical basis for identifying and evaluating LTS in rice under field conditions, and provide a methodological reference for the identification and monitoring of LTS in other crops, thereby holding significant practical implications.

Extremely high temperatures are becoming an increasingly severe threat to crop yields. It is well documented that salicylic acid (SA) can enhance the stress tolerance of plants; however, its effect on the reproductive organs of rice plants has not been described before. To investigate the mechanism underlying the SA-mediated alleviation of the heat stress damage to rice pollen viability, a susceptible cultivar (Changyou1) was treated with SA at the pollen mother cell (PMC) meiosis stage and then subjected to heat stress of 40 °C for 10 d until 1d before flowering. Under control conditions, no significant difference was found in pollen viability and seed-setting rate in SA treatments. However, under heat stress conditions, SA decreased the accumulation of reactive oxygen species (ROS) in anthers to prevent tapetum programmed cell death (PCD) and degradation. The genes related to tapetum development, such as EAT1 (Eternal Tapetum 1), MIL2 (Microsporeless 2), and DTM1 (Defective Tapetum and Meiocytese 1), were found to be involved in this process. When rice plants were exogenously sprayed with SA or paclobutrazol (PAC, a SA inhibitor) + H2O2 under heat stress, a significantly higher pollen viability was found compared to plants sprayed with H2O, PAC, or SA + dimethylthiourea (DMTU, an H2O2 and OH· scavenger). Additionally, a sharp increase in H2O2 was observed in the SA or PAC+ H2O2 treatment groups compared to other treatments. We suggest that H2O2 may play an important role in mediating SA to prevent pollen abortion caused by heat stress through inhibiting the tapetum PCD.

To elucidate the mechanism underlying the response of rice to heat stress (HS), the transcriptome profile of panicles was comparatively analyzed between the heat-tolerant line 252 (HTL252) and heat-susceptible line 082 (HSL082), two rice recombinant inbred lines (RILs). Our differentially expressed gene (DEG) analysis revealed that the DEGs are mainly associated with protein binding, catalysis, stress response, and cellular process. The MapMan analysis demonstrated that the heat-responsive (HR) genes for heat shock proteins, transcription factors, development, and phytohormones are specifically induced in HTL252 under HS. Based on the DEG analysis, the key gene OsNCED1 (Os02g0704000), which was induced under HS, was selected for further functional validation. Moreover, 9-cis-epoxycarotenoid dioxygenase (NCED) is a key rate-limiting enzyme in the ABA biosynthetic pathway. Overexpression of OsNCED1 improved the HS tolerance of rice at the heading and flowering stage. OsNCED1-overexpression plants exhibited significant increases in pollen viability, seed setting rate, superoxide dismutase (SOD) and peroxidase (POD) activities, while significantly lower electrolyte leakage and malondialdehyde (MDA) content relative to the wild type (WT). These results suggested that OsNCED1 overexpression can improve the heat tolerance of rice by enhancing the antioxidant capacity. Overall, this study lays a foundation for revealing the molecular regulatory mechanism underlying the response of rice to prolonged HS.

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Temperature rise predicted for the future will severely affect rice productivity because the crop is highly sensitive to heat stress at the reproductive stage. Breeding tolerant varieties is an economically viable option to combat heat stress, for which the knowledge of target genomic regions associated with the reproductive stage heat stress tolerance (RSHT) is essential. A set of 192 rice genotypes of diverse origins were evaluated under natural field conditions through staggered sowings for RSHT using two surrogate traits, spikelet fertility and grain yield, which showed significant reduction under heat stress. These genotypes were genotyped using a 50 k SNP array, and the association analysis identified 10 quantitative trait nucleotides (QTNs) for grain yield, of which one QTN (qHTGY8.1) was consistent across the different models used. Only two out of 10 MTAs coincided with the previously reported QTLs, making them novel. A total of 22 QTNs were observed for spikelet fertility, among which qHTSF5.1 was consistently found across three models. Of the QTNs identified, seven coincided with previous reports, while the remaining QTNs were new. The genes near the QTNs were found associated with the protein–protein interaction, protein ubiquitination, stress signal transduction, and so forth, qualifying them to be putative for RSHT. An in silico expression analysis revealed the predominant expression of genes identified for spikelet fertility in reproductive organs. Further validation of the biological relevance of QTNs in conferring heat stress tolerance will enable their utilization in improving the reproductive stage heat stress tolerance in rice.

Introduction Rice productivity is severely hampered by heat stress (HS) which induces oxidative stress in this crop. This oxidative stress can be alleviated using various exogenous chemicals, including spermidine (Spd). Therefore, the present study was carried out to characterize HS components and to elucidate the role of exogenous Spd application in rice at the flowering stage. Methods Two contrasting rice genotypes, i.e. Nagina22 (N22) and Pusa Basmati-1121 (PB-1121) were placed in temperature tunnels and exposed to HS (38–43°C) with and without Spd (1.5 mM) foliar application during the heading stage till the end of the anthesis stage. Result Heat stress induced the production of H2O2 and thiobarbituric acid reactive substances, which resulted in lower photosynthesis, spikelet sterility, and reduced grain yield. Interestingly, foliar application of Spd induced antioxidant enzyme activities and thus increased total antioxidant capacity resulting in higher photosynthesis, spikelet fertility, and improved grain yield under HS in both genotypes. Under HS with Spd, higher sugar content was recorded as compared to HS alone, which maintained the osmotic equilibrium in leaf and spikelets. Spd application initiated in vivo polyamine biosynthesis, which increased endogenous polyamine levels. Discussion This study corroborates that the exogenous application of Spd is promising in induction of antioxidant defence and ameliorating HS tolerance in rice via improved photosynthesis and transpiration. Thereby, the study proposes the potential application of Spd to reduce HS in rice under current global warming scenario.

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: Stress from high temperatures is one of the factors that restrict rice plant growth and development. Rice generative stage sensitivity to high temperatures is well established, but its vegetative stage sensitivity is more uncertain. To identify high-temperature tolerance traits in the vegetative and generative stages, four local upland rice genotypes were tested under high-temperature stress treatment (32-36°C) during the vegetative stage, generative stage and vegetative-generative stage and ambient temperature (27-31°C) during the vegetative-generative stage as a control. The research used a nested randomized block design (RAK) and was repeated in 3 repetitions. SPSS Ver. 20 program was used to analyze the data. The results showed that under stress from high temperature both thegenerative stage and the vegetative-generative stage significantly reduced the quantity of pollen germinated in all genotypes. The application of under stress from the high temperature in the generative stage showed a serious impact on panicle length, spikelets in each panicle, spikelet fertility in each panicle, weight of filled grain in each panicle, weight of 1000 grains and reduction in amylose compared to theunder stress from high temperature both in the vegetative and vegetative-generative stages. In contrast to previous research, the impact of high temperatures in the vegetative stage was able to significantly increase the length of the panicle, quantity of spikelets in each panicle, spikelet fertility in each panicle, weight of filled grain in each panicle and weight of 1000 grains. The Bangkok genotype has a quantity of pollen germinated of 61.21-44.64%, spikelet fertility in each panicle of 74.91-215.52 grains andweight of filled grain in each panicle of 1.43-4.88 g higher as well as a decrease in amylose and an increase in protein lower than the other three genotypes at high-temperature stress at various stage stages, the Bengkok genotype is a potential genetic source for increasing tolerance to under stress from high temperature in the vegetative and generative stages.

Abstract High-temperature events are projected to increase in frequency under future climate scenarios, threatening rice yields globally. This study investigated the physiological and molecular responses of two Brazilian flooded rice varieties, IRGA 428 and BR-IRGA 409, during the anthesis stage under high-temperature stress, aiming to uncover mechanisms of heat tolerance. Plants were exposed to a daytime temperature of 38°C for 7 h across 3, 5, or 7 days. Prolonged heat stress led to a significant reduction in filled grain in both cultivars, although BR-IRGA 409 demonstrated greater heat tolerance, particularly under 3 days of stress, as it maintained higher spikelet fertility compared to IRGA 428. Comparative transcriptome analysis revealed that BR-IRGA 409 had more differentially expressed genes in response to heat stress, including a significant upregulation of canonical heat-responsive genes such as heat shock factors, heat shock proteins, and peptidyl-prolyl isomerase FK506-binding proteins (FKBPs). Furthermore, BR-IRGA 409 displayed enhanced modulation of the mitochondrial electron transport pathway, which is crucial for adenosine triphosphate (ATP) synthesis and cellular energy production. Interestingly, while photosynthetic performance varied between cultivars, only a few genes associated with photosynthesis were significantly altered in response to heat stress. Instead, BR-IRGA 409 displayed a higher basal expression of photosynthesis-related genes, suggesting that this pre-adaptation might mitigate heat stress impacts on photosynthesis. The ability to preserve functional photosynthetic activity is critical for sustaining the energy-intensive process required to cope with heat stress. This study highlights the difference between the varieties in their response to heat stress and identifies candidate molecular and physiological mechanisms that contribute to maintaining cellular energy homeostasis and heat tolerance in Brazilian rice, providing valuable insights for crop improvement strategies.

Wild species and derived introgression lines (ILs) are a good source of genes for improving complex traits such as heat tolerance. The effect of heat stress on 18 yield traits was studied in four treatments in two seasons, under field conditions by subjecting 37 ILs and recurrent parents Swarna and KMR3, N22 mutants, and wild type and 2 improved rice cultivars to heat stress using polycover house method in wet season and late sowing method in dry season. Normal grown unstressed plants were controls. Both correlation and path coefficient analysis showed that the major contributing traits for high yield per plant (YPP) under heat stress conditions were tiller number, secondary branches in panicle, filled grain number, and percent spikelet fertility. Three ILs, K-377-24, K-16-3, and S-148 which gave the highest YPP of 12.30–32.52 g under heat stress in both the seasons were considered the most heat tolerant. In contrast, K-363-12, S-75, and Vandana which gave the least YPP of 5.36–10.84 g were considered heat susceptible. These lines are a good genetic resource for basic and applied studies on heat tolerance in rice. Genotyping using 49 SSR markers and single marker analysis (SMA) revealed 613 significant marker- trait associations in all four treatments. Significantly, nine markers (RM243, RM517, RM225, RM518, RM525, RM195, RM282, RM489, and RM570) on chromosomes 1, 2, 3, 4, 6, and 8 showed association with six traits (flag leaf spad, flag leaf thickness, vegetative leaf temperature, plant height, panicle number, and tiller number) under heat stress conditions in both wet and dry seasons. Genes such as heat shock protein binding DnaJ, Hsp70, and temperature-induced lipocalin-2 OsTIL-2 close to these markers are candidates for expression studies and evaluation for use in marker assisted selection for heat tolerance.

No abstract available

BACKGROUND In a screening of anilinopurine, anisiflupurin was identified as potent inhibitor of cytokinin dehydrogenase/oxidase (CKX). Inhibitors of CKX have been supposed to be potent plant growth regulators to alleviate the detrimental effects of abiotic stress on crop production. The aim of the study was to profile anisiflupurin in a set of physiological assays and to evaluate its potential for heat stress mitigation in rice field trials. RESULTS Anisiflupurin delayed dark-induced senescence and increased transpiration in detached maize leaves in a dose-dependent manner. Similarly, the transpiration of young rice plants under heat stress was increased for several days after application with anisiflupurin. Application of anisiflupurin during early phases of generative growth not only restored heat-induced pollen alterations it increased grain yield in field grown rice under heat conditions as demonstrated in a large field program conducted in southeast Asia. Thereby, efficacy of anisiflupurin was rate-dependent and most effective when applied during early generative growth phases prior heat stress. CONCLUSIONS Application of anisiflupurin secures seed setting by protecting pollen development and enhances grain weight under heat stress conditions in rice. The results of this research opens up a promising avenue for mitigating the adverse effects of heat stress in rice cultivation. © 2024 Society of Chemical Industry.

Abstract In the present global warming scenario, it is urgent to impart heat tolerance into the popular high yielding rice (Oryza sativa L.) varieties to reduce yield loss to a great extent. Uma (a prevalent red-grained rice variety in Kerala) was crossed with Nagina 22 (N22), the popular donor for heat tolerance. From the seven promising heat-tolerant F3 plants previously identified through marker assisted selection and field screening, F4 lines (58 nos.) were raised and characterised morphologically. Heat tolerance was scored under natural heat stress during hot summer months in field conditions. Among the evaluated F4 progenies, 26 promising plants registered >75% spikelet fertility. Double panicles were observed in some of the tillers of fourteen F4 plants. During the selection with reported polymorphic markers between parents, all the 26 F4 plants produced the corresponding amplicon for RM5749 (linked marker for heat tolerance in the parental cross Uma x N22) and also for RM9, RM201, RM208, RM225, RM242, RM495, RM3586, RM6100, RM6836, and RM26212, corresponding to the heat tolerant parent N22. Genomic analysis revealed 64% recovery of the Uma genome in seven F4 plants, with maximum genomic regions of Uma on the chromosomes 3 and 5. These promising F4 plants could be forwarded to generate stable and high yielding heat tolerant rice varieties. The identified markers could be used for linkage analysis and QTL mapping in future. Keywords: Heat stress; Rice; spikelet fertility; SSR; QTL

In general, the fertility and kernel weight of inferior spikelets of rice (Oryza Sativa L.) are obviously lower than those of superior spikelets, especially under abiotic stress. However, different responses to heat stress are seemed to show between the superior and inferior spikelet, and this response is scarcely documented that the intrinsic factors remain elusive. In order to reveal the mechanism underlying, two rice plants with different heat tolerance were subjected to heat stress of 40°C at anthesis. The results indicated that a greater decrease in fertility and kernel weight was observed in superior spikelets compared to inferior spikelets. This decrease was primarily ascribed to their different organ temperatures, in which the temperature of the superior spikelets was significantly higher than that of inferior spikelets. We inferred the differences in canopy temperature, light intensity and panicle types, were the primary reasons for the temperature difference between superior and inferior spikelets. Under heat stress, the fertility and kernel weight of superior and inferior spikelets decreased as the panicle numbers per plant were reduced, which was accompanied by significantly increasing the canopy temperatures. Thus, it was suggested that the rice plant with characteristic features of an upright growth habit and loose panicles might be more susceptible to heat stress resulting from their higher canopy and spikelets temperatures.

The pollen viability directly affects the pollination process and the ultimate grain yield of rice. Here, we identified that the MORN motif-containing proteins, OsMORN1 and OsMORN2, had a crucial role in maintaining pollen fertility. Compared with the wild type (WT), the pollen viability of the osmorn1 and osmorn2 mutants was reduced, and pollen germination was abnormal, resulting in significantly lower spikelet fertility, seed-setting rate, and grain yield per plant. Further investigation revealed that OsMORN1 was localized to the Golgi apparatus and lipid droplets. Lipids associated with pollen viability underwent alterations in osmorn mutants, such as the diacylglyceride (18:3_18:3) was 5.1-fold higher and digalactosyldiacylglycerol (18:2_18:2) was 5.2-fold lower in osmorn1, while the triacylglycerol (TG) (16:0_18:2_18:3) was 8.3-fold higher and TG (16:0_18:1_18:3) was 8.5-fold lower in osmorn2 than those in WT. Furthermore, the OsMORN1/2 was found to be associated with rice cold tolerance, as osmorn1 and osmorn2 mutants were more sensitive to chilling stress than WT. The mutants displayed increased hydrogen peroxide accumulation, reduced antioxidant enzyme activities, elevated malondialdehyde content, and a significantly decreased seedling survival rate. Lipidomics analysis revealed distinct alterations in lipids under low temperature, highlighting significant changes in TG (18:2_18:3_18:3) and TG (18:4_18:2_18:2) in osmorn1, TG (16:0_18:2_18:2) and PI (17:2_18:3) in osmorn2 compared to the WT. Therefore, it suggested that OsMORN1 and OsMORN2 regulate both pollen viability and cold tolerance through maintaining lipid homeostasis.

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In recent years, the frequency and intensity of exposure to heat stress have increased gradually, seriously hampering the production of maize. This paper presents a study designed to analyze how the development, physiology and dispersal of pollen from the heat‐resistant maize variety Zhengdan958 and the heat‐sensitive maize variety Xianyu335 are affected by exposure to heat stress during the tasselling stage. Our results showed That exposure to heat stress significantly increased the antioxidant enzyme activity in pollen. Upon visual inspection of the pollen, we found that the lower water content had given rise to wrinkles in the pollen surface, sunken germination pores, and morphological deformations. In addition, the anther dehiscence process was hindered, resulting in a reduced amount of pollen being dispersed. We also found elevated levels of abscisic acid (ABA), jasmonic acid (JA) and its derivatives, indole acetic acid (IAA) and gibberellin‐3 (GA3) in heat‐pollens, as well as elevated ratios of IAA to ABA and ABA to GA3. Ultimately impaired pollen fertility. Summarizing, our experiment revealed that reduced pollen quantity and quality are significant contributors to fertility losses in summer maize exposed to heat stress at anthesis, and we hope that our analysis of the physiological mechanisms involved can contribute to the development of crop management measures aimed at countering the increasingly detrimental effects of heat stress on the production of summer maize.

The increased frequency of extreme heat stress events due to climate change is adversely impacting rice yield. Nitrogen (N) is an essential element in the synthesis of chlorophyll in rice, contributing substantially to the achievement of spikelet fertility and addressing the high yields. Two experiments were conducted in Japan and Afghanistan in 2020 and 2022, respectively, utilizing IR64 and Nipponbare (NPB) varieties to elucidate the efficacy of N top-dressing on spikelet fertility and yield of rice under heat stress conditions. In experiment I, the treatments involved were based on N application before panicle emergence in pots, including (1) control (fertilized at the tillering stage), (2) control + N topdressing, (3) heat stress (fertilized at the tillering stage), and (4) heat stress + N topdressing. Experiment II consisted of (1) control (basal dressing at the tillering stage) and (2) control + N topdressing, which was conducted under field conditions. Results showed that N application significantly (p < 0.05) increased SPAD values and spikelet fertility rates in both experiments. A positive correlation (range; r = 0.83–0.98) was observed between enhanced SPAD values and spikelet fertility rates in IR64 and NPB rice varieties under both ambient and heat stress conditions. Moreover, there were notable increases in photosynthetic rate (7.4% to 52.6%) and leaf transpiration. N top dressing significantly (p < 0.05) increased the panicle length, panicle weight, number of secondary branches/panicle, filled grain/panicle, total spikelets/panicle, and yield/plant. However, there was no significant difference in the number of primary branches per panicle and 1000-grain weight. In addition, the number of unfilled grains/panicle decreased from 5.5 to 49.7% with N top dressing in both experiments. Applying N as a top dressing improved the spikelet fertility percentage and other yield components, resulting in a high yield/plant.

In the 20th century, global warming led to a 0.5 0C increase in air temperature; projections for the 21st century estimate a rise of 1.5–4.5 0C and higher temperatures are expected to become more common in the future. A rise in temperature above 33 °C has resulted in decreased rice production in various regions of the world. Heat stress affect the rice growth and development at different stages of crop growth. Heat Stress (HS) has a considerable negative effect on the potential for seed germination, leading to reduced seed viability and ineffective germination. During the tillering phase, high temperatures can lead to a reduction in both tiller number and biomass. Study reported that the optimum temperature for tillering is 25 °C during the day and 20°C at night. Tillers increased with increasing temperature in the range of 15 °C to 33 °C. Study found that temperatures above 33 °C damaged tillering. High temperatures can lead to reduced fertility in rice spikelets. This reduction is primarily due to impaired pollen sterility, issues with anther dehiscence, and failed stigma germination. High temperatures lead to spikelet infertility by decreasing pollen viability, restricting anther dehiscence, and preventing the germination of pollen tubes. In rice, the reproductive phase—which starts with panicle initiation and lasts until physiological grain maturity—is the most vulnerable stage to abiotic stresses. During anthesis, high temperatures significantly impede the dehiscence of anthers leads to spikelet sterility. High temperatures also adversely affect seed set and weight gaining, particularly shortly before or during anthesis. High temperatures interfere with the processes of pollen germination and tube growth by altering the balance of ions (such as Ca2þ), affecting carbohydrate metabolism. Elevated temperatures hinder spikelet differentiation, exacerbating spikelet degeneration and decreasing their overall number.

Against the backdrop of global climate warming, the frequency of high-temperature damage is on the rise, exerting a significant impact on rice growth and development, as well as yield and quality formation. Exposure to high-temperature damage during the rice flowering stage results in pollen sterility and reduced seed setting rate, consequently affecting yield and quality. The southern rice regions, as major grain-producing areas in China, frequently experience high-temperature damage during the heading and flowering stages of rice. Therefore, investigating the mechanisms underlying rice tolerance to high-temperature damage during the flowering stage holds great significance for ensuring global food security.Based on comprehensive existing studies, when rice is exposed to high temperatures during the flowering stage, it induces a series of physiological and reproductive disorders, including loss of pollen viability, abnormal spikelet opening, impaired anther dehiscence, reduced pollen germination rate, and inhibited pollen tube development. In response, rice copes with high-temperature stress through mechanisms such as activating physiological and biochemical regulation, initiating heat signal transduction, and regulating the expression of heat-tolerant genes. Furthermore, there are significant differences in the responses among rice varieties with varying heat tolerance.This study aims to elucidate in depth the heat tolerance mechanisms of rice during the flowering stage, thereby providing theoretical support for the identification of heat tolerance in rice varieties, the breeding of new stress-resistant varieties, and the optimization of supporting cultivation techniques.

No abstract available

Rice (Oryza sativa) is one of the world's most important cereal crops, contributing to food and financial security, particularly in developing countries. High temperature due to climate change seriously threatens sustainable rice production. Rice crops are adversely affected by heat stress at the morphological, physiological, and molecular levels, resulting in reduced yield and poor grain quality. Rice is highly sensitive to heat during the reproductive phase, causing pollen sterility, impaired pollen dehiscence, pollen germination, and tube growth, ultimately drastically reducing spikelet sterility and yield. High temperature also promotes the accumulation of reactive oxygen species in plant cells, resulting in multiple adverse effects, including damage to chloroplasts and cell membranes, inactivation of photosystems, reduced Rubisco activity, and impaired production of photoassimilates. In this review, we have synthesized the current knowledge on the effects of heat stress on rice and summarized QTLs, genes, and regulatory pathways underlying thermotolerance. We further evaluate conventional breeding, transgenics, and diverse omics-based strategies to breed high-yielding, heat-tolerant rice varieties. The precise molecular insights gained through various omics approaches are expected to advance our understanding of the intricate nature of heat stress tolerance in rice. Additionally, we highlight the emerging roles of microbiome, high-throughput phenotyping technologies, and artificial intelligence as promising tools for accelerating the development of heat-resilient rice.

Tartary buckwheat (Fagopyrum tataricum), a functional grain known for its medicinal and nutritional properties, has garnered significant attention due to its high flavonoid content and unique health benefits. Heat stress during the flowering stage can lead to sterility in Tartary buckwheat, resulting in reduced yields. This study investigates the effects of a treatment (30/27 °C for 7 days) on flower development, fertility, stress physiology, and gene expression in Tartary buckwheat, while also validating the efficacy of hormone treatments in alleviating the negative effects of heat stress. The results show that fertilization in Tartary buckwheat typically occurs within 3-5 days post-anthesis. By the 5th day, the stamen length in the heat-treated group was reduced by 13.89% compared to the control, while pistil length increased by 35.44%. Heat stress delayed the pistil stigma's transition into its highly receptive phase and caused a significant reduction in pollen viability by 15.25% after 5 days of treatment. Furthermore, after 7 days of treatment, the levels of H2O2 and O2- increased by 44.9% and 37.2%, respectively. However, Tartary buckwheat mitigated the impact of oxidative damage by enhancing the enzymatic activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). Transcriptome analysis revealed that heat stress significantly suppressed the expression of genes in hormone signaling pathways, such as indole-3-acetic acid (IAA), gibberellin (GA), and jasmonic acid (JA). Under heat treatment conditions, exogenous hormone application significantly regulated the dynamics of flower development. Specifically, after 3 days of heat treatment, all hormone treatments significantly inhibited the abnormal elongation of stamens, with GA notably suppressing the abnormal elongation of pistils. After 5 days, GA significantly promoted stamen elongation, while IAA and jasmonic acid (JA) significantly inhibited the abnormal elongation of pistils. After 7 days, all three hormone treatments significantly promoted stamen elongation and effectively inhibited abnormal pistil growth. These results suggest that under heat stress conditions, GA plays a key role in promoting stamen elongation, while IAA and JA inhibit the abnormal elongation of the pistil. Prolonged high temperatures can impair the function of floral organs, while JA treatment on the seventh day of heat treatment effectively restored pistil receptivity and significantly improved pollen vitality. In summary, this study provides in-depth insights into the mechanisms by which heat stress affects flower development in Tartary buckwheat, offering theoretical foundations and practical guidance for reducing the impact of heat stress on buckwheat yield.

No abstract available

Studies on the reproductive dynamics under heat stress are crucial to breed more tolerant cultivars. In tomato, cultivars, breeding lines, and wild species have been evaluated for their response to heat stress. Here, we addressed the study to a panel of selected landraces representing traditional genotypes that usually show high adaptation to local environments. In two experiments, spaced by 12 years, we set-up an identical experimental design with plants transplanted at two different dates to expose the second field to thermic stress with natural fluctuations. Such a strategy resulted in both a mild and severe stress in the two years. The landraces showed wide variation for both vegetative and reproductive traits; all traits were affected by heat, mostly with a significant Genotype*Environment interaction. A high broad-sense heritability was estimated for plant height, stigma position, pollen viability, and fruit weight. Low heritability estimates were found for the number of flowers, fruit set, and yield. Despite the interaction, traits recorded under control and heat conditions were positively correlated. Multivariate analysis located the genotypes in a topography that was stable under all conditions, except under the harshest temperatures. The study revealed that landraces present a wide variability for the response of reproductive traits to thermic challenges and that such a variation could be useful to dissect the traits with higher heritability and identify quantitative trait loci for breeding more resilient varieties.

Heat stress is one of the most important stresses that need to be addressed for better crop performance and to boost crop yield. A rise in temperature due to global warming affected plant growth and development and also reduces the quality and yield. Most of the field crops are sensitive to heat stress at the reproductive stage, which results in shortening the duration of seed filling and maturity, reducing the pollen fertility and stigma receptivity; thereby reducing the seed setting and seed yield. So, there is a need to mitigate the impact of heat stress in seed production for gaining better quality seeds. Even though plants have some morphological, physiological and biochemical adaptations to tolerate heat stress, additional practices are required for improving the quality and yield of seed crops. Breeding and biotechnological approaches can be used to identify the genes that are tolerant to high temperatures and to develop new varieties with heat stress tolerance. To mitigate the adverse effect of climate change and also to further boost the quality of hybrid seed availability in the country, alternative areas for hybrid seed production among major crops have been identified under AICRP-National Seed Project (crops), and this will help to maintain the adequate production and supply of quality seeds. Changing planting dates, nutrient management and irrigation management also can be practiced for improving crop growth under heat stress conditions. Seed inoculation with bacteria like plant growth-promoting rhizobacteria also improves the tolerance against heat stress by reducing the production of reactive oxygen species. Osmo-protectants have recently been recognized as crucial compounds that positively influence plants exposed to heat stress, as spraying osmoprotectants significantly enhances plant growth and antioxidant activity during heat stress situations. All these will undoubtedly assist in reducing the adverse impacts of heat stress, thereby enhancing plant productivity and food security amidst the present situations of climate change and global warming.

The Poaceae, or grasses, include many agriculturally important cereal crops such as rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare) and bread wheat (Triticum aestivum). Barley is a widely grown cereal crop used for stock feed, malting and brewing. Abiotic stresses, particularly global warming, are the major causes of crop yield losses by affecting fertility and seed set. However, effects of heat stress on reproductive structures and fertility in barley have not been extensively investigated. In this study we examined three commercial European spring barley varieties under high temperature conditions to investigate the effects on floret development. Using a combination of fertility assays, X-ray micro computed tomography, 3-dimensional modelling, cytology and immunolabelling, we observed that male reproductive organs are severely impacted by increased temperature, while the female reproductive organs are less susceptible. Importantly, the timing of stress relative to reproductive development had a significant impact on fertility in a cultivar-dependent manner, this was most significant at pollen mitosis stage with fertility ranged from 31.6-56.0% depending on cultivar. This work provides insight into how heat stress, when applied during male pollen mother cell meiosis and pollen mitosis, affects barley fertility and seed set, and also describes complementary invasive and non-invasive techniques to investigate floret development. This information will be used to identify and study barley cultivars that are less susceptible to heat stress at specific stages of floral development.

Rice yield is highly sensitive to increased temperature. Given the trend of increasing global temperatures, this sensitivity to higher temperatures poses a challenge for achieving global food security. Early seed development in rice is highly sensitive to unfavorable environmental conditions. Heat stress (HS) during this stage decreases seed size and fertility, thus reducing yield. Here, we explore the transgenerational phenotypic consequences of HS during early seed development on seed viability, germination, and establishment. To elucidate the impact of HS on the developmental events in post-zygotic rice seeds, we imposed moderate (35°C) and severe (39°C) HS treatments initiated 1 day after fertilization and maintained for 24, 48, or 72 h. The transient HS treatments altered the initiation of endosperm (ED) cellularization, seed size and/or the duration of spikelet ripening. Notably, seeds exposed to 24 and 48 h moderate HS exhibited higher germination rate compared to seeds derived from plants grown under control or severe HS. A short-term HS resulted in altered expression of Gibberellin (GA) and ABA biosynthesis genes during early seed development, and GA and ABA levels and starch content at maturity. The increased germination rate after 24 of moderate HS could be due to altered ABA sensitivity and/or increased starch level. Our findings on the impact of transient HS on hormone homeostasis provide an experimental framework to elucidate the underlying molecular and metabolic pathways.

Saline-alkali soils limit rice growth and production. With an increasing global population, enhancing rice salt tolerance is crucial for improving yields in these areas. This study investigated the developmental characteristics of young panicles and pollen fertility in two rice varieties, 58M and 58L, under salt stress. Results showed that 58M had more substantial salt tolerance during panicle development. RNA sequencing of 18 samples from both varieties under high salt stress (0 h, 6 h, and 24 h) identified 469 common differentially expressed genes (DEGs) and 2,308 DEGs between the varieties. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment highlighted significant pathways such as phenylpropanoid biosynthesis, protein processing, and flavonoid biosynthesis. Six gene co-expression modules related to salt tolerance were identified, with six candidate genes (LOC_Os05g38530, LOC_Os04g07920, LOC_Os12g02105, LOC_Os01g06580, LOC_Os06g49250, and LOC_Os06g48300) potentially linked to salt tolerance. These findings provide insights into rice salt tolerance mechanisms and offer new genetic resources for breeding salt-tolerant rice.