Impedance Flow Cytometry for Selection of Pollen Traits Under High Temperature Stress in Pepper

High temperature stress is a major limiting factor for pepper productivity, which will continue to be a problem under climate change scenarios. Developing heat tolerant cultivars is critical for sustained pepper production, especially in tropical and subtropical regions. In fruiting crops, like pepper, reproductive tissues, especially pollen, are the most sensitive to high temperature stress. Typically, pollen viability and germination are assessed through staining and microscopy, which is tedious and potentially inaccurate. To increase efficiency in assessing pollen traits of pepper, the use of impedance flow cytometry (IFC) has been proposed. We conducted three independent experiments to determine the most effective methodology to use IFC for evaluating pollen traits for heat tolerance in pepper. Seven floral developmental stages were evaluated, and stages 3, 4, and 5 were found to best combine high pollen concentration and activity. Flowers in development stages 3, 4, or 5 were then heat treated at 41, 44, 47, 50, and 55 °C or not heat treated (control). The critical temperature to assess heat tolerance using IFC was found to be 50 °C, with a reduction in pollen activity and concentration occurring at temperatures greater than 47 °C. Twenty-one entries of pepper were then accessed for pollen traits using the staining and IFC methods over 2 months, April (cooler) and June (hotter). Growing environment was found to be the greatest contributor to variability for nearly all pollen traits assessed, with performance during June nearly always being lower. PBC 507 and PBC 831 were identified as being new sources of heat tolerance, based on using IFC for assessing pollen. Pollen viability determined by staining and pollen activity determined using IFC were significantly positively correlated, indicating that IFC is an efficient and accurate method to assess pollen traits in pepper. This work provides a basis for further research in this area and supports more efficient breeding of heat-tolerant cultivars.

Unraveling Heat Tolerance in Upland Cotton (Gossypium hirsutum L.) Using Univariate and Multivariate Analysis

The ever-changing global environment currently includes an increasing ambient temperature that can be a devastating stress for organisms. Plants, being sessile, are adversely affected by heat stress in their physiology, development, growth, and ultimately yield. Since little is known about the response of biochemical traits to high-temperature ambiance, we evaluated eight parental lines (five lines and three testers) and their 15 F1 hybrids under normal and high-temperature stress to assess the impact of these conditions over 2 consecutive years. The research was performed under a triplicate randomized complete block design including a split-plot arrangement. Data were recorded for agronomic, biochemical, and fiber quality traits. Mean values of agronomic traits were significantly reduced under heat stress conditions, while hydrogen peroxide, peroxidase, total soluble protein, superoxide dismutase, catalase (CAT), carotenoids, and fiber strength displayed higher mean values under heat stress conditions. Under both conditions, high genetic advance and high heritability were observed for seed cotton yield (SCY), CAT, micronaire value, plant height, and chlorophyll-a and b content, indicating that an additive type of gene action controls these traits under both the conditions. For more insights into variation, Pearson correlation analysis and principal component analysis (PCA) were performed. Significant positive associations were observed among agronomic, biochemical, and fiber quality-related traits. The multivariate analyses involving hierarchical clustering and PCA classified the 23 experimental genotypes into four groups under normal and high-temperature stress conditions. Under both conditions, the F1 hybrid genotype FB-SHAHEEN × JSQ WHITE GOLD followed by Ghuari-1, CCRI-24, Eagle-2 × FB-Falcon, Ghuari-1 × JSQ White Gold, and Eagle-2 exhibited better performance in response to high-temperature stress regarding the agronomic and fiber quality-related traits. The mentioned genotypes could be utilized in future cotton breeding programs to enhance heat tolerance and improve cotton yield and productivity through resistance to environmental stressors.

Antibiotics Alter Pocillopora Coral-Symbiodiniaceae-Bacteria Interactions and Cause Microbial Dysbiosis During Heat Stress

Symbioses between eukaryotes and their associated microbial communities are fundamental processes that affect organisms’ ecology and evolution. A unique example of this is reef-building corals that maintain symbiotic associations with dinoflagellate algae (Symbiodiniaceae) and bacteria that affect coral health through various mechanisms. However, little is understood about how coral-associated bacteria communities affect holobiont heat tolerance. In this study, we investigated these interactions in four Pocillopora coral colonies belonging to three cryptic species by subjecting fragments to treatments with antibiotics intended to suppress the normal bacteria community, followed by acute heat stress. Separate treatments with only antibiotics or heat stress were conducted to compare the effects of individual stressors on holobiont transcriptome responses and microbiome shifts. Across all Pocillopora species examined, combined antibiotics and heat stress treatment significantly altered coral-associated bacteria communities and caused major changes in both coral and Cladocopium algal symbiont gene expression. Individually, heat stress impaired Pocillopora protein translation and activated DNA repair processes, while antibiotics treatments caused downregulation of Pocillopora amino acid and inorganic ion transport and metabolism genes and Cladocopium photosynthesis genes. Combined antibiotics-heat stress treatments caused synergistic effects on Pocillopora and Cladocopium gene expression including enhanced expression of oxidative stress response genes, programed cell death pathways and proteolytic enzymes that indicate an exacerbated response to heat stress following bacteria community suppression. Collectively, these results provide further evidence that corals and their Symbiodiniaceae and bacteria communities engage in highly coordinated metabolic interactions that are crucial for coral holobiont health, homeostasis, and heat tolerance.

Diverse Heat Tolerance of the Yeast Symbionts of Platycerus Stag Beetles in Japan

The genus Platycerus (Coleoptera: Lucanidae) is a small stag beetle group, which is adapted to cool-temperate deciduous broad-leaved forests in East Asia. Ten Platycerus species in Japan form a monophyletic clade endemic to Japan and inhabit species-specific climatic zones. They are reported to have co-evolutionary associations with their yeast symbionts of the genus Sheffersomyces based on host cytochrome oxidase subunit I (COI) and yeast intergenic spacer (IGS) phylogenies. Here we examined the heat tolerances of the yeast colonies isolated from the mycangia of 37 females belonging ten Japanese Platycerus species. The upper limits of growth and survival temperatures of each colony were decided by cultivating it at ten temperature levels between 17.5 and 40°C. Although both temperatures varied during 25.0–31.25°C, the maximum survival temperatures (MSTs) were a little higher than the maximum growth temperatures (MGTs) in 16 colonies. Pearson’s correlations between these temperatures and environmental factors (elevation and 19 bioclimatic variables from Worldclim database) of host beetle collection sites were calculated. These temperatures were significantly correlated with elevation negatively, the maximum temperature of the warmest month (Bio5) positively, and some precipitative variables, especially in the warm season (Bio12, 13, 16, 18) negatively. Sympatric Platycerus kawadai and Platycerus albisomni share the same lineage of yeast symbionts that exhibit the same heat tolerance, but the elevational lower range limit of P. kawadai is higher than that of P. albisomni. Based on the field survey in their sympatric site, the maximum temperature of host wood of P. kawadai larvae is higher about 2–3°C than that of P. albisomni larvae in the summer, which may restrict the elevational range of P. kawadai to higher area. In conclusion, it is suggested that the heat tolerance of yeast symbionts restricts the habitat range of their host Platycerus species or/and that the environmental condition that host Platycerus species prefers affect the heat tolerance of its yeast symbionts.

Nanoparticles in Agriculture: Characterization, Uptake and Role in Mitigating Heat Stress

Abiotic stresses like heat, drought, and salinity are among the major threats to sustainable crop production. These stresses induce numerous adverse effects in plants by impairing biochemical, physiological and molecular processes, eventually affecting plant growth, development and productivity. The rising temperature is one of the major causes of heat stress in agriculture. The variation in temperature during crop development has led to devastating agricultural losses in terms of yield. To adapt and mitigate these effects, germplasm scientists and agronomists aim to develop heat-tolerant varieties or cultivars. These efforts generally include the identification of alleles responsible for heat tolerance and their introgression into breeding populations through conventional or biotechnological methods. However, heat tolerance is a very complex physio-biochemical response of plants governed by a number of genes positioned at different loci. The accumulation of various additive gene effects into a single genotype is an extremely tedious and time-consuming process in both plant breeding and biotechnology. Recent advancements in agricultural nanotechnology have raised expectations for sustainable productivity without altering the genetic make-up of plants. In this milieu, the application of biologically active nanoparticles (NPs) could be a novel approach to enhance heat tolerance in crops. Recently, the NPs from silver, silicon, titanium and selenium have been proven valuable for plants to combat heat stress by altering their physiological and biochemical responses. Due to nano-scale size and the high surface area along with their slow and steady release, the NPs exert positive effects in plants through their growth-promoting and antioxidant capabilities. In this review, various technologies used for NPs characterization and their applications in agriculture have been discussed. The review further elaborates the uptake mechanism of NPs and their translocation in different plant parts along with the factors affecting them. This article also describes the role of metal or metal oxide NPs, as well as nano, encapsulated plant growth regulators and signal molecules in heat stress tolerance. The review will provide an insight to the scientists working in the area of agricultural sciences to explore new NPs to encounter different types of biotic and abiotic stresses.

Identification of QTLs affecting post-anthesis heat stress responses in European bread wheat

Key message The response of a large panel of European elite wheat varieties to post-anthesis heat stress is influenced by 17 QTL linked to grain weight or the stay-green phenotype. Abstract Heat stress is a critical abiotic stress for winter bread wheat (Triticum aestivum L.) especially at the flowering and grain filling stages, limiting its growth and productivity in Europe and elsewhere. The breeding of new high-yield and stress-tolerant wheat varieties requires improved understanding of the physiological and genetic bases of heat tolerance. To identify genomic areas associated with plant and grain characteristics under heat stress, a panel of elite European wheat varieties (N = 199) was evaluated under controlled conditions in 2016 and 2017. A split-plot design was used to test the effects of high temperature for ten days after flowering. Flowering time, leaf chlorophyll content, the number of productive spikes, grain number, grain weight and grain size were measured, and the senescence process was modeled. Using genotyping data from a 280 K SNP chip, a genome-wide association study was carried out to test the main effect of each SNP and the effect of SNP × treatment interaction. Genotype × treatment interactions were mainly observed for grain traits measured on the main shoots and tillers. We identified 10 QTLs associated with the main effect of at least one trait and seven QTLs associated with the response to post-anthesis heat stress. Of these, two main QTLs associated with the heat tolerance of thousand-kernel weight were identified on chromosomes 4B and 6B. These QTLs will be useful for breeders to improve grain yield in environments where terminal heat stress is likely to occur.

Sitosterol-mediated Antioxidant Regulation to Enhance Heat Tolerance in Creeping Bentgrass

Heat stress symptoms in cool-season plants are characterized by loss of chlorophyll (Chl) and membrane stability, as well as oxidative damage. The objectives of this study were to determine whether foliar application of β-sitosterol, a naturally occurring plant metabolite, may promote heat tolerance by suppressing heat-induced leaf senescence as indicated by the maintenance of healthy turf quality (TQ), and Chl and membrane stability; and to determine its roles in regulating antioxidant metabolism in creeping bentgrass (Agrostis stolonifera). ‘Penncross’ plants were exposed to heat stress (35/30 °C day/night) optimal temperature conditions (nonstressed control, 22/17 °C day/night) for a duration of 28 days in environment-controlled growth chambers. Plants were foliar-treated with β-sitosterol (400 µM) or water only (untreated control) before heat stress, and at 7-day intervals through 28 days of heat stress. Plants treated with β-sitosterol had significantly greater TQ and Chl content, and significantly less electrolyte leakage (EL) than untreated controls at 21 and 28 days of heat stress. Application of β-sitosterol reduced malondialdehyde (MDA) content significantly at 21 and 28 days of heat stress, and promoted the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) from 14 through 28 days of heat stress. β-Sitosterol effectively improved heat tolerance through suppression of leaf senescence in creeping bentgrass exposed to heat stress in association with the alleviation of membrane lipid peroxidation and activation of the enzymatic antioxidant system.

Efficient Evaporative Cooling and Pronounced Heat Tolerance in an Eagle-Owl, a Thick-Knee and a Sandgrouse

Avian evaporative cooling and the maintenance of body temperature (Tb) below lethal limits during heat exposure has received more attention in small species compared to larger-bodied taxa. Here, we examined thermoregulation at air temperatures (Tair) approaching and exceeding normothermic Tb in three larger birds that use gular flutter, thought to provide the basis for pronounced evaporative cooling capacity and heat tolerance. We quantified Tb, evaporative water loss (EWL) and resting metabolic rate (RMR) in the ∼170-g Namaqua sandgrouse (Pterocles namaqua), ∼430-g spotted thick-knee (Burhinus capensis) and ∼670-g spotted eagle-owl (Bubo africanus), using flow-through respirometry and a stepped Tair profile with very low chamber humidities. All three species tolerated Tair of 56–60°C before the onset of severe hyperthermia, with maximum Tb of 43.2°C, 44.3°C, and 44.2°C in sandgrouse, thick-knees and eagle-owls, respectively. Evaporative scope (i.e., maximum EWL/minimum thermoneutral EWL) was 7.4 in sandgrouse, 12.9 in thick-knees and 7.8 in eagle-owls. The relationship between RMR and Tair varied substantially among species: whereas thick-knees and eagle-owls showed clear upper critical limits of thermoneutrality above which RMR increased rapidly and linearly, sandgrouse did not. Maximum evaporative heat loss/metabolic heat production ranged from 2.8 (eagle-owls) to 5.5 (sandgrouse), the latter the highest avian value yet reported. Our data reveal some larger species with gular flutter possess pronounced evaporative cooling capacity and heat tolerance and, when taken together with published data, show thermoregulatory performance varies widely among species larger than 250 g. Our data for Namaqua sandgrouse reveal unexpectedly pronounced variation in the metabolic costs of evaporative cooling within the genus Pterocles.