Heat Tolerant Genotypes Research Articles

Evaluation of heat tolerance potential in Capsicum annum L. genotypes under heat stress

Summer vegetables are severely affected by high temperature above threshold level which ultimately results in serious losses of their production. To cope with these economic losses different strategies had been adopted. The present study was designed to screen out heat tolerant genotypes of bell pepper. For this purpose, experiment was conducted in plant growth room in Institute of Horticultural Sciences, University of Agriculture Faisalabad. Ten genotypes of bell pepper (C1G3, C3G5, C7G4, V6G4, C2-E, C5G4, C43-D, C4G3, C43-A, C2G3) were brought from Ayub Agriculture Research Institute Faisalabad (AARI) and were grown. Heat treatment up to 40 ̊C was given. Data regarding agronomic traits (number of leaves, root length, shoot length, seedling dry weight, seedling fresh weight, electrolyte leakage) and physiological (Stomatal conductance, photosynthetic rate, transpiration rate and water use efficiency) was collected. Proper statistical designs were used to analyze the data. The research findings proved that heat stress significantly affected physiology, morphology and mechanisms of screened genotypes which followed the order for the heat stress as C5G4, C1G3, C2G3, C43-A, C3G5, C43-D, V6G4, C4G3, C43-A and C2G3, respectively. The collective effects of all these changes under high temperature stress resulted in poor plant growth and productivity. On the basis of physical and physiological parameters, genotypes C5G4, C1G3 and C43-A were among the most tolerant group and the most resistant genotypes.

Heat stress elicits remodeling in the anther lipidome of peanut

Understanding the changes in peanut (Arachis hypogaea L.) anther lipidome under heat stress (HT) will aid in understanding the mechanisms of heat tolerance. We profiled the anther lipidome of seven genotypes exposed to ambient temperature (AT) or HT during flowering. Under AT and HT, the lipidome was dominated by phosphatidylcholine (PC), phosphatidylethanolamine (PE), and triacylglycerol (TAG) species (> 50% of total lipids). Of 89 lipid analytes specified by total acyl carbons:total carbon–carbon double bonds, 36:6, 36:5, and 34:3 PC and 34:3 PE (all contain 18:3 fatty acid and decreased under HT) were the most important lipids that differentiated HT from AT. Heat stress caused decreases in unsaturation indices of membrane lipids, primarily due to decreases in highly-unsaturated lipid species that contained 18:3 fatty acids. In parallel, the expression of Fatty Acid Desaturase 3-2 (FAD3-2; converts 18:2 fatty acids to 18:3) decreased under HT for the heat-tolerant genotype SPT 06-07 but not for the susceptible genotype Bailey. Our results suggested that decreasing lipid unsaturation levels by lowering 18:3 fatty-acid amount through reducing FAD3 expression is likely an acclimation mechanism to heat stress in peanut. Thus, genotypes that are more efficient in doing so will be relatively more tolerant to HT.

Evaluation of bread wheat (Triticum aestivum L.) for terminal heat tolerance

Terminal heat tolerance of 34 wheat genotypes were analyzed for two years. Among 14 traits, canopy temperature, plot yield and days to heading were major components in clustering of genotypes. Three genotypes viz., DBW39, DBW16 and DBW14 had lowest HSI (0.34-0.36) for plot yield and were considered as heat tolerant genotypes by, both, HCA (Hierarchical Cluster Analysis) as well as DA (Discriminant Analysis). These genotypes may serve as potential donors in wheat breeding to improve the terminal heat tolerance.

Assessment of terminal heat tolerance based on agro-morphological and stress selection indices in wheat

A study was conducted to quantify the effects of terminal heat stress on yield and component traits for two consecutive years under normal and late sown environments. Analysis of variance indicated significant differences among genotypes for most of the studied traits. Tiller/meter (T/M) and grain yield were the most affected traits (>30% reduction), whereas traits like grain filling rate (GFR), grain number per spike (GNPS) and thousand kernel weight (TKW) were less affected (<15%) under heat stress. The traits, viz. GFR, GNPS, TKW, T/M and spike weight, as well as the relative change in these traits exhibited positive and significant correlation with yield and yield stability index (YSI), while negative and significant correlation with heat susceptibility index (HSI) and kernel weight reduction percentage (KWR) under heat stress. Based on HSI, KWR, and YSI indices, genotypes WH 1021, NW 1014 and NW 2036 were identified as the heat tolerant, while HD 3086, HD 2967 and HD 3059 were identified to be highly productive under both normal and heat stress environments based on STI and mean yield across the environments. The above selected genotypes also showed high mean performance for GFR and TKW under heat stress and could be used for breeding wheat genotypes for heat tolerance.

Exploration of Heat Stress-Responsive Markers in Understanding Trait Associations in Wheat

Heat stress (HS) is detrimental to wheat production and productivity globally. To combat HS, several genetic, molecular, and genomic approaches have been employed in the past. Analyzing the physiochemical mechanisms and the important regulatory genes involved is the key to develop HS tolerant plants. In the present work, a total of 243 novel simple sequence repeat (SSR) markers developed from stress-associated genes identified through RNA-seq were used for understanding marker–trait associations. 37 SSRs were found to be clearly polymorphic and among these, 28 SSR loci were significantly associated with component traits of HS tolerance. The polymorphic SSRs were validated for diversity analysis on a subset of 85 genotypes. The genotypes were grouped into four clusters representing diverse and similar alleles imparting HS tolerance in Indian and exotic genotypes. Additionally, 28 genes selected for the expression analysis confirmed that 15 genes were induced under HS in the thermotolerant WH1021 and Raj3765 and repressed in thermosusceptible HD2009 cultivar. Hence, the information on traits associated with candidate genes and the SSR markers overlying on the gene will enhance our understanding of thermotolerance mechanism operating in wheat and will help the breeders in the precise development of heat-tolerant genotypes through marker-assisted selection (MAS).

Genetic and Agro-morphological diversity in global barley (Hordeum vulgare L.) collection at ICARDA

Heat stress at later growth stage is one of the major limitations in achieving potential yield in barley. Incorporation of heat tolerance in the variety development process is an essential task that breeders would like to achieve by exploring new sources of genetic variability and their utilization. A better understanding of genetic variation in existing genotypes under heat stress is required to produce high yielding varieties with improved heat tolerance. An association mapping panel 2017 (AM2017), comprising of 316 genotypes, was evaluated under timely and late sown (heat stress) conditions for two consecutive crop seasons at Hisar in India during 2017–2019. Eight agro-morphological traits, mainly contributing to yield, were considered agro-morphological diversity study. Genetic diversity and population structure were explored by using the 50 K iSelect Illumina Barley SNP array. A set of 36,793 SNP markers, covering a genetic distance of 991.82 cM with an average marker density of 37.09 SNPs/cM, was obtained after quality filtration. The gene diversity (GD) and Polymorphic Information Content (PIC) at genome level was 0.362 and 0.289, respectively. In AM2017, two subpopulations were observed mainly due to the row types. Principal component analysis of agro-morphological traits revealed that days to heading and maturity along with spike length, spikelet number per spike and grain yield per plot were the most important traits in timely and late sown conditions. The information on agro-morphological genetic diversity under heat stress conditions will be useful in identifying heat tolerant genotypes for use in barley breeding programs.

Identification and expression analysis of Cathepsin B-like protease 2 genes in tomato at abiotic stresses especially at High temperature

Cathepsin B-like protease 2 (CathB2) genes have been shown to participate in programmed cell death (PCD) that is a crucial component of development and defense mechanisms in plants at biotic and abiotic stresses. However, little is known regarding CathB2 genes in tomato. In this study, we reported the analysis of two SlCathB2 genes named SlCathB2−1 and SlCathB2−2. Promoter analysis found some elements related to abiotic stress-responses in two SlCathB2 genes. Domain analysis revealed that SlCathB2 encoding proteins characterized by signal peptide, propeptide, and papain family cysteine protease domain. The phylogenetic analysis revealed their close evolutionary relationship with the CathB2 of Solanum tuberosum. Expression analysis showed that SlCathB2 differentially expressed in various tissues and SlCathB2 positively responded to high temperature, drought, salt, ABA and SA treatments with higher expression upon high-temperature stress (HS) in the cultivated tomato line ‘LA1698′ (Solanum lycopersicum) and the currant tomato line ‘LA2093′ (Solanum pimpinellifolium). Then, the expression of SlCathB2 in the leaves of tomato genotypes with different thermotolerance under moderately elevated temperature (MET, 33 °C/33 °C) and acutely elevated temperature (AET, 40 °C/40 °C) stresses were further analyzed. The results showed that SlCathB2 genes were most triggered in heat-sensitive tomato genotypes (S1 and S2) as compared to heat-tolerant genotypes (T1 and T2) and were not significantly induced in the moderate genotypes (M1 and M2) under MET and AET stresses, suggesting that they were negatively regulated by HS. Furthermore, SlCathB2 genes showed similar expression patterns in tomato genotypes with same behavior for thermotolerance under MET and AET stresses, while exhibited higher expression level under AET stress, indicating that more thermosensors and multiple HSR (high-temperature stress- responsive) pathways were activated under AET stress leading to the higher expression level of a set of HSR genes including SlCathB2−1 and SlCathB2−2 genes. This study lays a foundation for functional studies of SlCathB2 in tomato.

Indices based on culm-leaf growth, spike-grain development and relative yield for identification of heat tolerant genotypes in triticale and wheat

Indices based on culm-leaf growth, spike-grain development and relative yield for identification of heat tolerant genotypes in triticale and wheat

Identification and Characterization of Contrasting Genotypes/Cultivars for Developing Heat Tolerance in Agricultural Crops: Current Status and Prospects.

Rising global temperatures due to climate change are affecting crop performance in several regions of the world. High temperatures affect plants at various organizational levels, primarily accelerating phenology to limit biomass production and shortening reproductive phase to curtail flower and fruit numbers, thus resulting in severe yield losses. Besides, heat stress also disrupts normal growth, development, cellular metabolism, and gene expression, which alters shoot and root structures, branching patterns, leaf surface and orientation, and anatomical, structural, and functional aspects of leaves and flowers. The reproductive growth stage is crucial in plants’ life cycle, and susceptible to high temperatures, as reproductive processes are negatively impacted thus reducing crop yield. Genetic variation exists among genotypes of various crops to resist impacts of heat stress. Several screening studies have successfully phenotyped large populations of various crops to distinguish heat-tolerant and heat-sensitive genotypes using various traits, related to shoots (including leaves), flowers, fruits (pods, spikes, spikelets), and seeds (or grains), which have led to direct release of heat-tolerant cultivars in some cases (such as chickpea). In the present review, we discuss examples of contrasting genotypes for heat tolerance in different crops, involving many traits related to thermotolerance in leaves (membrane thermostability, photosynthetic efficiency, chlorophyll content, chlorophyll fluorescence, stomatal activity), flowers (pollen viability, pollen germination, fertilization, ovule viability), roots (architecture), biomolecules (antioxidants, osmolytes, phytohormones, heat-shock proteins, other stress proteins), and “omics” (phenomics, transcriptomics, genomics) approaches. The traits linked to heat tolerance can be introgressed into high yielding but heat-sensitive genotypes of crops to enhance their thermotolerance. Involving these traits will be useful for screening contrasting genotypes and would pave the way for characterizing the underlying molecular mechanisms, which could be valuable for engineering plants with enhanced thermotolerance. Wherever possible, we discussed breeding and biotechnological approaches for using these traits to develop heat-tolerant genotypes of various food crops.

EVALUATION OF COTTON (GOSSYPIUM SPP.) GERMPLASM FOR HEAT TOLERANCE UNDER NORMAL AND LATE PLANTING TIME

The objective of this study was to determine cotton (Gossypium ssp.) germplasm for heat tolerance under normal and late planting time. For this aiming 200 cotton genotypes and five check varieties (Gloria, SG 125, Flash, Ozbek 105 and Candia) were evaluated under two different temperature regimes and experiments were conducted according to the augmented design with four blocks. Field studies were carried out at the GAP International Agricultural Research and Training Center’s experimental area in Diyarbakır, Turkey, in 2016 cotton growing season. In the study heat susceptibility index was used for discriminate to the genotypes for heat tolerance. Genotypes were classified into four groups based on the heat susceptibility index. The results of this study indicated that five cotton genotypes (TAM 139-17 ELS, CIM-240, Haridost, MNH-990 and AzGR-11835) were in highly heat tolerant, 28 genotypes were found heat tolerant, 56 genotypes were in the moderately heat tolerant and other 120 genotypes were observed susceptible for heat tolerance. Based on the heat susceptibility index, five cotton genotypes can be used as parent for heat tolerance improvement in the cotton breeding program where high temperature is a limiting factor for seed cotton yield.

Genetic relationship among selected heat and drought tolerant bread wheat genotypes using SSR markers, agronomic traits and grain protein content

ABSTRACT Assessing the genetic variation and relationships present in crop germplasm is a pre-requisite for parental selection and breeding. The objective of this study was to determine the genetic relationships present among selected heat and drought tolerant wheat genotypes using simple sequence repeat (SSR) markers, agronomic traits and grain quality parameters to select desirable parents for breeding. Twenty-four agronomically selected wheat genotypes sourced from the International Maize and Wheat Improvement Centre (CIMMYT)’s heat and drought tolerance nursery and four local check varieties were genotyped using 12 selected polymorphic SSR markers. The test genotypes were phenotyped using yield and yield-component traits, and grain protein content (GPC) under non-stressed (NS) and drought-stressed (DS) conditions. Expected heterozygosity mean value of 0.58 indicated moderate genetic diversity for breeding. The studied wheat genotypes were delineated into six genetic groups using cluster analysis. Significant genotypic differences were observed for agronomic traits and GPC under NS and DS conditions. Genetically unrelated breeding parents including LM02, LM13, LM23, LM41, LM44, LM71, LM73 and LM75 were selected for population development and breeding for enhanced grain yield and protein content under heat and drought-stressed environments.

Identification of suitable trait index for selection of heat tolerant wheat (Triticum aestivum) genotypes

Terminal heat stress is one of the major production constraints in wheat-producing areas of south-east Asia. The selection of genotypes based on grain yield per se is not effective under stress condition. In the present study 30 wheat (Triticum aestivum L.) genotypes were evaluated under normal and heat stress conditions during 2016-17 and 2017-18 to determine the suitable trait index for selection of genotypes under non-stress and heat stress environments and identification of heat tolerant genotypes. The observation was recorded for 13 morphological, biochemical and physiological traits. The index based on seven characters like grain yield, days to heading, biological yield, green fodder yield, dry matter content, catalase and peroxidase was most suitable with the genetic gain of 4856.09% and the genetic advancement of 33.09 in normal condition and the index based on five characters comprising days to heading, biological yield, number of tillers, catalase and peroxidase was most suitable with an expected genetic gain of 20101.32% and genetic advance of 35.09. The genotypes RAJ 3765, BRW 3794, HD 2643, SW 129, DBW 14, SW 160, BRW 3759, BRW 3762 and BRW 3800 were identified as moderately tolerant considering selection index score and heat susceptibility index. These genotypes may be promoted for cultivation under late sown conditions and used as parents for the development of genotypes tolerant to terminal heat stress.

Heat tolerance in vegetables in the current genomic era: an overview

Global temperature rise is emerging as an alarming threat to agriculture and especially for vegetables, as they are more sensitive to high temperature because of their succulent nature. Vegetables include different edible plant parts such as leaves, stems, stalks, roots, tubers, bulbs, flowers, fruits, and seeds. An increase in temperature impairs the growth and development of vegetable plants and eventually reduces their yield. Heat tolerance is a complex quantitative trait that involves a series of physiological, biochemical, and molecular pathways. This complexity is further exacerbated by the presence of a large magnitude of genotype × environment and epistatic interactions, so breeders have to face challenges during development and selection of heat tolerant genotypes. Understanding the response of plants and resistance mechanisms involved in heat tolerance would help the breeders in formulating strategies to improve vegetable productivity under heat stress. In this review, firstly the impact of heat stress on the morphological, physiological, and molecular processes of different vegetables have been described, then discussed adaptation mechanisms employed by plants to combat heat stress. Finally, conventional and potential genomic strategies i.e. marker-assisted breeding, quantitative trait loci mapping, genome wide association, genomic selection, genetic engineering, and genome editing that are being used by the breeders to create heat resistance are presented. For vegetables, genome editing, and transgenic approaches need to be combined with conventional and marker-assisted breeding activities to develop heat tolerant varieties as these efforts will lead to tangible practical outcomes that will improve the vegetable productivity.

Cell Membrane Stability and Relative Cell Injury in Response to Heat Stress during Early and Late Seedling Stages of Diverse Carrot (Daucus carota L.) Germplasm

Heat waves occur with more regularity and they adversely affect the yield of cool season crops including carrot (Daucus carota L.). Heat stress influences various biochemical and physiological processes including cell membrane permeability. Ion leakage and increase in cell permeability are indicators of cell membrane stability and have been used to evaluate the stress tolerance response in numerous crops and inform plant breeders for improving heat tolerance. No study has been published about the effects of heat stress on cell membrane stability and relative cell injury of carrot. Therefore, the present study was designed to estimate these stress indicators in response to heat stress at the early and late seedling developmental stages of 215 diverse accessions of wild and cultivated carrot germplasm. The article identifies the relationship between early and late stages of seedling tolerance across carrot genotypes and identifies heat-tolerant genotypes for further genetic analysis. Significant genetic variation among these stress indicators was identified with cell membrane stability and relative cell injury ranging from 6.3% to 97.3% and 2.8% to 76.6% at the early seedling stage, respectively; whereas cell membrane stability and relative cell injury ranged from 2.0% to 94.0% and 2.5% to 78.5%, respectively, at the late seedling stage under heat stress. Broad-sense heritability ranged from 0.64 to 0.91 for traits of interest under study, which indicates a relatively strong contribution of genetic factors in phenotypic variation among accessions. Heat tolerance varied widely among both wild and cultivated accessions, but the incidence of tolerance was higher in cultivated carrots than in wild carrots. The cultivated carrot accessions PI 326009 (Uzbekistan), PI 451754 (Netherlands), L2450 (USA), and PI 502654 (Pakistan) were identified as the most heat-tolerant accessions with highest cell membrane stability. This is the first evaluation of cell membrane stability and relative cell injury in response to heat stress during carrot development.

Possible involvement of xanthophyll cycle pigments in heat tolerance of chickpea (Cicer arietinum L.)

Chickpea being a winter season crop often experiences heat stress during reproductive phase. For chickpea production, terminal heat stress is one of the major constraints. Plants have built up numerous mechanisms to combat the heat stress. We considered the photosynthetic pigments for heat tolerance. Therefore, in order to investigate the heat tolerance in relation to photosynthetic pigments, a field trial was carried out having 4 contrasting genotypes namely BG 240 and JG 14 (relatively heat tolerant), SBD 377 (moderately tolerant) and ICC 1882 (relatively heat sensitive). Heat stress was imposed by altering the sowing date i.e. normal (18th November) and late sown (18th December). Under delayed sown condition, heat stress was faced by crop starting from flowering stage to crop maturity. Under heat stress condition, heat tolerant genotypes BG 240 and JG 14 maintained higher level of membrane stability, RWC (%), osmolytes, dry matter partitioning, grain yield, heat tolerance index and had higher values of zeaxanthin, quantum yield of PS II (Fv/Fm ratio), non-photochemical quenching (NPQ), photosynthetic rate, level of photosynthetic pigments (chlorophylls and carotenoids) and lower level of violaxanthin, and lipid peroxidation as compared to heat sensitive one (ICC 1882). In addition to this, Fv/Fm ratio and NPQ exhibited positive relationship with heat tolerance which suggested the involvement of xanthophyll cycle pigments in chickpea heat tolerance.

Genetic diversity of sugar beet under heat stress and deficit irrigation

AbstractIn the light of climate changes and global warming, as well as the rapid expansion in sugar beet (Beta vulgaris L.) cultivation in Egypt, the development of sugar beet varieties with improved tolerance to high temperature and deficit irrigation is of great importance. The objective of this study was to evaluate sugar beet genotypes under high temperatures and deficit irrigation conditions for further identification and selection of heat and drought tolerant genotypes. In the current study, a panel of 18 sugar beet breeding lines produced at the USDA–ARS–NWISRL, Kimberly, ID, and the commercial sugar beet cultivar Kawimera were evaluated for yield and quality under high temperature. Six promising lines in terms of yield and quality were further evaluated under both high temperature and deficit irrigation for two growing seasons.All lines performed differently under deficit irrigation, indicating a high degree of genetic variability in the evaluated lines. Additionally, yield traits showed negative effect due to deficit irrigation. A significant positive correlation was observed between stress tolerance index (STI), and average root and sugar yields under stressed and non‐stressed conditions. A linear relationship between STI and average root and sugar yields indicates that STI is a reliable stress index to select high yielding genotypes under both optimum‐ and deficit‐irrigation conditions. USKPS25 and USC944‐6‐68 breeding lines are most likely adapted to deficit irrigation and high temperature and suitable to be utilized in the proposed sugar beet breeding programs in Egypt.

Wheat Variety Improvement for Climate Resilience

High temperature stress unfavorably affects plant growth and reduces grain yield (GY). This study was conducted with an aim to identify the terminal heat tolerance of one hundred and two wheat genotypes with three checks. They were sown under normal (non-stress) and late (stress) conditions at Regional Agricultural Research Station (RARS), Tarahara; RARS, Nepalgunj and National Wheat Research Program (NWRP), Bhairahawa, Nepal. The trial was sown in Augmented design during 2014/15 winter season as a Nepal heat tolerance wheat screening nursery (NHTWSN). Grain yield, maturity, stress susceptibility and tolerant indices were estimated to assess the heat tolerance of the genotypes. Combined analysis among the tested wheat lines (102 new entries + 3 checks) showed that KACHU//KIRITATI/WBLL1 ((Heat tolerance index (HTI) = 1.78) possessed the highest level of heat tolerance, followed by SLVS /3/ CROC_1/ AE.SQUARROSA (224)// OPATA/5/ VEE/LIRA//BOW/3/BCN/4/KAUZ/6/ 2*KA/NAC//TRCH (HTI=1.57) while SUP152/VILLA JUAREZ F2009 (HTI=0.83) appeared to be the least heat tolerant. Correlation analysis showed that yield under stress environment had positive (r=0.083) and significant (p&lt;0.05) association with that of non-stress environment. Grain yield (Kg/ha) under both environments had significant positive correlation with mean productivity (MP), geometric mean productivity (GMP) and HTI. Thirty seven wheat genotypes possessing heat tolerance will be considered in further heat tolerance trial and can also be used directly in varietal development and in the crossing program to breed more heat tolerant genotypes.

Morphological and Ultra-Structural Characterization of Blackgram [Vigna mungo (L.) Hepper] Genotypes Grown under High Temperature Stress

Background: In this decade, increasing temperatures and adverse environmental factors are expected to influence the crop yield, seed quality and germination ability. Prolonged heat stress affects the pod setting, seed morphology and alters the starch granules.Methods: In this study, Scanning Electron Microscopy (SEM) and Light microscope was used to investigate the variations of morphological and ultra-structural characteristics in blackgram genotypes grown under high temperature (38+2°C) stress (HTS). Nineteen blackgram genotypes were evaluated under open top temperature controlled chamber (OTC) and the genotypes were classified into three categories such as heat tolerant, moderately heat tolerant and heat susceptible genotypes based on the Temperature Induction Response (TIR) and yield reduction percentage under HTS. Two genotypes were selected and examined the seed size, surface pattern, starch granule size and hilum from the each category.Result: Seed coat morphology was captured using SEM and light microscope showed that the tolerant genotype VBG-07-001 had a clear shiny surface, thin and reduced cotyledon fissures, compact surface devoid of surface deposits and pits whereas rest of the genotypes (VBG-06-001, VBN-6, CoBg-11-02, CoBg-11-03 and VBG-08-003) had a rough surface. A bold and well-structured starch granule was observed in heat tolerant lines whereas, unstructured and pleated granules were observed in moderately tolerant and heat stress lines. These morphological and ultra-structural studies revealed remarked diversity among different genotypes that can be regarded as useful to screen the genotypic tolerant characters for HTS.

Heat Tolerance in Sugarcane: Optimum Temperature and Phenological Stage to Determination of Thermotolerance as Selection Criteria

Heat stress is the major abiotic stressor in agriculture which reduces crop productivity and yield. Six sugarcane (Sacharum officinarum L.) genotypes were studied to investigate the impact of three temperature levels at four phenological stages on tissue electrolyte production and the feasibility of using the cell thermostability method (CTM) for the identification and selection of heat tolerant sugarcane genotypes. The cell membrane thermostability was quantified by measuring relative cell injury percentage with a modification in the temperature treatment on four phenological stages in a field experiment. Our results suggest that heat tolerance based on cell membrane thermostability can be improved using the existing genetic variability available within the commercial or experimental sugarcane germplasm. We conclude that the cell membrane thermostability test can be a useful screening procedure for selecting sugarcane genotypes that tolerate high temperature stress. The test can be used in conjunction with a temperature trait of 60 &amp;deg;C during the maturity stage. This procedure predicts the ability of sugarcane genotypes to maintain yield and juice quality under stressful field conditions.

Effect of Heat Stress on Seed Protein Composition and Ultrastructure of Protein Storage Vacuoles in the Cotyledonary Parenchyma Cells of Soybean Genotypes That Are Either Tolerant or Sensitive to Elevated Temperatures.

High growth temperatures negatively affect soybean (Glycine max (L.) Merr) yields and seed quality. Soybean plants, heat stressed during seed development, produce seed that exhibit wrinkling, discoloration, poor seed germination, and have an increased potential for incidence of pathogen infection and an overall decrease in economic value. Soybean breeders have identified a heat stress tolerant exotic landrace genotype, which has been used in traditional hybridization to generate experimental genotypes, with improved seed yield and heat tolerance. Here, we have investigated the seed protein composition and ultrastructure of cotyledonary parenchyma cells of soybean genotypes that are either susceptible or tolerant to high growth temperatures. Biochemical analyses of seed proteins isolated from heat-tolerant and heat-sensitive genotypes produced under 28/22 °C (control), 36/24 °C (moderate), and 42/26 °C (extreme) day/night temperatures revealed that the accumulation in soybean seeds of lipoxygenase, the β-subunit of β-conglycinin, sucrose binding protein and Bowman-Birk protease inhibitor were negatively impacted by extreme heat stress in both genotypes, but these effects were less pronounced in the heat-tolerant genotype. Western blot analysis showed elevated accumulation of heat shock proteins (HSP70 and HSP17.6) in both lines in response to elevated temperatures during seed fill. Transmission electron microscopy showed that heat stress caused dramatic structural changes in the storage parenchyma cells. Extreme heat stress disrupted the structure and the membrane integrity of protein storage vacuoles, organelles that accumulate seed storage proteins. The detachment of the plasma membrane from the cell wall (plasmolysis) was commonly observed in the cells of the sensitive line. In contrast, these structural changes were less pronounced in the tolerant genotype, even under extreme heat stress, cells, for the most part, retained their structural integrity. The results of our study demonstrate the contrasting effects of heat stress on the seed protein composition and ultrastructural alterations that contribute to the tolerant genotype’s ability to tolerate high temperatures during seed development.