The effect of drought and heat stress on reproductive processes in cereals

Effect of high temperature on maize yield and grain components: A meta-analysis

Global warming poses a significant challenge to global food security, with maize playing a vital role as a staple crop in ensuring food availability worldwide. Therefore, investigating the impact of high temperature (HT) on maize cultivation is imperative for addressing food security concerns. Despite numerous studies exploring the effects of HT on maize growth and yield, a comprehensive understanding of these effects remains elusive due to variations in experimental environments, varieties, and growth stages. To solve these limitations, a meta-analysis was conducted to assess the effects of HT on maize yield and grain components, synthesizing data from 575 observations across 34 studies. The findings indicate that 1) HT significantly reduced grain yield by 32.7-40.9 % and grain starch content by 2.8-10.5 %; 2) the vicinity of kernel development stage (include silking, blister, milk) is the period when maize kernels are most sensitive to HT; 3) a significant negative correlation was observed between HT degree and their impact on grain yield (R2 = 0.38, P = 0.043); and 4) the effects of HT days and degrees on maize yield were equally important. In conclusion, this meta-analysis establishes a theoretical framework for enhancing the resilience of maize production and cultivation practices by comprehensively evaluating the impact of HT on yield and grain components.

Low molecular weight carbohydrates and abiotic stress tolerance in lentil (Lens culinaris Medikus): a review

Lentil (Lens culinaris Medikus) is a nutrient-rich, cool-season food legume that is high in protein, prebiotic carbohydrates, vitamins, and minerals. It is a staple food in many parts of the world, but crop performance is threatened by climate change, where increased temperatures and less predictable precipitation can reduce yield and nutritional quality. One mechanism that many plant species use to mitigate heat and drought stress is the production of disaccharides, oligosaccharides and sugar alcohols, collectively referred to as low molecular weight carbohydrates (LMWCs). Recent evidence indicates that lentil may also employ this mechanism - especially raffinose family oligosaccharides and sugar alcohols - and that these may be suitable targets for genomic-assisted breeding to improve crop tolerance to heat and drought stress. While the genes responsible for LMWC biosynthesis in lentil have not been fully elucidated, single nucleotide polymorphisms and putative genes underlying biosynthesis of LMWCs have been identified. Yet, more work is needed to confirm gene identity, function, and response to abiotic stress. This review i) summarizes the diverse evidence for how LMWCs are utilized to improve abiotic stress tolerance, ii) highlights current knowledge of genes that control LMWC biosynthesis in lentil, and iii) explores how LMWCs can be targeted using diverse genomic resources and markers to accelerate lentil breeding efforts for improved stress tolerance.

Observational evidence for groundwater influence on crop yields in the United States

As climate change shifts crop exposure to dry and wet extremes, a better understanding of factors governing crop response is needed. Recent studies identified shallow groundwater-groundwater within or near the crop rooting zone-as influential, yet existing evidence is largely based on theoretical crop model simulations, indirect or static groundwater data, or small-scale field studies. Here, we use observational satellite yield data and dynamic water table simulations from 1999 to 2018 to provide field-scale evidence for shallow groundwater effects on maize yields across the United States Corn Belt. We identify three lines of evidence supporting groundwater influence: 1) crop model simulations better match observed yields after improvements in groundwater representation; 2) machine learning analysis of observed yields and modeled groundwater levels reveals a subsidy zone between 1.1 and 2.5 m depths, with yield penalties at shallower depths and no effect at deeper depths; and 3) locations with groundwater typically in the subsidy zone display higher yield stability across time. We estimate an average 3.4% yield increase when groundwater levels are at optimum depth, and this effect roughly doubles in dry conditions. Groundwater yield subsidies occur ~35% of years on average across locations, with 75% of the region benefitting in at least 10% of years. Overall, we estimate that groundwater-yield interactions had a net monetary contribution of approximately $10 billion from 1999 to 2018. This study provides empirical evidence for region-wide groundwater yield impacts and further underlines the need for better quantification of groundwater levels and their dynamic responses to short- and long-term weather conditions.

Screening Wheat Genotypes for Specific Genes Linked to Drought Tolerance

Drought stress, which significantly affects growth and reduces grain yield, is one of the main problems for wheat crops. Producing promising drought-tolerant wheat cultivars with high yields is one of the main targets for wheat breeders. In this study, a total of seven drought-tolerant wheat genotypes were screened for the presence of 19 specific drought tolerance genes. The genotypes were tested under normal and drought conditions for two growing seasons. Four spike traits, namely, spike length (SPL), grain number per spike (GNPS), number of spikelets per spike (NSPS), and grain yield per spike (GYPS), were scored. The results revealed that drought stress decreased the SPL, GNPS, NSPS, and GYPS, with ranges ranging from 2.14 (NSPS) to 13.92% (GNPS) and from 2.40 (NSPS) to 11.09% (GYPS) in the first and second seasons, respectively. ANOVA revealed high genetic variation among the genotypes for each trait under each treatment. According to the drought tolerance indices, Omara 007 presented the highest level of drought tolerance (average of sum ranks = 3), whereas both Giza-36 genotypes presented the lowest level of drought tolerance (average of sum ranks = 4.8) among the genotypes tested. Among the 19 genes tested, 11 were polymorphic among the selected genotypes. Omara 007 and Omara 002 presented the greatest number of specific drought tolerance genes (nine) tested in this study, whereas Sohag-5, Giza-36, and PI469072 presented the lowest number of drought tolerance genes (four). The number of different genes between each pair of genotypes was calculated. Seven different genes were found between Omara 007 and Giza-36, Omara 007 and Sohag-5, and Omara 002 and PI469072. The results of this study may help to identify the best genotypes for crossing candidate genotypes, and not merely to genetically improve drought tolerance in wheat.

Cell death in bryophytes: emerging models to study core regulatory modules and conserved pathways

This review summarizes recent progress in our current understanding of the mechanisms underlying the cell death pathways in bryophytes, focusing on conserved pathways and particularities in comparison to angiosperms. Regulated cell death (RCD) plays key roles during essential processes along the plant life cycle. It is part of specific developmental programmes and maintains homeostasis of the organism in response to unfavourable environments. Bryophytes could provide valuable models to study developmental RCD processes as well as those triggered by biotic and abiotic stresses. Some pathways analogous to those present in angiosperms occur in the gametophytic haploid generation of bryophytes, allowing direct genetic studies. In this review, we focus on such RCD programmes, identifying core conserved mechanisms and raising new key questions to analyse RCD from an evolutionary perspective.

Discovery of anisiflupurin, an inhibitor of cytokinin dehydrogenase that mitigates heat-induced yield reduction in rice

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.

Potassium may mitigate drought stress by increasing stem carbohydrates and their mobilization into grains

Potassium (K) deficiency occurs commonly in crop plants. Optimal K nutrition is particularly important when plants are exposed to stress conditions (especially drought and heat) because a cellular demand for K increases. Low K in plant tissues is known to aggravate the effects of drought stress by impairing the osmoregulation process and the photosynthetic carbon metabolism. However, despite numerous publications about the role of K in enhancing tolerance to drought stress in crop plants, our understanding of the major mechanisms underlying the stress-mitigating effects of K is still limited. This paper summarizes and appraises the current knowledge on the major protective effects of K under drought stress, and then proposes a new K-related drought stress-mitigating mechanism, whereby optimal K nutrition may promote partitioning of carbohydrates in stem tissues and subsequent mobilization of these carbohydrates into developing grain under drought stress. The importance of stem reserves of carbohydrates is based on limited photosynthetic capacity during the grain-filling period under drought conditions due to premature leaf senescence as well as due to impaired assimilate transport from leaves to the developing grains. Plants with a high capacity to store large amounts of soluble carbohydrates in stems before anthesis and mobilize them into grain post-anthesis have a high potential to yield well in dry and hot environments. In practice, particular attention needs to be paid to the K nutritional status of plants grown with limited water supply, especially during grain filling. Because K is the mineral nutrient deposited mainly in stem, a special consideration should be given to stems of crop plants in research dealing with the effects of K on yield formation and stress mitigation.

Integrative phenotyping analyses reveal the relevance of the phyB-PIF4 pathway in Arabidopsis thaliana reproductive organs at high ambient temperature

BACKGROUND

The increasing ambient temperature significantly impacts plant growth, development, and reproduction. Uncovering the temperature-regulating mechanisms in plants is of high importance, for increasing our fundamental understanding of plant thermomorphogenesis, for its potential in applied science, and for aiding plant breeders in improving plant thermoresilience. Thermomorphogenesis, the developmental response to warm temperatures, has been primarily studied in seedlings and in the regulation of flowering time. PHYTOCHROME B and PHYTOCHROME-INTERACTING FACTORs (PIFs), particularly PIF4, are key components of this response. However, the thermoresponse of other adult vegetative tissues and reproductive structures has not been systematically evaluated, especially concerning the involvement of phyB and PIFs.

RESULTS

We screened the temperature responses of the wild type and several phyB-PIF4 pathway Arabidopsis mutant lines in combined and integrative phenotyping platforms for root growth in soil, shoot, inflorescence, and seed. Our findings demonstrate that phyB-PIF4 is generally involved in the relay of temperature signals throughout plant development, including the reproductive stage. Furthermore, we identified correlative responses to high ambient temperature between shoot and root tissues. This integrative and automated phenotyping was complemented by monitoring the changes in transcript levels in reproductive organs. Transcriptomic profiling of the pistils from plants grown under high ambient temperature identified key elements that may provide insight into the molecular mechanisms behind temperature-induced reduced fertilization rate. These include a downregulation of auxin metabolism, upregulation of genes involved auxin signalling, miRNA156 and miRNA160 pathways, and pollen tube attractants.

CONCLUSIONS

Our findings demonstrate that phyB-PIF4 involvement in the interpretation of temperature signals is pervasive throughout plant development, including processes directly linked to reproduction.

Heterogeneous and short-term effects of a changing climate on farmers' labor allocation: An empirical analysis of China

There is growing interest in the impact of climate change on agricultural labor supply in China, rigorous empirical evidence for this issue is insufficient. This potentially important channel through which climate change may affect agricultural labor supply has not received attention. Using a panel survey data of 100 administrative villages and 2977 farmers in China, we find that temperature and precipitation do affect farmers' labor allocation, 1°C increase from the current average temperature will reduce agricultural labor supply by 0.252%, and 1mm increase from the current average rainfall will reduce agricultural labor supply by 0.001%. Climate change also leads to the decline of net agricultural income, which creates distorted incentives for households to over-supply labor to non-agriculture. Moreover, farmers with relatively lower risk tolerance preferred to reduce the current supply of agricultural labor when net agricultural income is projected to decrease under climate change scenarios.

Overexpression of FERONIA receptor kinase MdMRLK2 regulates lignin accumulation and enhances water use efficiency in apple under long-term water deficit condition

Water use efficiency (WUE) is crucial for apple tree fitness and survival, especially in response to climatic changes. The receptor-like kinase FERONIA is reportedly an essential regulator of plant stress responses, but its role in regulating WUE under water deficit conditions is unclear. Here, we found that overexpressing the apple FERONIA receptor kinase gene, MdMRLK2, enhanced apple WUE under long-term water deficit conditions. Under drought treatment, 35S::MdMRLK2 apple plants exhibited higher photosynthetic capacity and antioxidant enzyme activities than wild-type (WT) plants. 35S::MdMRLK2 apple plants also showed increased biomass accumulation, root activity, and water potential compared to WT plants. Moreover, MdMRLK2 physically interacts with and phosphorylates cinnamoyl-CoA reductase 1, MdCCR1, an enzyme essential for lignin synthesis, at position Ser260. This interaction likely contributed to increased vessel density, vascular cylinder area, and lignin content in 35S::MdMRLK2 apple plants under drought conditions. Therefore, our findings reveal a novel function of MdMRLK2 in regulating apple WUE under water deficit conditions.

Supplemental Sodium Nitroprusside and Spermidine Regulate Water Balance and Chlorophyll Pigments to Improve Sunflower Yield under Terminal Drought

Drought is an inevitable environmental stress that drastically hampers the growth, productivity, and quality of food crops. Exogenous sodium nitroprusside and spermidine have decisive functions in the growth enhancement of plants; nevertheless, their specific role in mediating stress responses to improve drought tolerance in sunflowers at the reproductive stage (terminal drought) remains largely unknown. In the present study, we explored the positive effects of sodium nitroprusside and spermidine on physiological responses to increase in sunflower yield during periods of terminal drought. Initially, various doses (50, 100, 150, 200, 400 μM) for each sodium nitroprusside or spermidine were foliar sprayed to improve water content, chlorophylls, and biomass accumulation in sunflower seedlings under control (100% FC) and drought (60% FC) conditions. Optimized rates (100 μM for sodium nitroprusside) and (100 μM for spermidine) were further tested alone and in combination to assess drought tolerance potential and their ultimate impact on yield under drought stress. Drought exposure caused a marked reduction in relative water content (26%) and chlorophyll a (31%) and b (35%) contents; however, sodium nitroprusside and spermidine at 100 μM significantly improved the growth of sunflower (13%). Furthermore, combined use of sodium nitroprusside and spermidine at 100 + 100 μM markedly improved the achenes per head (16%), 1000-achene weight (14%), and ultimately grain (28%) and oil (21%) yields of sunflowers under drought stress. A strong association was found between the 1000-achene weight and the achene yield of sunflower. Hence, combined sodium nitroprusside and spermidine upregulate water balance and chlorophyll contents to increase sunflower yield under terminal drought.

Moderately reducing N input to mitigate heat stress in maize

In a warming climate, high temperature stress greatly threatens crop yields. Maize is critical to food security, but frequent extreme heat events coincide temporally and spatially with the period of kernel number determination (e.g., flowering stage), greatly limiting maize yields. In this context, how to increase or at least maintain maize yield has become more important. Nitrogen fertilizer (N) is widely used to improve maize yields, but its effect in heat stress is unclear. For this, we collected 1536 pairs of comparisons from 113 studies concerning N conducted in the past 20 years over China. We classified the data into two groups - without high temperature stress (NHT) and with high temperature stress during the critical period for maize kernel number determination (HT) - based on the national meteorological data. We comprehensively evaluated N effects on grain yield under HT and NHT using meta-analysis. The effect of N on maize yield became significantly smaller in HT than that in NHT. In NHT, soil characteristics, crop management practices, and climatic conditions all significantly affected N effects on maize yield, but in HT, only a few factors such as soil organic matter and mean annual precipitation significantly affected N effects. Hence, it is difficult to improve N effect by improving soil characteristics and crop management when meeting with high temperature stress during flowering. On average, N effect increased with increased N input, but there were respective N input thresholds in NHT and HT, beyond which N effects on maize yield remained stable. According to the thresholds, it is speculated that moderately reducing N input (~20 %) likely increased high temperature tolerance of maize during flowering. These findings have important implications for the optimization of N management under a warming climate.

Heliotropium thermophilum adapts to high soil temperature in natural conditions due to its highly active antioxidant system protecting its photosynthetic machinery

Heliotropium thermophilum (Boraginaceae) plants have strong antioxidant properties. This study investigated the effectiveness of the antioxidant system in protecting the photosynthetic machinery of H. thermophilum . Plants were obtained from Kızıldere geothermal area in Buharkent district, Aydın, Turkey. Plants in the geothermal area that grew at 25-35°C were regarded as the low temperature group, while those that grew at 55-65°C were regarded as the high temperature group. We analysed the physiological changes of these plants at the two temperature conditions at stage pre-flowering and flowering. We meaured the effect of high soil temperature on water potential, malondialdehyde, cell membrane stability, and hydrogen peroxide analysis to determine stress levels on leaves and roots. Changes in antioxidant enzyme activities, ascorbate and chlorophyll content, chlorophyll fluorescence, photosynthetic gas exchange parameters, and photosynthetic enzymes (Rubisco and invertase) activities were also determined. Our results showed minimal changes to stress levels, indicating that plants were tolerant to high soil temperatures. In general, an increase in antioxidant enzyme activities, ascorbat levels, and all chlorophyll fluorescence parameters except for non-photochemical quenching (NPQ) and F v /F m were observed. The pre-flowering and flowering stages were both characterised by decreased NPQ, despite F v /F m not changing. Additionally, there was a rise in the levels of photosynthetic gas exchange parameters, Rubisco, and invertase activities. High temperature did not affect photosynthetic yield because H. thermophilum was found to stimulate antioxidant capacity, which reduces oxidative damage and maintains its photosynthetic machinery in high temperature conditions and therefore, it is tolerant to high soil temperature.

Improving resilience to high temperature in drought: water replenishment enhances sucrose and amino acid metabolisms in maize grain

Heat stress poses a significant threat to maize, especially when combined with drought. Recent research highlights the potential of water replenishment to ameliorate grain weight loss. However, the mitigating mechanisms of heat in drought stress, especially during the crucial early grain-filling stage, remain poorly understood. We investigated the mechanism for mitigating heat in drought stress by water replenishment from the 12th to the 32nd days after silking in a controlled greenhouse experiment (Exp. I) and field trial (Exp. II). A significant reduction in grain weight was observed in heat stress compared to normal conditions. When water replenishment was applied to increase soil water content (SWC) under heat stress, the grain yield exhibited a notable increase ranging from 28.4 to 76.9%. XY335 variety was used for transcriptome sequencing to analyze starch biosynthesis and amino acid metabolisms in Exp. I. With water replenishment, the transcripts of genes responsible for trehalose 6-phosphate phosphates (TPP), alpha-trehalase (TRE), ADP-glcpyrophosphorylase, and starch synthase activity were stimulated. Additionally, the expression of genes encoding TPP and TRE contributed to an enhanced conversion of trehalose to glucose. This led to the conversion of sucrose from glucose-1-phosphate to ADP-glucose and ADP-glucose to amylopectin, ultimately increasing starch production by 45.1%. Water replenishment to boost SWC during heat stress also elevated the levels of essential amino acids in maize, including arginine, serine, tyrosine, leucine, glutamic acid, and methionine, providing valuable support to maize plants in adversity. Field trials further validated the positive impact of water replenishment on SWC, resulting in a notable increase in grain yield ranging from 7.1 to 9.2%. This study highlights the vital importance of adapting to abiotic stress and underscores the necessity of developing strategies to counteract its adverse effects on crop yield.

Deleterious Effects of Heat Stress on the Tomato, Its Innate Responses, and Potential Preventive Strategies in the Realm of Emerging Technologies

The tomato is a fruit vegetable rich in nutritional and medicinal value grown in greenhouses and fields worldwide. It is severely sensitive to heat stress, which frequently occurs with rising global warming. Predictions indicate a 0.2 °C increase in average surface temperatures per decade for the next three decades, which underlines the threat of austere heat stress in the future. Previous studies have reported that heat stress adversely affects tomato growth, limits nutrient availability, hammers photosynthesis, disrupts reproduction, denatures proteins, upsets signaling pathways, and damages cell membranes. The overproduction of reactive oxygen species in response to heat stress is toxic to tomato plants. The negative consequences of heat stress on the tomato have been the focus of much investigation, resulting in the emergence of several therapeutic interventions. However, a considerable distance remains to be covered to develop tomato varieties that are tolerant to current heat stress and durable in the perspective of increasing global warming. This current review provides a critical analysis of the heat stress consequences on the tomato in the context of global warming, its innate response to heat stress, and the elucidation of domains characterized by a scarcity of knowledge, along with potential avenues for enhancing sustainable tolerance against heat stress through the involvement of diverse advanced technologies. The particular mechanism underlying thermotolerance remains indeterminate and requires further elucidatory investigation. The precise roles and interplay of signaling pathways in response to heat stress remain unresolved. The etiology of tomato plants' physiological and molecular responses against heat stress remains unexplained. Utilizing modern functional genomics techniques, including transcriptomics, proteomics, and metabolomics, can assist in identifying potential candidate proteins, metabolites, genes, gene networks, and signaling pathways contributing to tomato stress tolerance. Improving tomato tolerance against heat stress urges a comprehensive and combined strategy including modern techniques, the latest apparatuses, speedy breeding, physiology, and molecular markers to regulate their physiological, molecular, and biochemical reactions.

GDSL Lipase Gene HTA1 Negatively Regulates Heat Tolerance in Rice Seedlings by Regulating Reactive Oxygen Species Accumulation

High temperature is a significant environmental stress that limits plant growth and agricultural productivity. GDSL lipase is a hydrolytic enzyme with a conserved GDSL sequence at the N-terminus, which has various biological functions, such as participating in plant growth, development, lipid metabolism, and stress resistance. However, little is known about the function of the GDSL lipase gene in the heat tolerance of rice. Here, we characterized a lipase family protein coding gene HTA1, which was significantly induced by high temperature in rice. Rice seedlings in which the mutant hta1 was knocked out showed enhanced heat tolerance, whereas the overexpressing HTA1 showed more sensitivity to heat stress. Under heat stress, hta1 could reduce plant membrane damage and reactive oxygen species (ROS) levels and elevate the activity of antioxidant enzymes. Moreover, real-time quantitative PCR (RT-qPCR) analysis showed that mutant hta1 significantly activated gene expression in antioxidant enzymes, heat response, and defense. In conclusion, our results suggest that HTA1 negatively regulates heat stress tolerance by modulating the ROS accumulation and the expression of heat-responsive and defense-related genes in rice seedlings. This research will provide a valuable resource for utilizing HTA1 to improve crop heat tolerance.

PbHsfC1a-coordinates ABA biosynthesis and H2O2 signalling pathways to improve drought tolerance in Pyrus betulaefolia

Abiotic stresses have had a substantial impact on fruit crop output and quality. Plants have evolved an efficient immune system to combat abiotic stress, which employs reactive oxygen species (ROS) to activate the downstream defence response signals. Although an aquaporin protein encoded by PbPIP1;4 is identified from transcriptome analysis of Pyrus betulaefolia plants under drought treatments, little attention has been paid to the role of PIP and ROS in responding to abiotic stresses in pear plants. In this study, we discovered that overexpression of PbPIP1;4 in pear callus improved tolerance to oxidative and osmotic stresses by reconstructing redox homeostasis and ABA signal pathways. PbPIP1;4 overexpression enhanced the transport of H2O2 into pear and yeast cells. Overexpression of PbPIP1;4 in Arabidopsis plants mitigates the stress effects caused by adding ABA, including stomatal closure and reduction of seed germination and seedling growth. Overexpression of PbPIP1;4 in Arabidopsis plants decreases drought-induced leaf withering. The PbPIP1;4 promoter could be bound and activated by TF PbHsfC1a. Overexpression of PbHsfC1a in Arabidopsis plants rescued the leaf from wilting under drought stress. PbHsfC1a could bind to and activate AtNCED4 and PbNCED4 promoters, but the activation could be inhibited by adding ABA. Besides, PbNCED expression was up-regulated under H2O2 treatment but down-regulated under ABA treatment. In conclusion, this study revealed that PbHsfC1a is a positive regulator of abiotic stress, by targeting PbPIP1;4 and PbNCED4 promoters and activating their expression to mediate redox homeostasis and ABA biosynthesis. It provides valuable information for breeding drought-resistant pear cultivars through gene modification.

The role of priming and memory in rice environmental stress adaptation: Current knowledge and perspectives

Plant responses to abiotic stresses are dynamic, following the unpredictable changes of physical environmental parameters such as temperature, water and nutrients. Physiological and phenotypical responses to stress are intercalated by periods of recovery. An earlier stress can be remembered as 'stress memory' to mount a response within a generation or transgenerationally. The 'stress priming' phenomenon allows plants to respond quickly and more robustly to stressors to increase survival, and therefore has significant implications for agriculture. Although evidence for stress memory in various plant species is accumulating, understanding of the mechanisms implicated, especially for crops of agricultural interest, is in its infancy. Rice is a major food crop which is susceptible to abiotic stresses causing constraints on its cultivation and yield globally. Advancing the understanding of the stress response network will thus have a significant impact on rice sustainable production and global food security in the face of climate change. Therefore, this review highlights the effects of priming on rice abiotic stress tolerance and focuses on specific aspects of stress memory, its perpetuation and its regulation at epigenetic, transcriptional, metabolic as well as physiological levels. The open questions and future directions in this exciting research field are also laid out.

Plant responses to co-occurring heat and water deficit stress: A comparative study of tolerance mechanisms in old and modern wheat genotypes

Global climate change increases the likelihood of co-occurrence of hot and dry spells with increased intensity, frequency, and duration. Studying the impact of the two stresses provide a better understanding of tolerance mechanisms in wheat, and our study was focused on revealing plant stress responses to different severities of combined stress at two phenophases in old and modern wheat genotypes. During the stem elongation and anthesis stages, plants were exposed to four treatments: control, deficit irrigation, combined heat, and deficit irrigation at 31 °C (HD31) and 37 °C (HD37). The modern genotypes were less affected by deficit irrigation at stem elongation as they maintained higher photosynthesis, stomatal conductance, and leaf cooling than old genotypes. When the HD37 stress was imposed during anthesis, the modern genotypes exhibited superior performance compared to the old, which was due to their higher photosynthetic rates resulting from improved biochemical regulation and a higher chlorophyll content. The plant responses varied during two phenophases under the combined stress exposure. Genotypes subjected to HD37 stress during stem elongation, photosynthesis was mainly controlled by stomatal regulation, whereas at anthesis it was predominated by biochemical regulation. These findings contribute to a deeper comprehension of plant tolerance mechanisms in response to different intensities of co-occurring hot and dry weather conditions.

Endophyte Inoculation and Elevated Potassium Supply on Productivity, Growth and Physiological Parameters of Spring Barley (Hordeum vulgare L.) Genotypes over Contrasting Seasons

In recent years, recurrent droughts have significantly affected spring barley production, reducing the quantity and quality of grain. This study aims to identify genotype-specific traits and the drought resilience of six different Hordeum vulgare L. (spring barley) genotypes, while also examining the potential of potassium application and fungal endophyte Serendipita indica inoculation to mitigate the negative effects of dry periods during the growing season. Field experiments were conducted over a three-year period from 2020 to 2022, measuring physiological, growth, and yield parameters. To get insight into the physiological state of the plants, we measured the soluble sugars content and the ratio of stable carbon isotopes in the flag leaf tissue, which reflects conditions during its formation. The dominant factors that influenced the measured parameters were the genotypes and seasons, as well as their interaction, rather than other experimental factors. The results showed that the Spitfire and Accordine varieties were the best performing in both the 2020 and 2021 seasons, as indicated by their yield. However, in the drier 2022 season, the yield of these two varieties decreased significantly (to 55% for Spitfire and to 69% for Accordine of their yield in 2021), while for the arid-region genotypes, it remained at the same level as the previous year. This study sheds light on the potential of various genotypes to withstand periods of drought and the effectiveness of using potassium application and S. indica inoculation as mitigation approaches.

The roles of non-coding RNAs in male reproductive development and abiotic stress responses during this unique process in flowering plants

Successful male reproductive development is the guarantee for sexual reproduction of flowering plants. Male reproductive development is a complicated and multi-stage process that integrates physiological processes and adaptation and tolerance to a myriad of environmental stresses. This well-coordinated process is governed by genetic and epigenetic machineries. Non-coding RNAs (ncRNAs) play pleiotropic roles in the plant growth and development. The identification, characterization and functional analysis of ncRNAs and their target genes have opened a new avenue for comprehensively revealing the regulatory network of male reproductive development and its response to environmental stresses in plants. This review briefly addresses the types, origin, biogenesis and mechanisms of ncRNAs in plants, highlights important updates on the roles of ncRNAs in regulating male reproductive development and emphasizes the contribution of ncRNAs, especially miRNAs and lncRNAs, in responses to abiotic stresses during this unique process in flowering plants.

The novel chaperonin 10 like protein (SbCPN10L) from Salicornia brachiata (Roxb.) augment the heat stress tolerance in transgenic tobacco

The heat stress is a significant environmental challenge and impede the plant growth, development and productivity. The characterization and utilization of novel genes for improving stress tolerance represents a paramount approach in crop breeding. In the present study, we report on cloning of a novel heat-induced chaperonin 10-like gene (SbCPN10L) from Salicornia brachiata and elucidation of its in-planta role in conferring the heat stress endurance. The transgenic tobacco over-expressing SbCPN10L gene exhibited enhanced growth attributes such as higher rate of seed germination, germination and vigor index at elevated (35 ± 1 °C) temperature (eT). The SbCPN10L tobacco exhibited greenish and healthy seedling growth under stress. Compared with control tobacco at eT, the transgenic tobacco had higher water contents, membrane stability index, stress tolerance index and photosynthetic pigments. Lower electrolyte leakage and less accumulation of malondialdehyde, hydrogen peroxide and reactive oxygen species indicated better heat stress tolerance in transgenic tobacco over-expressing SbCPN10L gene. Transgenic tobacco accumulated higher contents of sugars, starch, amino acids and polyphenols at eT. The negative solute potential observed in transgenic tobacco contributed to maintain water content and support improved growth under stress. The up-regulation of NtAPX, NtPOX and NtSOD in transgenic tobacco under stress indicated higher ROS scavenging ability and better physiological conditioning. The results recommend the SbCPN10L gene as a potential candidate gene with an ability to confer heat stress tolerance for climate resilient crops.

Moderate high temperature is beneficial or detrimental depending on carbon availability in the green alga Chlamydomonas reinhardtii

High temperatures impair plant growth and reduce agricultural yields, but the underlying mechanisms remain elusive. The unicellular green alga Chlamydomonas reinhardtii is an excellent model to study heat responses in photosynthetic cells due to its fast growth rate, many similarities in cellular processes to land plants, simple and sequenced genome, and ample genetic and genomics resources. Chlamydomonas grows in light by photosynthesis and with externally supplied acetate as an organic carbon source. Understanding how organic carbon sources affect heat responses is important for the algal industry but remains understudied. We cultivated wild-type Chlamydomonas under highly controlled conditions in photobioreactors at 25 °C (control), 35 °C (moderate high temperature), or 40 °C (acute high temperature) with or without constant acetate supply for 1 or 4 day. Treatment at 35 °C increased algal growth with constant acetate supply but reduced algal growth without sufficient acetate. The overlooked and dynamic effects of 35 °C could be explained by induced acetate uptake and metabolism. Heat treatment at 40 °C for more than 2 day was lethal to algal cultures with or without constant acetate supply. Our findings provide insights to understand algal heat responses and help improve thermotolerance in photosynthetic cells.

Antioxidative response of parthenocarpic tomato, iaa9-3 and iaa9-5, under heat stress condition

It has previously been shown that parthenocarpic tomato mutants, iaa9-3 and iaa9-5, can adapt, grow, and produce fruit under heat-stress conditions. However, the physiological processes in those two mutants especially for the enzymatic system that works to neutralize ROS are not clear. The objective of this research was to determine how the scavenging enzyme system responds to the heat stress in those mutants. The iaa9-3, iaa9-5, and WT-MT as a control were cultivated under two environmental conditions; normal and heat stress conditions. Vegetative and reproductive growth were observed during cultivation period. The activities of catalase (CAT), ascorbate peroxidase (APX) and superoxide dismutase (SOD) were investigated in both wild-type and parthenocarpic tomato mutants under normal and heat stress conditions. The results showed that under heat stress condition, the mutants, iaa9-3 and iaa9-5, and WT-MT resulted in reduction of the vegetative growth, but those mutants showed better growth than WT-MT. Higher chlorophyll content in iaa9-3 and iaa9-5 was observed under normal or heat stress condition. Despite their growth reduction under heat stress conditions, iaa9-3 and iaa9-5 resulted in the significant higher CAT, APX and SOD activity than WT-MT. The results suggest that higher chlorophyll content and enhanced CAT, APX and SOD activity in the iaa9-3 and iaa9-5 mutants are adaptive strategies to survive in heat stress conditions.

Role of Microbes in Alleviating Crop Drought Stress: A Review

Drought stress is an annual global phenomenon that has devastating effects on crop production, so numerous studies have been conducted to improve crop drought resistance. Plant-associated microbiota play a crucial role in crop health and growth; however, we have a limited understanding of the key processes involved in microbiome-induced crop adaptation to drought stress. In this review, we summarize the adverse effects of drought stress on crop growth in terms of germination, photosynthesis, nutrient uptake, biomass, and yield, with a focus on the response of soil microbial communities to drought stress and plant-microbe interactions under drought stress. Moreover, we review the morpho-physiological, biochemical, and molecular mechanisms underlying the mitigation effect of microbes on crop drought stress. Finally, we highlight future research directions, including the characterization of specific rhizosphere microbiome species with corresponding root exudates and the efficiency of rhizobacteria inoculants under drought conditions. Such research will advance our understanding of the complex interactions between crops and microbes and improve crop resistance to drought stress through the application of beneficial drought-adaptive microbes.

Climate risk zoning for wheat crops in the southeastern region of Brazil

BACKGROUND

Wheat (Triticum aestivum L.) is the second most consumed food in the world. One way to meet this demand is the expansion of wheat cultivation to the Brazilian Cerrado in the southeastern region. However, one of the major limitations is that there are few studies related to wheat climate risk zoning. Thus, this study aimed to determine the agroclimatic zoning of wheat by estimating the water needs satisfaction index (ISNA) in the southeastern region of Brazil. For this purpose, a 60-year historical series of meteorological data was used to calculate the potential evapotranspiration, crop evapotranspiration, and climatological water balance values. To define the agroclimatic zones of wheat and sowing date, the ISNA method was used. The data were analyzed using descriptive statistics to determine the variations. To obtain the agroclimatic zoning of wheat, the geostatistical method of kriging interpolation was used.

RESULTS

The regions with the highest rainfall are the south of Minas Gerais and the coast of São Paulo. The sowing period directly impacts the development of the crop, the available water capacity and the ISNA values indicated the spring and summer had better cultivation conditions, and the best window for wheat cultivation is concentrated in the fall due to the limitation of biotic factors.

CONCLUSION

In terms of altitude (>700 m), Minas Gerais has 39.4% of the area suitable for wheat cultivation. Thus, climatic variations within and between the states of the southeastern region should be considered for the positioning of wheat cultivars in these regions to obtain the maximum yield. © 2023 Society of Chemical Industry.

Multivariate Analysis Compares and Evaluates Heat Tolerance of Potato Germplasm

High temperature is the most important environmental factor limiting potato (Solanum tuberosum L.) yield. The tuber yield has been used to evaluate the heat tolerance of some potato cultivars, but potato yield was closely correlated with the maturation period. Therefore, it is necessary to employ different parameters to comprehensively analyze and evaluate potato tolerance to heat stress. This study aimed to investigate physiologic changes during growth and development, and develop accurate heat tolerance evaluation methods of potato cultivars under heat stress. About 93 cultivars (including foreign elite lines, local landraces and cultivars) were screened using an in vitro tuber-inducing system (continuous darkness and 8% sucrose in the culture medium) under heat stress (30 °C) and normal (22 °C) conditions for 30 days. The tuber yield and number decreased significantly under heat stress compared to the control. A total of 42 cultivars were initially selected depending on tuber formation, after in vitro screening, further testing of selected cultivars was conducted in ex vitro conditions. The screened cultivars were further exposed to heat stress (35 °C/28 °C, day/night) for 60 days. Heat stress led to an increase in the plant height growth rate, fourth internode growth rate, and membrane damage, and due to heat-induced damage to chloroplasts, decrease in chlorophyll biosynthesis and photosynthetic efficiency. Three principal components were extracted by principal component analysis. Correlation and regression analysis showed that heat tolerance is positively correlated with the plant height growth rate, fourth internode growth rate, the content of chlorophyll b, photosynthetic rate, stomatal conductance, transpiration rate, tuber number, and tuber yield, and negatively correlated with the cell membrane injury level. The nine traits are accurate and representative indicators for evaluating potato tolerance to heat stress and could determine a relatively high mean forecast accuracy of 100.0% for the comprehensive evaluation value. Through cluster analysis and screening, cultivar FA, D73, and C132 had the highest heat comprehensive evaluation value, which could be further selected as heat-resistant varieties. This study provides insights into the different physiological mechanisms and accurate evaluation methods of potato cultivars under heat stress, which could be valuable for further research and breeding.

Effect of drought stress on wheat (Triticum durum) growth and metabolism: insight from GABA shunt, reactive oxygen species and dehydrin genes expression

Activation of γ-aminobutyric acid (GABA) shunt pathway and upregulation of dehydrins are involved in metabolic homeostasis and protective mechanisms against drought stress. Seed germination percentage, seedling growth, levels of GABA, alanine, glutamate, malondialdehyde (MDA), and the expression of glutamate decarboxylase (GAD ) and dehydrin (dhn and wcor ) genes were examined in post-germination and seedlings of four durum wheat (Triticum durum L.) cultivars in response to water holding capacity levels (80%, 50%, and 20%). Data showed a significant decrease in seed germination percentage, seedling length, fresh and dry weight, and water content as water holding capacity level was decreased. Levels of GABA, alanine, glutamate, and MDA were significantly increased with a negative correlation in post-germination and seedling stages as water holding capacity level was decreased. Prolonged exposure to drought stress increased the GAD expression that activated GABA shunt pathway especially at seedlings growth stage to maintain carbon/nitrogen balance, amino acids and carbohydrates metabolism, and plant growth regulation under drought stress. The mRNA transcripts of dhn and wcor significantly increased as water availability decreased in all wheat cultivars during the post-germination stage presumably to enhance plant tolerance to drought stress by cell membrane protection, cryoprotection of enzymes, and prevention of reactive oxygen species (ROS) accumulation. This study showed that the four durum wheat cultivars responded differently to drought stress especially during the seedling growth stage which might be connected with ROS scavenging systems and the activation of antioxidant enzymes that were associated with activation of GABA shunt pathway and the production of GABA in durum seedlings.

Identification of transcriptional modules linked to the drought response of Brassica napus during seed development and their mitigation by early biotic stress

In order to capture the drought impacts on seed quality acquisition in Brassica napus and its potential interaction with early biotic stress, seeds of the 'Express' genotype of oilseed rape were characterized from late embryogenesis to full maturity from plants submitted to reduced watering (WS) with or without pre-occurring inoculation by the telluric pathogen Plasmodiophora brassicae (Pb + WS or Pb, respectively), and compared to control conditions (C). Drought as a single constraint led to significantly lower accumulation of lipids, higher protein content and reduced longevity of the WS-treated seeds. In contrast, when water shortage was preceded by clubroot infection, these phenotypic differences were completely abolished despite the upregulation of the drought sensor RD20. A weighted gene co-expression network of seed development in oilseed rape was generated using 72 transcriptomes from developing seeds from the four treatments and identified 33 modules. Module 29 was highly enriched in heat shock proteins and chaperones that showed a stronger upregulation in Pb + WS compared to the WS condition, pointing to a possible priming effect by the early P. brassicae infection on seed quality acquisition. Module 13 was enriched with genes encoding 12S and 2S seed storage proteins, with the latter being strongly upregulated under WS conditions. Cis-element promotor enrichment identified PEI1/TZF6, FUS3 and bZIP68 as putative regulators significantly upregulated upon WS compared to Pb + WS. Our results provide a temporal co-expression atlas of seed development in oilseed rape and will serve as a resource to characterize the plant response towards combinations of biotic and abiotic stresses.

A quick and effective method for thermostability differentiation in cucumber (Cucumis sativus L.)

High temperature affects the growth and production of cucumber. Selecting thermotolerant cucumber cultivars is conducive to coping with high temperatures and improving production. Thus, a quick and effective method for screening thermotolerant cucumber cultivars is needed. In this study, four cucumber cultivars were used to identify heat resistance indexes. The morphological, physiological and biochemical indexes were measured. When exposed to high temperatures, thermotolerant cucumber had a more stable photosystem, membrane, and oxidation-reduction systems. The impact of high temperatures on plants is multifaceted, and the accurate discrimination of heat resistance cannot be achieved solely based on a single or multiple indicators. Therefore, principal component analysis (PCA) was employed to comprehensively evaluate the heat resistance of cucumber plants. The results showed that the heat resistance obtained by PCA was significantly correlated with the heat injury index. In addition, the stepwise regression equation identified two heat-related indices, hydrogen peroxide content (H2 O2 ) and photosynthetic operating efficiency (Fq'/Fm'), and they can quickly distinguish the heat resistance of the other 8 cucumber cultivars. These results will help to accelerate the selection of thermotolerant resources and assist in cucumber breeding.

Nanoenabled Enhancement of Plant Tolerance to Heat and Drought Stress on Molecular Response

Global warming has posed significant pressure on agricultural productivity. The resulting abiotic stresses from high temperatures and drought have become serious threats to plants and subsequent global food security. Applying nanomaterials in agriculture can balance the plant's oxidant level and can also regulate phytohormone levels and thus maintain normal plant growth under heat and drought stresses. Nanomaterials can activate and regulate specific stress-related genes, which in turn increase the activity of heat shock protein and aquaporin to enable plants' resistance against abiotic stresses. This review aims to provide a current understanding of nanotechnology-enhanced plant tolerance to heat and drought stress. Molecular mechanisms are explored to see how nanomaterials can alleviate abiotic stresses on plants. In comparison with organic molecules, nanomaterials offer the advantages of targeted transportation and slow release. These advantages help the nanomaterials in mitigating drought and heat stress in plants.

The impact of heat stress in plant reproduction

The increment in global temperature reduces crop productivity, which in turn threatens food security. Currently, most of our food supply is produced by plants and the human population is estimated to reach 9 billion by 2050. Gaining insights into how plants navigate heat stress in their reproductive phase is essential for effectively overseeing the future of agricultural productivity. The reproductive success of numerous plant species can be jeopardized by just one exceptionally hot day. While the effects of heat stress on seedlings germination and root development have been extensively investigated, studies on reproduction are limited. The intricate processes of gamete development and fertilization unfold within a brief timeframe, largely concealed within the flower. Nonetheless, heat stress is known to have important effects on reproduction. Considering that heat stress typically affects both male and female reproductive structures concurrently, it remains crucial to identify cultivars with thermotolerance. In such cultivars, ovules and pollen can successfully undergo development despite the challenges posed by heat stress, enabling the completion of the fertilization process and resulting in a robust seed yield. Hereby, we review the current understanding of the molecular mechanisms underlying plant resistance to abiotic heat stress, focusing on the reproductive process in the model systems of Arabidopsis and Oryza sativa.

Effects of Elevated Temperature on Pisum sativum Nodule Development: II-Phytohormonal Responses

High temperature is one of the most important factors limiting legume productivity. We have previously shown the induction of senescence in the apical part of nodules of the pea SGE line, formed by Rhizobium leguminosarum bv. viciae strain 3841, when they were exposed to elevated temperature (28 °C). In this study, we analyzed the potential involvement of abscisic acid (ABA), ethylene, and gibberellins in apical senescence in pea nodules under elevated temperature. Immunolocalization revealed an increase in ABA and 1-aminocyclopropane-1-carboxylic acid (ACC, the precursor of ethylene biosynthesis) levels in cells of the nitrogen fixation zone in heat-stressed nodules in 1 day of exposure compared to heat-unstressed nodules. Both ABA and ethylene appear to be involved in the earliest responses of nodules to heat stress. A decrease in the gibberellic acid (GA3) level in heat-stressed nodules was observed. Exogenous GA3 treatment induced a delay in the degradation of the nitrogen fixation zone in heat-stressed nodules. At the same time, a decrease in the expression level of many genes associated with nodule senescence, heat shock, and defense responses in pea nodules treated with GA3 at an elevated temperature was detected. Therefore, apical senescence in heat-stressed nodules is regulated by phytohormones in a manner similar to natural senescence. Gibberellins can be considered as negative regulators, while ABA and ethylene can be considered positive regulators.

Barley shows reduced Fusarium head blight under drought and modular expression of differentially expressed genes under combined stress

Plants often face simultaneous abiotic and biotic stress conditions; however, physiological and transcriptional responses under such combined stress conditions are still not fully understood. Spring barley (Hordeum vulgare) is susceptible to Fusarium head blight (FHB), which is strongly affected by weather conditions. We therefore studied the potential influence of drought on FHB severity and plant responses in three varieties of different susceptibility. We found strongly reduced FHB severity in susceptible varieties under drought. The number of differentially expressed genes (DEGs) and strength of transcriptomic regulation reflected the concentrations of physiological stress markers such as abscisic acid or fungal DNA contents. Infection-related gene expression was associated with susceptibility rather than resistance. Weighted gene co-expression network analysis revealed 18 modules of co-expressed genes that reflected the pathogen- or drought-response in the three varieties. A generally infection-related module contained co-expressed genes for defence, programmed cell death, and mycotoxin detoxification, indicating that the diverse genotypes used a similar defence strategy towards FHB, albeit with different degrees of success. Further, DEGs showed co-expression in drought- or genotype-associated modules that correlated with measured phytohormones or the osmolyte proline. The combination of drought stress with infection led to the highest numbers of DEGs and resulted in a modular composition of the single-stress responses rather than a specific transcriptional output.

Morpho-Anatomical, Physiological and Biochemical Adjustments in Response to Heat and Drought Co-Stress in Winter Barley

This study aimed to investigate the combined effect of high temperatures 10 °C above the optimum and water withholding during microgametogenesis on vegetative processes and determine the response of winter barley genotypes with contrasting tolerance. For this purpose, two barley varieties were analyzed to compare the effect of heat and drought co-stress on their phenology, morpho-anatomy, physiological and biochemical responses and yield constituents. Genotypic variation was observed in response to heat and drought co-stress, which was attributed to differences in anatomy, ultrastructure and physiological and metabolic processes. The co-stress-induced reduction in relative water content, total soluble protein and carbohydrate contents, photosynthetic pigment contents and photosynthetic efficiency of the sensitive Spinner variety was significantly greater than the tolerant Lambada genotype. Based on these observations, it has been concluded that the heat-and-drought stress-tolerance of the Lambada variety is related to the lower initial chlorophyll content of the leaves, the relative resistance of photosynthetic pigments towards stress-triggered degradation, retained photosynthetic parameters and better-preserved leaf ultrastructure. Understanding the key factors underlying heat and drought co-stress tolerance in barley may enable breeders to create barley varieties with improved yield stability under a changing climate.

Similar photosynthetic but different yield responses of C3 and C4 crops to elevated O3

The deleterious effects of ozone (O3) pollution on crop physiology, yield, and productivity are widely acknowledged. It has also been assumed that C4 crops with a carbon concentrating mechanism and greater water use efficiency are less sensitive to O3 pollution than C3 crops. This assumption has not been widely tested. Therefore, we compiled 46 journal articles and unpublished datasets that reported leaf photosynthetic and biochemical traits, plant biomass, and yield in five C3 crops (chickpea, rice, snap bean, soybean, and wheat) and four C4 crops (sorghum, maize, Miscanthus × giganteus, and switchgrass) grown under ambient and elevated O3 concentration ([O3]) in the field at free-air O3 concentration enrichment (O3-FACE) facilities over the past 20 y. When normalized by O3 exposure, C3 and C4 crops showed a similar response of leaf photosynthesis, but the reduction in chlorophyll content, fluorescence, and yield was greater in C3 crops compared with C4 crops. Additionally, inbred and hybrid lines of rice and maize showed different sensitivities to O3 exposure. This study quantitatively demonstrates that C4 crops respond less to elevated [O3] than C3 crops. This understanding could help maintain cropland productivity in an increasingly polluted atmosphere.

Caffeine Produced in Rice Plants Provides Tolerance to Water-Deficit Stress

Exogenous or endogenous caffeine application confers resistance to diverse biotic stresses in plants. In this study, we demonstrate that endogenous caffeine in caffeine-producing rice (CPR) increases tolerance even to abiotic stresses such as water deficit. Caffeine produced by CPR plants influences the cytosolic Ca2+ ion concentration gradient. We focused on examining the expression of Ca2+-dependent protein kinase genes, a subset of the numerous proteins engaged in abiotic stress signaling. Under normal conditions, CPR plants exhibited increased expressions of seven OsCPKs (OsCPK10, OsCPK12, OsCPK21, OsCPK25, OsCPK26, OsCPK30, and OsCPK31) and biochemical modifications, including antioxidant enzyme (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase) activity and non-enzymatic antioxidant (ascorbic acid) content. CPR plants exhibited more pronounced gene expression changes and biochemical alterations in response to water-deficit stress. CPR plants revealed increased expressions of 16 OsCPKs (OsCPK1, OsCPK2, OsCPK3, OsCPK4, OsCPK5, OsCPK6, OsCPK9, OsCPK10, OsCPK11, OsCPK12, OsCPK14, OsCPK16, OsCPK18, OsCPK22, OsCPK24, and OsCPK25) and 8 genes (OsbZIP72, OsLEA25, OsNHX1, OsRab16d, OsDREB2B, OsNAC45, OsP5CS, and OsRSUS1) encoding factors related to abiotic stress tolerance. The activity of antioxidant enzymes increased, and non-enzymatic antioxidants accumulated. In addition, a decrease in reactive oxygen species, an accumulation of malondialdehyde, and physiological alterations such as the inhibition of chlorophyll degradation and the protection of photosynthetic machinery were observed. Our results suggest that caffeine is a natural chemical that increases the potential ability of rice to cope with water-deficit stress and provides robust resistance by activating a rapid and comprehensive resistance mechanism in the case of water-deficit stress. The discovery, furthermore, presents a new approach for enhancing crop tolerance to abiotic stress, including water deficit, via the utilization of a specific natural agent.

Climate variability, armed conflicts and child malnutrition in sub-saharan Africa: A spatial analysis in Ethiopia, Kenya and Nigeria

Background

Sub-Saharan Africa (SSA) has one of the highest prevalence of malnutrition among children under 5 in the world. It is also the region most vulnerable to the adverse effect of climate change, and the one that records the most armed conflicts. The chains of causality suggested in the literature on the relationship between climate change, armed conflict, and malnutrition have rarely been supported by empirical evidence for SSA countries.

Methods

This study proposes to highlight, under the hypothesis of spatial non-stationarity, the influence of climatic variations and armed conflicts on malnutrition in children under 5 in Ethiopia, Kenya, and Nigeria. To do this, we use spatial analysis on data from Demographic and Health Surveys (DHS), Uppsala Conflict Data Program Georeferenced Event Dataset (UCDP GED), Climate Hazards center InfraRed Precipitation with Station data (CHIRPS) and Moderate Resolution Imaging Spectroradiometer (MODIS).

Results

The results show that there is a spatial autocorrelation of malnutrition measured by the prevalence of underweight children in the three countries. Also, local geographically weighted analysis shows that armed conflict, temperature and rainfall are positively associated with the prevalence of underweight children in localities of Somali in Ethiopia, Mandera and Turkana of Wajir in Kenya, Borno and Yobe in Nigeria.

Conclusion

In conclusion, the results of our spatial analysis support the implementation of conflict-sensitive climate change adaptation strategies.

Drought response of water-conserving and non-conserving spring barley cultivars

Introduction

Breeding barley cultivars adapted to drought requires in-depth knowledge on physiological drought responses.

Methods

We used a high-throughput functional phenotyping platform to examine the response of four high-yielding European spring barley cultivars to a standardized drought treatment imposed around flowering.

Results

Cv. Chanell showed a non-conserving water-use behavior with high transpiration and maximum productivity under well-watered conditions but rapid transpiration decrease under drought. The poor recovery upon re-irrigation translated to large yield losses. Cv. Baronesse showed the most water-conserving behavior, with the lowest pre-drought transpiration and the most gradual transpiration reduction under drought. Its good recovery (resilience) prevented large yield losses. Cv. Formula was less conserving than cv. Baronesse and produced low yet stable yields. Cv. RGT's dynamic water use with high transpiration under ample water supply and moderate transpiration decrease under drought combined with high resilience secured the highest and most stable yields.

Discussion

Such a dynamic water-use behavior combined with higher drought resilience and favorable root traits could potentially create an ideotype for intermediate drought. Prospective studies will examine these results in field experiments and will use the newly gained understanding on water use in barley to improve process descriptions in crop simulation models to support crop model-aided ideotype design.

QTLs and Candidate Loci Associated with Drought Tolerance Traits of Kaybonnet x ZHE733 Recombinant Inbred Lines Rice Population

Rice is the most important staple crop for the sustenance of the world's population, and drought is a major factor limiting rice production. Quantitative trait locus (QTL) analysis of drought-resistance-related traits was conducted on a recombinant inbred line (RIL) population derived from the self-fed progeny of a cross between the drought-resistant tropical japonica U.S. adapted cultivar Kaybonnet and the drought-sensitive indica cultivar ZHE733. K/Z RIL population of 198 lines was screened in the field at Fayetteville (AR) for three consecutive years under controlled drought stress (DS) and well-watered (WW) treatment during the reproductive stage. The effects of DS were quantified by measuring morphological traits, grain yield components, and root architectural traits. A QTL analysis using a set of 4133 single nucleotide polymorphism (SNP) markers and the QTL IciMapping identified 41 QTLs and 184 candidate genes for drought-related traits within the DR-QTL regions. RT-qPCR in parental lines was used to confirm the putative candidate genes. The comparison between the drought-resistant parent (Kaybonnet) and the drought-sensitive parent (ZHE733) under DS conditions revealed that the gene expression of 15 candidate DR genes with known annotations and two candidate DR genes with unknown annotations within the DR-QTL regions was up-regulated in the drought-resistant parent (Kaybonnet). The outcomes of this research provide essential information that can be utilized in developing drought-resistant rice cultivars that have higher productivity when DS conditions are prevalent.

Frost Damage Index: The Antipode of Growing Degree Days

Abiotic stresses such as heat and frost limit plant growth and productivity. Image-based field phenotyping methods allow quantifying not only plant growth but also plant senescence. Winter crops show senescence caused by cold spells, visible as declines in leaf area. We accurately quantified such declines by monitoring changes in canopy cover based on time-resolved high-resolution imagery in the field. Thirty-six winter wheat genotypes were measured in multiple years. A concept termed "frost damage index" (FDI) was developed that, in analogy to growing degree days, summarizes frost events in a cumulative way. The measured sensitivity of genotypes to the FDI correlated with visual scorings commonly used in breeding to assess winter hardiness. The FDI concept could be adapted to other factors such as drought or heat stress. While commonly not considered in plant growth modeling, integrating such degradation processes may be key to improving the prediction of plant performance for future climate scenarios.

A multi-level approach reveals key physiological and molecular traits in the response of two rice genotypes subjected to water deficit at the reproductive stage

Rice is more vulnerable to drought than maize, wheat, and sorghum because its water requirements remain high throughout the rice life cycle. The effects of drought vary depending on the timing, intensity, and duration of the events, as well as on the rice genotype and developmental stage. It can affect all levels of organization, from genes to the cells, tissues, and/or organs. In this study, a moderate water deficit was applied to two contrasting rice genotypes, IAC 25 and CIRAD 409, during their reproductive stage. Multi-level transcriptomic, metabolomic, physiological, and morphological analyses were performed to investigate the complex traits involved in their response to drought. Weighted gene network correlation analysis was used to identify the specific molecular mechanisms regulated by each genotype, and the correlations between gene networks and phenotypic traits. A holistic analysis of all the data provided a deeper understanding of the specific mechanisms regulated by each genotype, and enabled the identification of gene markers. Under non-limiting water conditions, CIRAD 409 had a denser shoot, but shoot growth was slower despite better photosynthetic performance. Under water deficit, CIRAD 409 was weakly affected regardless of the plant level analyzed. In contrast, IAC 25 had reduced growth and reproductive development. It regulated transcriptomic and metabolic activities at a high level, and activated a complex gene regulatory network involved in growth-limiting processes. By comparing two contrasting genotypes, the present study identified the regulation of some fundamental processes and gene markers, that drive rice development, and influence its response to water deficit, in particular, the importance of the biosynthetic and regulatory pathways for cell wall metabolism. These key processes determine the biological and mechanical properties of the cell wall and thus influence plant development, organ expansion, and turgor maintenance under water deficit. Our results also question the genericity of the antagonism between morphogenesis and organogenesis observed in the two genotypes.

Metabolic pathways engineering for drought or/and heat tolerance in cereals

Drought (D) and heat (H) are the two major abiotic stresses hindering cereal crop growth and productivity, either singly or in combination (D/+H), by imposing various negative impacts on plant physiological and biochemical processes. Consequently, this decreases overall cereal crop production and impacts global food availability and human nutrition. To achieve global food and nutrition security vis-a-vis global climate change, deployment of new strategies for enhancing crop D/+H stress tolerance and higher nutritive value in cereals is imperative. This depends on first gaining a mechanistic understanding of the mechanisms underlying D/+H stress response. Meanwhile, functional genomics has revealed several stress-related genes that have been successfully used in target-gene approach to generate stress-tolerant cultivars and sustain crop productivity over the past decades. However, the fast-changing climate, coupled with the complexity and multigenic nature of D/+H tolerance suggest that single-gene/trait targeting may not suffice in improving such traits. Hence, in this review-cum-perspective, we advance that targeted multiple-gene or metabolic pathway manipulation could represent the most effective approach for improving D/+H stress tolerance. First, we highlight the impact of D/+H stress on cereal crops, and the elaborate plant physiological and molecular responses. We then discuss how key primary metabolism- and secondary metabolism-related metabolic pathways, including carbon metabolism, starch metabolism, phenylpropanoid biosynthesis, γ-aminobutyric acid (GABA) biosynthesis, and phytohormone biosynthesis and signaling can be modified using modern molecular biotechnology approaches such as CRISPR-Cas9 system and synthetic biology (Synbio) to enhance D/+H tolerance in cereal crops. Understandably, several bottlenecks hinder metabolic pathway modification, including those related to feedback regulation, gene functional annotation, complex crosstalk between pathways, and metabolomics data and spatiotemporal gene expressions analyses. Nonetheless, recent advances in molecular biotechnology, genome-editing, single-cell metabolomics, and data annotation and analysis approaches, when integrated, offer unprecedented opportunities for pathway engineering for enhancing crop D/+H stress tolerance and improved yield. Especially, Synbio-based strategies will accelerate the development of climate resilient and nutrient-dense cereals, critical for achieving global food security and combating malnutrition.

Investigating the influence of elevated temperature on nutritional and yield characteristics of mung bean (Vigna radiata L.) genotypes during seed filling in a controlled environment

Rising temperatures impact different developmental stages of summer crops like mung bean, particularly during the crucial seed-filling stage. This study focused on two mung bean genotypes, categorized as heat-tolerant [HT] or heat-sensitive [HS]. These genotypes were grown in pots in an outdoor natural environment (average day/night temperature 36°C/24.3°C) until the onset of podding (40 days after sowing) and subsequently relocated to controlled-environment walk-in growth chambers for exposure to heat stress (42°C/30°C) or control conditions (35°C/25°C) until maturity. For all measured attributes, heat stress had a more pronounced effect on the HS genotype than on the HT genotype. Heat-stressed plants exhibited severe leaf damage, including membrane damage, reduced chlorophyll content, diminished chlorophyll fluorescence, and decreased leaf water content. Heat stress impeded the seed-filling rate and duration, decreasing starch, protein, fat, and mineral contents, with a notable decline in storage proteins. Heat stress disrupted the activities of several seed enzymes, inhibiting starch and sucrose accumulation and consequently decreasing individual seed weights and seed weight plant-1. This study revealed that heat stress during seed filling severely impaired mung bean seed yield and nutritional quality due to its impact on various stress-related traits in leaves and enzyme activities in seeds. Moreover, this research identified potential mechanisms related to heat tolerance in genotypes with contrasting heat sensitivity.

Understanding the effect of heat stress during seed filling on nutritional composition and seed yield in chickpea (Cicer arietinum L.)

Increasing temperature affects all food crops, thereby reducing their yield potential. Chickpea is a cool-season food legume vital for its nutritive value, but it is sensitive to high temperatures (> 32/20 °C maximum/minimum) during its reproductive and seed-filling stages. This study evaluated the effects of heat stress on yield and qualitative traits of chickpea seeds in a controlled environment. Chickpea genotypes differing in heat sensitivity [two heat-tolerant (HT) and two heat-sensitive (HS)] were raised in pots, initially in an outdoor environment (average 23.5/9.9 °C maximum/minimum), until the beginning of pod set (107-110 days after sowing). At this stage, the plants were moved to a controlled environment in the growth chamber to impose heat stress (32/20 °C) at the seed-filling stage, while maintaining a set of control plants at 25/15 °C. The leaves of heat-stressed plants of the HT and HS genotypes showed considerable membrane damage, altered stomatal conductance, and reduced leaf water content, chlorophyll content, chlorophyll fluorescence, and photosynthetic ability (RuBisCo, sucrose phosphate synthase, and sucrose activities) relative to their corresponding controls. Seed filling duration and seed rate drastically decreased in heat-stressed plants of the HT and HS genotypes, severely reducing seed weight plant-1 and single seed weight, especially in the HS genotypes. Yield-related traits, such as pod number, seed number, and harvest index, noticeably decreased in heat-stressed plants and more so in the HS genotypes. Seed components, such as starch, proteins, fats, minerals (Ca, P, and Fe), and storage proteins (albumin, globulins, glutelin, and prolamins), drastically declined, resulting in poor-quality seeds, particularly in the HS genotypes. These findings revealed that heat stress significantly reduced leaf sucrose production, affecting the accumulation of various seed constituents, and leading to poor nutritional quality. The HT genotypes were less affected than the HS genotypes because of the greater stability of their leaf water status and photosynthetic ability, contributing to better yield and seed quality traits in a heat-stressed environment.

Spermidine enhances heat tolerance of rice seeds during mid-filling stage and promote subsequent seed germination

Introduction

Heat stress is a vital factor which restricts rice seed quality and yield. However, the response mechanism to heat stress in the mid filling stage of rice seed is unclear.

Methods

In the present study we integrated phenotypic analysis with biochemical, hormone, and gene expression analysis in order to explore technologies for improving rice seeds heat tolerance and subsequent seed germination.

Results

Spermidine (Spd) application effectively alleviated the damage of heat stress treatment during mid-filling stage (HTM, 12-20 days after pollination) on seed development, promoted subsequent seed germination and seedlings establishment. Spd significantly increased seed dry weight, starch and amylose contents during seed development under heat stress, and improved seed germinate, seedlings establishment and seedling characteristics during germination time. Biochemical analysis indicated that, HTM significantly decreased the activities of several starch synthase enzymes and led to a decrease in starch content. While Spd treatment significantly enhanced the activities of ADP-glucose pyrophosphorylas and granule-bound starch synthase, as well as the corresponding-genes expressions in HTM rice seeds, resulting in the increases of amylose and total starch contents. In addition, Spd significantly increased the catalase and glutathione reductase activities together with corresponding-genes expressions, and lowered the overaccumulation of H2O2 and malondialdehyde in HTM seeds. In the subsequent seed germination process, HTM+Spd seeds exhibited dramatically up-regulated levels of soluble sugars, glucose, ATP and energy charges. Consistently, HTM+Spd seeds showed significantly increased of α-amylose and α-glucosidase activities as well as corresponding-genes expressions during early germination. Moreover, HTM evidently increased the abscisic acid (ABA) content, decreased the gibberellin (GA) content, and accordingly significantly declined the GA/ABA ratio during early rice seeds germination. However, Spd treatment did not significantly affect the metabolism of GA and ABA in seed germination stage.

Discussion

The present study suggested that Spd treatment could effectively alleviate the negative impact of HTM on seed development and the subsequent seed germination, which might be closely correlated with starch synthesis and antioxidant defense during seed filling period, starch decomposition and energy supply in seed germination period.

Nutrient management: as a panacea to improve the caryopsis quality and yield potential of durum wheat (Triticum turgidum L.) under the changing climatic conditions

The increasing human population and the changing climate, which have given rise to frequent drought spells, pose a serious threat to global food security, while identification of high-yielding drought-tolerant genotypes coupled with nutrient management remains a proficient approach to cope with these challenges. An increase in seasonal temperature, recurring drought stress, and elevated atmospheric CO2 are alarmingly affecting durum wheat production, productivity, grain quality, and the human systems it supports. An increase in atmospheric carbon dioxide can improve wheat grain yield in a certain amount, but the right amount of nutrients, water, and other required conditions should be met to realize this benefit. Nutrients including nitrogen, silicon, and sulfur supply could alleviate the adverse effects of abiotic stress by enhancing antioxidant defense and improving nitrogen assimilation, although the effects on plant tolerance to drought stress varied with nitrogen ionic forms. The application of sewage sludge to durum wheat also positively impacts its drought stress tolerance by triggering high accumulation of osmoregulators, improving water retention capacity in the soil, and promoting root growth. These beneficial effect of nutrients contribute to durum wheat ability to withstand and recover from abiotic stress conditions, ultimately enhance its productivity and resilience. While these nutrients can provide benefits when applied in appropriate amounts, their excessive use can lead to adverse environmental consequences. Advanced technologies such as precision nutrient management, unmanned aerial vehicle-based spraying, and anaerobic digestion play significant roles in reducing the negative effects associated with nutrients like sewage sludge, zinc, nanoparticles and silicon fertilizers. Hence, nutrient management practices offer significant potential to enhance the caryopsis quality and yield potential of durum wheat. Through implementing tailored nutrient management strategies, farmers, breeders, and agronomists can contribute to sustainable durum wheat production, ensuring food security and maintaining the economic viability of the crop under the changing climatic conditions.

Genes and pathways correlated with heat stress responses and heat tolerance in maize kernels

Global warming leads to frequent extreme weather, especially the extreme heat events, which threating the safety of maize production. Here we selected a pair of maize inbred lines, PF5411-1 and LH150, with significant differences in heat tolerance at kernel development stage. The two maize inbred lines were treated with heat stress at kernel development stage. Compared with the control groups, transcriptomic analysis identified 770 common up- and down-regulated genes between PF5411-1 and LH150 under heat stress conditions, and 41 putative TFs were predicted. Based on the interaction term of the two-factorial design, we also identified 6,744 differentially regulated genes between LH150 and PF5411-1, 111 common up-regulated and 141 common down-regulated genes were overlapped with the differentially regulated genes, respectively. Combined with proteins and metabolites data, several key pathways including seven differentially regulated genes were highly correlated with the heat tolerance of maize kernels. The first is the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway ko04141: protein processing in endoplasmic reticulum, four small heat shock protein (sHSP) genes were enriched in this pathway, participating with the process of ER-associated degradation (ERAD). The second one is the myricetin biosynthesis pathway, a differentially regulated protein, flavonoid 3',5'-hydroxylase [EC:1.14.14.81], catalyzed the synthesis of myricetin. The third one is the raffinose metabolic pathway, one differentially regulated gene encoded the raffinose synthase controlled the synthesis of raffinose, high level of raffinose enhances the heat tolerance of maize kernels. And the last one is the ethylene signaling pathway. Taken together, our work identifies many genes responded to heat stress in maize kernels, and finds out seven genes and four pathways highly correlated with heat tolerance of maize kernels.

Responses to water stress extremes in diverse red clover germplasm accessions

Red clover (Trifolium pratense L.), a key perennial pastoral species used globally, can strengthen pastural mixes to withstand increasingly disruptive weather patterns from climate change. Breeding selections can be refined for this purpose by obtaining an in-depth understanding of key functional traits. A replicated randomized complete block glasshouse pot trial was used to observe trait responses critical to plant performance under control (15% VMC), water deficit (5% VMC) and waterlogged conditions (50% VMC) in seven red clover populations and compared against white clover. Twelve morphological and physiological traits were identified as key contributors to the different plant coping mechanisms displayed. Under water deficit, the levels of all aboveground morphological traits decreased, highlighted by a 41% decrease in total dry matter and 50% decreases in both leaf number and leaf thickness compared to the control treatment. An increase in root to shoot ratio indicated a shift to prioritizing root maintenance by sacrificing shoot growth, a trait attributed to plant water deficit tolerance. Under waterlogging, a reduction in photosynthetic activity among red clover populations reduced several morphological traits including a 30% decrease in root dry mass and total dry matter, and a 34% decrease in leaf number. The importance of root morphology for waterlogging was highlighted with low performance of red clover: there was an 83% decrease in root dry mass compared to white clover which was able to maintain root dry mass and therefore plant performance. This study highlights the importance of germplasm evaluation across water stress extremes to identify traits for future breeding programs.