Heat-sensitive Cultivar Research Articles

Optimal sowing time to adapt soybean production to global warming with different cultivars in the Huanghuaihai Farming Region of China

ContextThe Huanghuaihuai Farming Region (HFR) is one of China’s largest soybean production zones, with climatic conditions in the HFR being near ideal. In recent decades, however, global warming has increasingly inhibited soybean production in this region. ObjectiveOur aim was to determine whether planting time and/or genetics (heat-resilient and heat-sensitive cultivars) enable adaptation of soybean cropping systems to the changing climate. MethodsTwo-year split-plot design field experiments comprising five different sowing dates and three cultivars (namely heat-resilient, heat-sensitive and widely grown ones) were conducted in the HFR in 2020 and 2021. ResultsDelayed sowing dates significantly elevated the average minimum temperature in the vegetative growth stage, fostering soybean growth and consequently truncating the vegetative growth stage. Later sowing reduced the occurrence of heat stress and minimized negative influences of heat stress on yield. Higher heat stress in the first two sowing treatments (1 June and 10 June) negatively influenced yields of Hedou14 (heat-sensitive cultivar) and Zhonghuang13 in 2020, while the highest yield was obtained for the third sowing treatment (20 June) for these two cultivars. In general, Jidou21 (heat-resilient cultivar) showed greater tolerance to increasing temperature, with higher yield at earlier sowing. Delayed sowing decreased temperature exposure and growing degree days (GDD), reducing the duration of grain filling, leaf area index and photosynthesis, in turn decreasing grain number per plant and 100-grain weight. Taken together, such factors inhibited yield of all cultivars in the year without heat stress. In contrast, high precipitation (2021) prolonged grain filling and increased yield. ConclusionsWe contend that optimizing sowing time is crucial for mitigating heat stress in heat-sensitive cultivars. We suggest that high yield is more likely to be realized when crops are exposed to GDD > 500℃·d and precipitation > 250 mm during grain filling. ImplicationsFuture studies aiming to elicit optimal sowing times for soybean should consider cultivar heat sensitivity relative to long term climatic conditions of the target agro-ecological region.

Physiological and Transcriptomic Responses of Bok Choy to Heat Stress.

High temperatures have adverse effects on the yield and quality of vegetables. Bok choy, a popular vegetable, shows varying resistance to heat. However, the mechanism underlying the thermotolerance of bok choy remains unclear. In this study, 26 bok choy varieties were identified in screening as being heat-resistant at the seedling stage; at 43 °C, it was possible to observe obvious heat damage in different bok choy varieties. The physiological and biochemical reactions of a heat-tolerant cultivar, Jinmei (J7), and a heat-sensitive cultivar, Sanyueman (S16), were analyzed in terms of the growth index, peroxide, and photosynthetic parameters. The results show that Jinmei has lower relative conductivity, lower peroxide content, and higher total antioxidant capacity after heat stress. We performed transcriptome analysis of the two bok choy varieties under heat stress and normal temperatures. Under heat stress, some key genes involved in sulfur metabolism, glutathione metabolism, and the ribosome pathway were found to be significantly upregulated in the heat-tolerant cultivar. The key genes of each pathway were screened according to their fold-change values. In terms of sulfur metabolism, genes related to protease activity were significantly upregulated. Glutathione synthetase (GSH2) in the glutathione metabolism pathway and the L3e, L23, and S19 genes in the ribosomal pathway were significantly upregulated in heat-stressed cultivars. These results suggest that the total antioxidant capacity and heat injury repair capacity are higher in Jinmei than in the heat-sensitive variety, which might be related to the specific upregulation of genes in certain metabolic pathways after heat stress.

Effectiveness of heat tolerance rice cultivars in preserving grain appearance quality under high temperatures in Japan – A meta-analysis

BackgroundClimate change, particularly rising temperatures, negatively affects rice grain quality, increasing chalky grain percentage (CG) and hampering rice grade and price. Heat-tolerant cultivars have been bred and released since the 2000 s, but the effectiveness of heat tolerance in reducing the occurrence of CG has yet to be quantified. ObjectivesThis study aimed to measure the effectiveness of breeding for better heat tolerance in reducing the negative impact of high temperatures on rice quality. MethodsThrough a systematic literature search, we developed a dataset including 1297 field observations covering 48 cultivars from five different heat tolerant ranks (HTRs) at 44 sites across Japan. A linear mixed-effect model (LME) and a random forest model (RF) were fitted to the data to analyze the effect of HTR and climatic factors such as the cumulative mean air temperature above 26 °C (TaHD), mean solar radiation, and mean relative humidity for 20 days after heading on CG. ResultsThe LME model explained 63% of the variation of the whole dataset with a 14% RMSE. The RF partial dependence plot revealed that the logit-transformed CG response to climate factors was linear, supporting the assumption of the LME. The statistical analysis showed that CG increased as a function of TaHD (P < 0.001), with significant differences among HTRs (P < 0.001). The strongest effect of TaHD was obtained for the lowest HTR and was found to decrease with increasing HTR. CG also increased with higher relative humidity (P < 0.001) and solar radiation (P < 0.01). Based on our modeling, we estimated that as TaHD increased from 20 to 80 °Cd (equivalent to a mean temperature increase from 27 °C to 30 °C), CG increased by 66% points (difference in CG) for cultivars with the lowest HTR, 45% points for cultivars with an intermediate HTR, and 19% points for cultivars with the highest HTR. Raising HTR by just one step (from intermediate to moderately tolerant) is projected to increase the proportion of first-grade rice at a grain-filling temperature of 27 °C, but tolerance levels need to be improved further in case of stronger warming. ConclusionsThe effect of high temperatures on CG was highly dependent on the cultivar’s HTR. Improvements in HTR effectively reduce the negative impacts of high temperatures on rice grain quality. SignificanceHeat-tolerant cultivars are projected to suppress the prevalence of CG more than threefold compared with heat-sensitive cultivars when grain-filling temperature increases from 27 to 30 °C.

Quantifying the Individual and Combined Effects of Short-Term Heat Stress at Booting and Flowering Stages on Nonstructural Carbohydrates Remobilization in Rice.

Rice production is threatened by climate change, particularly heat stress (HS). Nonstructural carbohydrates (NSCs) remobilization is a key physiological mechanism that allows rice plants to cope with HS. To investigate the impact of short-term HS on the remobilization of nonstructural carbohydrates (NSCs) in rice, two cultivars (Huaidao-5 and Wuyunjing-24) were subjected to varying temperature regimes: 32/22/27 °C as the control treatment, alongside 40/30/35 °C and 44/34/39 °C, for durations of 2 and 4 days during the booting, flowering, and combined stages (booting + flowering) within phytotrons across the years 2016 and 2017. The findings revealed that the stem's NSC concentration increased, while the panicle's NSCs concentration, the efficiency of NSCs translocation from the stem, and the stem NSC contribution to grain yield exhibited a consistent decline. Additionally, sugar and starch concentrations increased in leaves and stems during late grain filling and maturity stages, while in panicles, the starch concentration decreased and sugar concentration increased. The heat-tolerant cultivar, Wuyunjing-24, exhibited higher panicle NSC accumulation under HS than the heat-sensitive cultivar, Huaidao-5, which had more stem NSC accumulation. The flowering stage was the most vulnerable to HS, followed by the combined and booting stages. Heat degree days (HDDs) were utilized to quantify the effects of HS on NSC accumulation and translocation, revealing that the flowering stage was the most affected. These findings suggest that severe HS makes the stem the primary carbohydrate storage sink, and alleviation under combined HS aids in evaluating NSC accumulation, benefiting breeders in developing heat-tolerant rice varieties.

Exogenous application of melatonin mitigate the heat stress in different tomato (Solanum lycopersicum L.) cultivars

Heat stress alleviates yield and production of horticultural crops and is considered a major risk for sustainable agriculture. Melatonin acts as a first line soldier to regulate plant growth by creating a conducive environment under heat stress. Thus, the present study was performed in pots to mitigate the adverse impact of heat stress on four genotypes of tomato (two were heat sensitive and two were heat tolerant) through exogenous application of melatonin. The experiment was comprised of two treatments, control and foliar spray of melatonin @ 25 µM, under factorial design (CRD) with five replications by using heat-sensitive and heat-tolerant cultivars of tomato as a test crop. All the tomato varieties were treated with 25 µM melatonin through foliar spray and compared with control which remained untreated. All the growth and yield parameters and enzymatic activities of antioxidants including catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD) were increased significantly due to the application of melatonin. Moreover, the melatonin spray enhanced the osmolyte production such as malondialdehyde (MDA), proline contents, total soluble sugars, and fruit quality over control treatment. Concludingly, the heat-tolerant cultivars performed better under melatonin spray as compared to heat-sensitive cultivars of tomato.

Lipidomics-based insights into the physiological mechanism of wheat in response to heat stress

Lipids are the main components of plant cell biofilms and play a crucial role in plant growth, Understanding the modulation in lipid profiles under heat stress can contribute to understanding the heat tolerance mechanisms in wheat leaves. In the current study, two wheat cultivars with different heat tolerance levels were treated with optimum temperature (OT) and high temperature (HT) at the flowering stage, and the antioxidant enzyme activity in the leaves and the grain yield were determined. Further, lipidomics was studied to determine the changes in lipid composition in the leaves. The heat-tolerant cultivar ZM7698 exhibited higher antioxidant enzyme activity and lower malondialdehyde and H2O2 contents. High-temperature stress led to the remodeling of lipid profile in the two cultivars. The relative proportion of digalactosyl diacylglycerol (DGDG) and phosphatidylinositol (PI) components increased in the heat-tolerant cultivar under high-temperature stress, while it was decreased in the heat-sensitive cultivar. The lipid unsaturation levels of sulfoquinovosyl diacylglycerol (SQDG), monogalactosyl monoacylglycerol (MGMG), and phosphatidic acid (PA) decreased significantly in the heat-tolerant cultivar under high-temperature stress. The increase in unsaturation of monogalactosyl diacylglycerol (MGDG) and phosphatidylethanolamine (PE) in the heat-tolerant cultivar under high-temperature stress was lower than in the heat-sensitive cultivar. In addition, a high sitosterol/stigmasterol (SiE/StE) ratio was observed in heat-tolerant cultivar under high-temperature stress. Taken together, these results revealed that a heat-tolerant cultivar could enhance its ability to resist heat stress by modulating the composition and ratio of the lipid components and decreasing lipid unsaturation levels in wheat.

A mobile device to investigate the response of grapevine berries to heat stress

Reproducibly comparing the heat stress response of grapevine berries from different cultivars in the field is often limited by weather conditions during the growing season. This work presents a mobile heating device capable of controlled heat-stress induction on grapevine berries. The heater consisted of six 150 W infrared lamps mounted in a profile frame. The heating power of the lamps could be set individually by a control unit consisting of a single board computer and six temperature sensors positioned as desired. The heat energy applied to individual berries within a cluster decreases by the squared distance to the heat source, enabling the establishment of temperature profiles within individual clusters. Infrared thermography of the fruit surface and measurements conducted with a thermocouple inserted at the epidermis level showed comparable temperatures. Berries treated with high temperatures were sampled according to their visual appearance (i.e., sunburn symptoms). Only symptomatic berries showed a significant increase in electrolyte leakage, indicating cell damage. In a field experiment, the induction of sunburn necrosis symptoms with the presented device was used to predict a Lethal Dose (LD50) for sunburn necrosis symptoms of the Vitis vinifera L. cultivars Bacchus and Silvaner. The LD50 of Bacchus, known as a heat-sensitive cultivar, was about 3.2 °C lower than that of Silvaner. The presented device offers possibilities for a wide range of applications and the induction of precise temperature dynamics in the context of heat stress on fleshy fruit.

Transcriptome analysis of thermomorphogenesis in ovules and during early seed development in Brassica napus

BackgroundPlant sexual reproduction is highly sensitive to elevated ambient temperatures, impacting seed development and production. We previously phenotyped this effect on three rapeseed cultivars (DH12075, Topas DH4079, and Westar). This work describes the transcriptional response associated with the phenotypic changes induced by heat stress during early seed development in Brassica napus.ResultsWe compared the differential transcriptional response in unfertilized ovules and seeds bearing embryos at 8-cell and globular developmental stages of the three cultivars exposed to high temperatures. We identified that all tissues and cultivars shared a common transcriptional response with the upregulation of genes linked to heat stress, protein folding and binding to heat shock proteins, and the downregulation of cell metabolism. The comparative analysis identified an enrichment for a response to reactive oxygen species (ROS) in the heat-tolerant cultivar Topas, correlating with the phenotypic changes. The highest heat-induced transcriptional response in Topas seeds was detected for genes encoding various peroxidases, temperature-induced lipocalin (TIL1), or protein SAG21/LEA5. On the contrary, the transcriptional response in the two heat-sensitive cultivars, DH12075 and Westar, was characterized by heat-induced cellular damages with the upregulation of genes involved in the photosynthesis and plant hormone signaling pathways. Particularly, the TIFY/JAZ genes involved in jasmonate signaling were induced by stress, specifically in ovules of heat-sensitive cultivars. Using a weighted gene co-expression network analysis (WGCNA), we identified key modules and hub genes involved in the heat stress response in studied tissues of either heat-tolerant or sensitive cultivars.ConclusionsOur transcriptional analysis complements a previous phenotyping analysis by characterizing the growth response to elevated temperatures during early seed development and reveals the molecular mechanisms underlying the phenotypic response. The results demonstrated that response to ROS, seed photosynthesis, and hormonal regulation might be the critical factors for stress tolerance in oilseed rape.

Responses of Eight Differentially Heat Sensitive Tomato Cultivars against Chronic Ozone Exposure in the Indo-Gangetic Plain: Growth, Physiology, and Yield

Tropospheric ozone (O3) is an important abiotic stress to plants and its rising concentration adversely affects crop yield. The studies associated with differential responses of tomato (Solanum lycopersicum L.) cultivars to chronic elevated O3 are lacking and need to be further explored for the recognition of O3 resistant cultivars as an adaptive strategy. In the present research, differentially heat sensitive tomato cultivars were treated with elevated O3 (ambient + 20 ppb) to determine their responses by estimating the foliar injury symptoms, variations in growth, physiology, reproductive and yield related attributes. All the tomato cultivars exhibited foliar injury symptoms under elevated O3 treatment, and the intensity of injury corroborated with yield loss. Elevated O3 treatment negatively impacted biomass, growth, physiological and reproductive characteristics of all cultivars. The hierarchal cluster analysis, cumulative stress response index and yield indices differentiated cultivars into sensitive, moderately sensitive and O3 tolerant categories. The thermotolerant, VRT02 and Kashi chayan cultivars (O3 resistant) demonstrated lower yield losses, whereas the thermotolerant (O3 sensitive) Superbug exhibited higher foliar injury, greater alterations in physiology, growth and reproductive traits resulting in greater yield losses than other cultivars. The cultivars with different heat sensitivity did not respond similarly towards O3 stress. Cultivars VRT 02 and Kashi chayan can be recommended for cultivation in areas experiencing high O3 vis-à-vis high temperature conditions.

Responses of Aerial and Belowground Parts of Different Potato (Solanum tuberosum L.) Cultivars to Heat Stress

The mechanism of potato (Solanum tuberosum L.) thermotolerance has been the focus of intensive research for many years because plant growth and tuber yield are highly sensitive to heat stress. However, the linkage between the aerial and belowground parts of potato plants in response to high temperatures is not clear. To disentangle this issue, the aerial and belowground parts of the heat-resistant cultivar Dian187 (D187) and the heat-sensitive cultivar Qingshu 9 (Qs9) were independently exposed to high-temperature (30 °C) conditions using a special incubator. The results indicated that when the belowground plant parts were maintained at a normal temperature, the growth of the aerial plant parts was maintained even when independently exposed to heat stress. In contrast, the treatment that independently exposed the belowground plant parts to heat stress promoted premature senescence in the plant's leaves, even when the aerial plant parts were maintained at a normal temperature. When the aerial part of the plant was independently treated with heat stress, tuberization belowground was not delayed, and tuberization suppression was not as severe as when the belowground plant parts independently underwent heat stress. Heat stress on the belowground plant parts alone had virtually no damaging effects on the leaf photosynthetic system but caused distinct tuber deformation, secondary growth, and the loss of tuber skin colour. Transcriptome analysis revealed that the treatment of the belowground plant parts at 30 °C induced 3361 differentially expressed genes in the Qs9 cultivar's expanding tubers, while the D187 cultivar had only 10,148 differentially expressed genes. Conversely, when only the aerial plant parts were treated at 30 °C, there were just 807 DEGs (differentially expressed genes) in the D187 cultivar's expanding tubers compared with 6563 DEGs in the Qs9 cultivar, indicating that the two cultivars with different heat sensitivities have distinct regulatory mechanisms of tuberization when exposed to heat stress. The information provided in this study may be useful for further exploring the genes associated with high-temperature resistance in potato cultivars.

Strategies for indica rice adapted to high-temperature stress in the middle and lower reaches of the Yangtze River.

High temperatures caused by climate warming severely affect the grain yield and quality of rice. In this study, the rice cultivars Longliangyou Huazhan (LLYHZ) and Quanliangyou 2118 (QLY2118) were selected as the experimental materials for investigation of an optimal cultivation system under high-temperature treatment. In addition, the heat-resistant cultivar Huanghuazhan (HHZ) and heat-sensitive cultivar Huiliangyou 858 (HLY858) were chosen as the experimental materials to study the effects of exogenous plant growth regulators on heat stress responses under high-temperature treatment. The results showed that mechanical transplanting of carpet seedlings and delayed sowing effectively increased the leaf area index and reduced the canopy temperature of LLYHZ and QLY2118. Furthermore, carpet seedling mechanical transplantation and delayed sowing improved grain yield and quality. Spray application of five plant growth regulators revealed that brassinolide and salicylic acid had the strongest effects on significantly improving antioxidant enzyme activities in the panicle, which would reduce the damage caused by the accumulation of reactive oxygen species and enhance plant tolerance of high-temperature stress. In addition, brassinolide and salicylic acid enhanced the percentage of anther dehiscence and percentage seed set. In this study, a set of simplified eco-friendly cultivation techniques for single-season indica rice adaptation to high-temperature stress was established. These results will be of great importance in alleviating the effects of high-temperature stress on rice production.

Transcriptome analysis reveals chrysanthemum flower discoloration under high-temperature stress.

Temperature is an important environmental factor affecting plant anthocyanin synthesis. High temperatures are associated with decreased anthocyanin pigmentation in chrysanthemum. To reveal the effects of high temperature on anthocyanin biosynthesis in chrysanthemum, ray florets of the heat-sensitive cultivar “Nannong Ziyunying” (ZYY) were subjected to RNA sequencing. A total of 18,286 unigenes were differentially expressed between the control and treatment groups. Functional annotation and enrichment analyses of these unigenes revealed that the heat shock response and flavonoid pathways were significantly enriched, suggesting that the expression of these genes in response to high temperature is associated with the fading of chrysanthemum flower color. In addition, genes related to anthocyanin synthesis and heat shock response were differentially expressed under high-temperature stress. Finally, to further investigate the molecular mechanism of discoloration under high-temperature stress and facilitate the use of marker-assisted breeding for developing novel heat-tolerant cultivars, these results were used to mine candidate genes by analyzing changes in their transcription levels in chrysanthemum.

Impact of summer heat stress inducing physiological and biochemical responses in herbaceous peony cultivars (Paeonia lactiflora Pall.) from different latitudes

As global temperatures continue to rise, heat stress and its severity are projected to advance as a major abiotic stress, seriously limiting the growth and production of herbaceous peony (Paeonia lactiflora Pall.), especially in low-latitude areas. Therefore, determining the ravaging effects of heat stress on the growth and development of herbaceous peony has become a prerequisite for expanding the cultivation area of this world-renowned ornamental crop. Comprehensive research on physiological and biochemical responses to summer heat stress was conducted between low-latitude and midlatitude herbaceous peony cultivars at low latitudes. Field observations showed that the stay-green (SG) duration varied among the cultivars from different latitudes and had a direct correlation with the level of heat damage. As the heat stress intensified, chlorophyll (Chl) contents and Chl fluorescence were decreased in the six cultivars. On the contrary, the relative electrical conductivity (REC) increased sharply, with the low-latitude ‘Hang Baishao’ presenting the lowest REC among the six cultivars before August 15 (with the highest temperatures). Photosynthetic curves showed more sustained photosynthesis in ‘Hang Baishao’, ‘Meiju’ and ‘Bo Baishao’. Based on principal component analysis (PCA) and subordinate function value analysis, ‘Hang Baishao’ was deduced as the most heat-tolerant cultivar, whereas ‘Zhuguang’ as a most heat-sensitive cultivar out of the six cultivars. The oxidative stress analysis between the two cultivars indicated an over-accumulation of reactive oxygen species (ROS) and malondialdehyde (MDA) with lower antioxidant enzyme activity in ‘Zhuguang’ than ‘Hang Baishao’. The results imply that heat-tolerant ‘Hang Baisao’ exhibited minimal heat damage and a delayed SG duration based on its enhanced antioxidant enzyme activity and heat acclimation under high-temperature stress. This study could provide insights into the responses and adaptions of peonies to heat stress and aid in the breeding of excellent peonies with improved heat resistance under ever-changing climatic conditions.

Heat Stress during Meiosis Has Lasting Impacts on Plant Growth and Reproduction in Wheat (Triticum aestivum L.)

Meiosis is the least explored stage for thermotolerance in wheat. We evaluated the impact of 5 d of moderate transient daily heat stress during meiosis in the main stem spike on physiological and grain yield traits in 30 diverse wheat cultivars which vary widely in heat tolerance and sensitivity. We found that a moderate heat stress event during meiosis in the main stem spike had lasting impacts on plant growth and reproduction in heat-sensitive, but not heat-tolerant, wheat cultivars. Heat-tolerant cultivars maintained grain yield, grain number and individual grain weight in the main stem spike and also total plant grain yield and biomass in the heat stress treatment relative to the control. Heat-sensitive cultivars responded to heat stress by producing fewer and smaller grains per spikelet on the main stem, fewer tillers, lower biomass and lower total plant grain yield in the high temperature treatment relative to the control. Heat-sensitive cultivars produced higher flag leaf chlorophyll content in the high temperature treatment relative to the control than heat-tolerant cultivars during the first 3 d of heat treatment. There was small reduction in pollen viability from 98% to 96% following heat stress during meiosis which was unrelated to heat tolerance or sensitivity. Moderate transient heat stress during meiosis did not greatly reduce the production of viable male gametes, but had long-lasting negative impacts on fertilization and subsequent seed production in heat-sensitive cultivars.

Evaluation of some bread wheat genotypes for heat tolerance under terminal heat stress conditions

Terminal heat stress leads to significant yield reduction in wheat. Thus, the determination of heat tolerant genotypes is of major importance in wheat breeding program. The present study was conducted at Shandaweel agricultural research station, Sohag, Egypt during 2019/2020 and 2020/2021 growing seasons, to evaluate twelve bread wheat genotypes under normal sowing (20 November) and late sowing (30 December) dates, the experiment set up as a randomized complete block design with three replications. Results revealed that late sowing (terminal heat stress) had a significant adverse impact on agronomic, physiological traits and grain carbohydrate content. The genotype Shandaweel 2, followed by Giza 171 and Sids 14 performed better than other genotypes for grain yield under the normal sowing. On the other side, Shandaweel 2 outperformed the tested genotypes under the late sowing. Based on heat susceptibility index (HSI), the cultivars Sids 12, Misr 2, Sakha 95 and genotype Shandaweel 2 showed HSI<1 and they can be labeled as heat tolerant genotypes, while Sids 14, Misr 1, Giza 171 and Misr 3 showed HSI>1 and they can be considered as heat sensitive cultivars. GGE biplot analysis and ranking of genotypes revealed that the new line Shandaweel 2 was the an ideal genotype in terms of yielding ability and stability and it was suitable for planting under normal and late sowing conditions, while Giza 171 was suitable for planting under the normal sowing. The GYT biplot and superiority index showed that Shandaweel 2 and Giza 171 had the best traits profile.

Heat-tolerant pepper cultivar exhibits high rates of chlorophyll, photosynthesis, stomatal conductance and transpiration in heat stress regime at fruit developing stage

Relevance. Abiotic stress, as heat, significantly affect plant and floral organs growth and development, fruit set, productivity, the quality, and survival of crops. Heat injury occurs when plants are exposed to these temperatures for a long period of time. Depending on the intensity and duration of exposure to the high temperatures, photosynthesis, respiration, membrane integrity, water relations and the hormone balance of the plants may affected.Material and methods. In this study used the commercial pepper cultivar “NW Bigarim” (HT37) released in South Korea and accessions “Kobra” (HT1) and “Samchukjaere” (HT7) selected as heat tolerant and susceptible, respectively. Total chlorophyll index and photosynthetic activities measured using a SPAD meter (Konica, Japan) and portable photosynthesis measurement system (LI-6400, LI-COR Bioscience, Lincoln, NE, USA), respectively.Results. To evaluate the positive effects of high temperature regime (40/28°C day/night, 14/10-h light/dark cycle) on the response of photosynthetic parameters in pepper plants with different heat susceptibility, we measured the total chlorophyll content (CHL) and photosynthetic activities such as photosynthesis (Pn), stomatal conductance to H2O (Gs) and transpiration rate (Tr) in a heat-tolerant (HT1) and -susceptible cultivars (HT7) in comparison with released cultivar (HT37) at fruit development stage. Heat-tolerant cultivars showed higher and more stable index of the CHL, Pn, Gs and Tr than those in heat-sensitive cultivars for 14 days of heat treatment (HT) period. However, the initial index of Pn, Gs and Tr showed significant alteration among pepper plants regardless of thermotolerance rate before HT on day 0 and day 7 after recovery at normal treatment condition (NT) except for CHL, meaning that plants response to high temperature regime is different from that in normal condition. These results suggest that constant high rates of Pn, Gs and Tr as well as of CHL in heat stress condition periods confer to avoid from heat injury during reproductive growth stages.

Nanopore-Based Comparative Transcriptome Analysis Reveals the Potential Mechanism of High-Temperature Tolerance in Cotton (Gossypium hirsutum L.).

Extreme high temperatures are threatening cotton production around the world due to the intensification of global warming. To cope with high-temperature stress, heat-tolerant cotton cultivars have been bred, but the heat-tolerant mechanism remains unclear. This study selected heat-tolerant (‘Xinluzao36′) and heat-sensitive (‘Che61-72′) cultivars of cotton treated with high-temperature stress as plant materials and performed comparative nanopore sequencing transcriptome analysis to reveal the potential heat-tolerant mechanism of cotton. Results showed that 120,605 nonredundant sequences were generated from the raw reads, and 78,601 genes were annotated. Differentially expressed gene (DEG) analysis showed that a total of 19,600 DEGs were screened; the DEGs involved in the ribosome, heat shock proteins, auxin and ethylene signaling transduction, and photosynthesis pathways may be attributed to the heat tolerance of the heat-tolerant cotton cultivar. This study also predicted a total of 5118 long non-coding RNAs (lncRNAs)and 24,462 corresponding target genes. Analysis of the target genes revealed that the expression of some ribosomal, heat shock, auxin and ethylene signaling transduction-related and photosynthetic proteins may be regulated by lncRNAs and further participate in the heat tolerance of cotton. This study deepens our understandings of the heat tolerance of cotton.

High temperatures disturb ovule development in field pea (Pisum sativum)

High temperatures affect reproductive growth and lead to yield loss in many crops. Field pea is heat sensitive, but little is known about the effect of high temperatures on field pea ovules. We investigated the impact of heat on ovules of flowers at various reproductive nodes of field pea using growth chambers. We exposed 6 cultivars exhibiting diverse heat tolerance to 4 days of heat (35 °C day/18 °C night) during early flowering. Post-treatment ovules and embryo sacs were assessed using clearing by light microscopy and fluorescence microscopy. Results indicated that greater ovule and embryo sac development occurred on some nodes, but poor ovule and embryo sac expansion resulted on other nodes of the same heat-treated plants. Whereas advanced ovule and embryo sac development were identified on heat-tolerant cultivars, a combination of advanced and less advanced ovule and embryo sac development occurred in intermediate and heat-sensitive cultivars. More than 90% of the affected ovules displayed embryos at various stages of development, which indicated disruption around fertilization or shortly thereafter. Callose accumulation around the vascular bundle within ovules suggested disruption of assimilate transport to the embryo sac. The contrasting pattern of ovule development at different nodes implied a conflict between early aging and maternal supply of heat-treated plants.

Unravelling the Role of Temperature and Photoperiod on Poinsettia Heat Delay

The effects of day temperature (DT), night temperature (NT), and night length (NL) were evaluated on the flowering responses of heat-tolerant and heat-sensitive poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) cultivars Orion Red and Prestige Red, respectively. Plants were placed under 60 DT × NT × NL treatments that consisted of three DT (20, 24, 28 °C), four NT (16, 20, 24, 28 °C), and five NL (10, 11, 12, 13, 14 hours) for the first 17 days of the experiment. After 17 days, all plants were consolidated to one greenhouse with an inductive environment (14-hour NL, 24 ± 2.0 °C DT and 21.2 ± 1.4 °C NT), and the timing of first color, visible bud, and anthesis were recorded. ‘Orion Red’ reached anthesis 8 to 10 days faster than ‘Prestige Red’ across all NLs; however, in both cultivars, days to anthesis decreased in a sigmoidal pattern as NL increased. The relative rate of progress to anthesis (1/days to anthesis) under a 12-hour NL was approximately half that of plants grown at a 13- or 14-hour NL. At a 12-hour NL, the relative rate of progress to anthesis decreased linearly as DT increased for both cultivars. At 13- to 14-hour NL, DT had relatively little effect on the relative rate of progress to anthesis. Thus, high DT delayed flowering of both heat-tolerant and heat-sensitive cultivars when flower initiation occurred under NL, typical of naturally occurring NLs in September and early October (i.e., 12-hour NL), whereas high DT did not delay flowering for either cultivar under a 14-hour NL, which is typically provided under black cloth systems. In contrast, the flowering responses to NT were quite different for the two cultivars. The heat-tolerant cultivar showed relatively little change in the relative rate of progress to anthesis as NT increased from 16 to 28 °C within each NL treatment; however, the heat-sensitive cultivar displayed a large decrease in the relative rate progress to anthesis as NT increased from 20 to 28 °C within each NL treatment. Although the delayed flowering that occurred at 28 °C and 14-hour NL was significant, the relative rate of progress to anthesis at this treatment was significantly higher than the 28 °C and 12-hour NL treatment. This suggests that artificially shortening NL to 14 hours with a black cloth system does not prevent heat delay of poinsettia, but it allows for more rapid flowering than if flower initiation took place under natural NL (≈12 hours). To summarize, high DT affected flowering when flower initiation took place at 12-hour NL for heat-tolerant and heat-sensitive poinsettia cultivars, whereas high NT uniquely delayed flowering of the heat-sensitive cultivar at NL from 12 to 14 hours.

Inheritance of heat tolerance in perennial ryegrass (Lolium perenne, Poaceae): evidence from progeny array analysis.

BackgroundHeat stress is considered one of the most important environmental factors influencing plant physiology, growth, development, and reproductive output. The occurrence and damage caused by heat stress will likely increase with global climate change. Thus, there is an urgent need to better understand the genetic basis of heat tolerance, especially in cool season plants.Materials and MethodsIn this study, we assessed the inheritance of heat tolerance in perennial ryegrass (Lolium perenne L. subspecies perenne) , a cool season grass, through a comparison of two parental cultivars with their offspring. We crossed plants of a heat tolerant cultivar (Kangaroo Valley) with plants of a heat sensitive cultivar (Norlea), to generate 72 F1 hybrid progeny arrays. Both parents and their progeny were then exposed to heat stress for 40 days, and their photosynthetic performance (Fv/Fm values) and leaf H2O2 content were measured.ResultsAs expected, Kangaroo Valley had significantly higher Fv/Fm values and significantly lower H2O2 concentrations than Norlea. For the F1 progeny arrays, values of Fv/Fm decreased gradually with increasing exposure to heat stress, while the content of H2O 2 increased. The progeny had a wide distribution of Fv/Fm and H 2O2 values at 40 days of heat stress. Approximately 95% of the 72 F1 progeny arrays had Fv/Fm values that were equal to or intermediate to the values of the two parental cultivars and 68% of the progeny arrays had H2O2 concentrations equal to or intermediate to their two parents.ConclusionResults of this study indicate considerable additive genetic variation for heat tolerance among the 72 progeny arrays generated from these crosses, and such diversity can be used to improve heat tolerance in perennial ryegrass cultivars. Our findings point to the benefits of combining physiological measurements within a genetic framework to assess the inheritance of heat tolerance, a complex plant response.