High Night Temperature Research Articles

Analysis of CsPAP-fib regulation of cucumber female differentiation in response to low night temperature conditions

Abstract In this study, the expression pattern of CsPAP-fib under different night temperature conditions (12 °C, 18 °C, and 24 °C) was analyzed using qRT-PCR, the subcellular localization of CsPAP-fib protein was determined, and sense and antisense CsPAP-fib were transformed into cucumber. The first node with female flowers and the female flower rate were calculated and recorded. Next, the ethylene and gibberellin contents were determined. The expression of CsPAP-fib in cucumber leaves was the highest under the low night temperature (12 °C) condition and was significantly higher than that in the roots, stems and shoot tips; however, under the high night temperature (24 °C) and normal night temperature (18 °C) conditions, no significant differences in CsPAP-fib expression in the roots, stems, leaves, shoot tips and other organs were observed. The expression of CsPAP-fib was the highest in cucumber leaves during the two-leaf stage and was significantly higher than that during the four-leaf stage. CsPAP-fib played a functional role mainly in chloroplasts. The overexpression of CsPAP-fib significantly improved the rate of cucumber female flowering and reduced the first node with a female flower. Thus, CsPAP-fib is a relevant gene for the regulation of cucumber female differentiation under low night temperature conditions. Altogether, CsPAP-fib is induced by a low night temperature (12 °C) and promotes the formation of cucumber femaleness by increasing the female flowering rate and decreasing the first node with a female flower. CsPAP-fib may be a relevant gene for cucumber femaleness differentiation at a low night temperature.

Effect of high night temperature on storage lipids and transcriptome changes in developing seeds of oilseed rape.

Global warming causes a faster increase of night temperature than of day temperature in tropical and subtropical zones. Little is known about the effect of high night temperature on storage lipids and transcriptome changes in oilseed rape. This study compared the total fatty acids and fatty acid compositions in seeds of two oilseed rape cultivars between high and low night temperatures. Their transcriptome profiles were also analyzed. High night temperature significantly affected the total fatty acids and fatty acid compositions in seeds of both low and high oil content cultivars, namely Jiuer-13 and Zheyou-50, thereby resulting in 18.9% and 13.7% total fatty acid reductions, respectively. In particular, high night temperature decreased the relative proportions of C18:0 and C18:1 but increased the proportions of C18:2 and C18:3 in both cultivars. In-depth analysis of transcriptome profiles revealed that high night temperature up-regulated gibberellin signaling during the night-time. This up-regulation was associated with the active expression of genes involved in fatty acid catabolism, such as those in β-oxidation and glyoxylate metabolism pathways. Although the effect of temperature on plant lipids has been previously examined, the present study is the first to focus on night temperature and its effect on the fatty acid composition in seeds.

Transcriptome profiling reveals candidate genes associated with sex differentiation induced by night temperature in cucumber

Abstract The sex differentiation of cucumber directly affects cucumber fruit yield, and low night temperature (LT) promotes female flower differentiation. However, studies on the effects of LT on sex differentiation are scarce. To better understand this mechanism, we used transcriptomics to examine the expression patterns of genes related to female flower differentiation in the cucumber cultivar ‘C09-123’ under LT and high night temperature (HT). We identified a total of 1654 differentially expressed genes in response to LT. There were 1147 up-regulated genes and 507 down-regulated genes under LT compared with their expression under HT. Gene ontology (GO) analysis revealed that the differentially expressed genes were mainly involved in cellular process, metabolic process, response to stimulus process and other processes (biological process). Many of these differentially expressed genes (DEGs) were related to glucose metabolism, cysteine and methionine metabolism and the ethylene and auxin signal transduction pathway and were up-regulated under LT, which promotes female differentiation, compared with their expression level under HT. These results suggest that changes in these genes are likely to affect the corresponding metabolism, thus inducing the female flower differentiation of cucumber under LT. Ethylene and auxin play important roles in the induction of female flower differentiation under LT. This study provides valuable resources for further exploring the molecular basis of LT induction of female flower differentiation and for enabling targeted breeding strategies for developing varieties with superior strong female differentiation to achieve yield potential.

Non-Structural Carbohydrates Accumulation in Contrasting Rice Genotypes Subjected to High Night Temperatures

Non-structural carbohydrates (NSC) accumulation and photosynthesis traits were studied in two rice (Oryza sativa L.) genotypes maintained under control (22/30 °C - night/day) and at high night temperatures (HNT) (28/30 °C) conditions from heading to milk stage. Rice cultivars were Nagina22 - N22 and BRS Querência - Quer, which are tolerant and sensitive to high temperatures, respectively. The source-sink flow related attributes were tested to understand the nature of NSC accumulation and translocation. Compared to N22, Quer maintained higher stem starch in glucose on seventh day after heading and at milk stage independently of imposed temperatures. However, the levels of starch in glucose were lower for N22 meanwhile their total sugar concentration (TSC) were higher at control and at HNT at milk stage as compared to Quer. N22 maintained unaltered the spikelet sterility and 1000-grain weight across environments showing a consistent trend with its stem NSC translocation. Both genotypes showed similarity in some gas exchange and chlorophyll fluorescence performance suggesting unaffected photosystem II photochemistry, linear electron flux, and CO2 assimilation. Beyond indicating that source functioning was not the limiting factor for low TSC and starch in glucose levels found in N22 on seventh day after heading stage. Moreover, our data suggest that the higher translocation capacity shown by N22 can be involved in their lower spikelet sterility and 1000-grain weight stability across the environments. These results indicate that selecting genotypes with higher capacity to stem NSC translocation at HNT could lead to more grain yield stability in future climate scenarios.

Phenylalanine Ammonia-Lyase and Source-Flow-Sink Related Attributes in Rice Genotypes Subjected to High Night Temperatures

Phenylalanine ammonia-lyase (PAL) which is considered to be one of the main lines of cell acclimation against stress in plants, non-structural carbohydrates (NSC) accumulation and chlorophyll fluorescence parameters were quantified in two rice genotypes as a function of two temperature regimes: 22/30 °C (control) and 28/30 °C night/day (high night temperatures - HNT), imposed from heading to milk stage. The rice cultivars chosen were Nagina22 (N22) and BRS Querência (BRS-Quer), which are genotypes tolerant and sensitive to high temperatures, respectively. BRS-Quer genotype highlighted more sensitive responses maintaining higher PAL and peroxidase levels on seventh and twenty-first days after stress imposing. On the other hand, this genotype showed levels of fructose, glucose and sucrose decreasingly across stress period whether compared to N22. Both genotypes showed similarity for most of the chlorophyll fluorescence parameters. However, the photosynthesis induction curve highlighted that HNT caused decreases in some photochemical quenching of fluorescence as well as increases of non-phochemical quenching, affecting more prominently BRS-Quer genotype. N22 maintained unaltered the spikelet sterility and 1000-grain weight across temperature regimes showing a consistent trend with its stem NSC accumulation during stress period. The higher availability of soluble sugars shown by N22 at the end of stress period could be unloaded in spikelet formation and grain fillings contributing in their lower sterility rate and greater 1000-grain weight stability across the environments. These results indicate that selecting genotypes with higher capacity to stem NSC translocation beyond accumulation at HNT could lead to more grain yield stability in future climate scenarios.

High day- and night-time temperatures affect grain growth dynamics in contrasting rice genotypes.

Rice grain yield and quality are predicted to be highly vulnerable to global warming. Five genotypes including heat-tolerant and susceptible checks, a heat-tolerant near-isogenic line and two hybrids were exposed to control (31 °C/23 °C, day/night), high night-time temperature (HNT; 31 °C/30 °C), high day-time temperature (HDT; 38 °C/23 °C) and high day- and night-time temperature (HNDT; 38 °C/30 °C) treatments for 20 consecutive days during the grain-filling stage. Grain-filling dynamics, starch metabolism enzymes, temporal starch accumulation patterns and the process of chalk formation were quantified. Compensation between the rate and duration of grain filling minimized the impact of HNT, but irreversible impacts on seed-set, grain filling and ultimately grain weight were recorded with HDT and HNDT. Scanning electron microscopy demonstrated irregular and smaller starch granule formation affecting amyloplast build-up with HDT and HNDT, while a quicker but normal amylopast build-up was recorded with HNT. Our findings revealed temporal variation in the starch metabolism enzymes in all three stress treatments. Changes in the enzymatic activity did not derail starch accumulation under HNT when assimilates were sufficiently available, while both sucrose supply and the conversion of sucrose into starch were affected by HDT and HNDT. The findings indicate differential mechanisms leading to high day and high night temperature stress-induced loss in yield and quality. Additional genetic improvement is needed to sustain rice productivity and quality under future climates.

Meta-analysis and dose-response analysis of high temperature effects on rice yield and quality

Global warming is one of the biggest challenges for improving the productivity of rice crops in the future. In this study, a meta-analysis and a dose-response analysis were conducted with data collected from 95 publications to study the differential responses of physiological traits, yield components, and grain quality to high day and night temperatures in rice. Overall, grain yield was reduced by 39.6% (with 95% CI from −42.9% to −35.6%) under high temperatures, which was primarily caused by the decrease of seed set percentage. Yield reductions caused by high temperatures were associated with a decrease in photosynthesis and an increase in respiration. High temperatures affected grain quality by decreasing head rice percentage and increasing chalky rice rate and chalkiness. The reduction of grain yields under high day temperature was primarily caused by the reduction in seed set percentage. However, under high night temperature, the combination of decreased spikelet number per panicle, grain weight, and biomass production in addition to decreased seed set percentage contributed to the decline of grain yields. These results suggest that the differential effects of day and night warming on the processes that contribute to formation of rice yield should be considered when new rice cultivars are developed as a crop adaptation strategy for future global warming.

The Effects of Night-time Temperatures on Physiological and Biochemical Traits in Rice

High nighttime temperatures impair rice yield. Additionally, heat stress periods have increased during the last years in the rice areas of the tropics. The aim of this study was to physiologically characterize six genotypes of rice (a commercial cultivar (ʻF60ʼ) and five selected lines (ʻIR 1561ʼ, ʻFLO 2764ʼ, ʻLV447-1ʼ, ʻCT19021ʼ, and ʻLV1401ʼ) subjected to two nighttime temperatures (24 and 30 °C), based on different physiological traits. When the collar formed on leaf 6 of the main stem, one group of six plants in each genotype was subjected to 30 °C from 18:00 to 24:00 hours for eight days, while the other group remained at 24 °C. Differences were found in the interaction between genotype and nighttime temperatures, where a high night temperature reduced leaf photosynthesis by approximately 50% in all genotypes compared to the controls (20 µmol vs. 10 µmol CO2 m-2 s-1, respectively). In general, higher plant respiration was also observed in almost all genotypes when the plants were exposed to 30 °C. However, rice plants of the genotype ʻF60ʼ showed a constant respiration under two different night temperatures. A high nighttime temperature increased the electrolyte leakage and malondialdehyde content only in the ʻLV1401ʼ plants. Plant growth and Fv/Fm ratio were separately conditioned by the night temperature or the genotype factor. A lower total plant dry weight was found at 30 °C (620.36 mg) than in rice plants exposed to 24 °C (254.16 mg). The Fv/Fm ratio was slightly diminished at a high nighttime temperature. These results suggest that physiological variables, such as leaf photosynthesis, plant respiration, malondialdehyde content and leaf photosynthetic pigments, can be considered markers for characterizing tolerant genotypes in earlier growth phases during plant breeding programs.

Microclimate and air quality investigation in historic hilly urban areas: Experimental and numerical investigation in central Italy

Outdoor environmental comfort strongly affects the quality of life and depends on local microclimate phenomena. However, impact of local boundaries is still weakly studied in hilly urban historical layouts. Local microclimate variability and its influence on pedestrians’ comfort in selected hilly historical urban areas with varying local boundaries in term of vegetation, surface materials, urban density, and air quality, is investigated. To this aim, a field monitoring is carried out during summer in hilly dense built environment and numerical analysis is performed. Monitoring campaigns show how higher density and surface roughness in the urban historical area reduce daily temperature fluctuation up to 3°C, with higher night temperatures. Temperature discrepancies up to 5°C are detected compared to suburban greener area. Moreover, inverse correlation between sky-view factor and nighttime cooling is registered, with mean temperature variation up to 6.6°C. Numerical analysis shows different thermal comfort conditions within the same district, due to different local boundaries in terms of sky-view factor and surface materials properties. Maximum Predicted Mean Vote difference of 0.6 is detected in the same area. Findings demonstrate how impact of local boundaries needs to be accurately investigated, when analyzing quality of outdoor urban environment, to realistically predict citizens’ outdoor thermal conditions.

Quantitative iTRAQ-based proteomic analysis of rice grains to assess high night temperature stress.

Rice yield and quality are adversely affected by increasing global surface temperature, and are strongly attributed to high night temperature (HNT) than high daytime temperature. However, the molecular mechanism underlying the heat‐tolerant characteristics of rice remains unclear. In the present study, we compared the proteomes of heat‐tolerant and ‐sensitive lines of rice at early milky stage using an iTRAQ method. We have identified 38 differentially expressed proteins between the two lines, of which 32 proteins have been functionally annotated in NCBI and/or the UniProt database. These proteins were then classified into seven functional subgroups, which include signal transduction, transcript regulation, oxidation, defense response, transport, energy metabolism, and biosynthesis. Further analysis indicated that HNT stress could disrupt the redox equilibrium of plant cells, which in turn triggers the calcium‐dependent protein kinase and COP9 signalosome, thereby regulating downstream genes/proteins that are involved in the HNT response. The candidate proteins may provide genetic resources for the improvement of heat‐tolerant characteristics in rice, and the proposed model for signal transduction and transcriptional regulation may facilitate in the elucidation of the molecular mechanism underlying the response to HNT stress in rice.

High day–night transition temperature alters nocturnal starch metabolism in rice (Oryza sativa L.)

Transitory starch plays a vital role in maintenance respiration as its degradation products provide substrate for the night respiration. A study was conducted with two contrasting rice cultivars: Vandana (high night temperature susceptible) and Nagina 22 (high night temperature tolerant) by subjecting them to increase in transition temperature from anthesis to physiological maturity. Night respiration on plant area basis increased by 35% in Vandana at 5 days after anthesis but was unaffected in tolerant cultivar. A simultaneous 18% decrease in starch content was observed in the susceptible cultivar. An analysis of the starch-metabolizing enzymes showed that activity of β-amylase increased markedly in Vandana whereas both β and α-amylase decreased in Nagina 22 following high day to night transition temperature exposure. The level of starch breakdown product, maltose, increased in the susceptible cultivar but glucose levels declined in both the cultivars. Concurrently, expression of chloroplastic isoforms α-amylase OsAMY1, OsAMY2 and β-amylase OsBAM2 increased in Vandana. A lower accumulation of dry matter was recorded in the susceptible than the tolerant cultivar. Our study elucidated the regulatory role of transitory starch in supporting the high day to night transition temperature-induced night-time respiration which is mediated by the increased activity of β-amylase through enhanced expression of OsBAM2 in flag leaves of susceptible cultivar.

Synergistic Effects of a Night Temperature Shift and Methyl Jasmonate on the Production of Anthocyanin in Red Leaf Lettuce

The production of a secondary metabolite such as anthocyanin is coordinately regulated by plant intrinsic factors and influenced by multiple environmental factors. In red leaf lettuce, the red pigment component anthocyanin is important for the commercial value of the crop, but its synchronous regulation by multiple factors is not well understood. Here, we examined the synergistic effects of a night temperature shift and methyl jasmonate (MJ) on the production of anthocyanin in red leaf lettuce. Low or high night temperature treatment for 3 days just before harvesting induced the production of anthocyanin without affecting plant biomass. Temperature-dependent activation of anthocyanin accumulation was accelerated by treating with MJ. Night temperature shifts and MJ triggered oxidative stresses in leaves, as indicated by hydrogen peroxide accumulation and lipid peroxidation. Interestingly, these oxidative stresses were more evident in leaves simultaneously treated with both a high night temperature and MJ. The activity of the superoxide dismutase (SOD) was increased alongside the elevation of oxidative stress. Taken together, these results indicate that the combined treatment of a night temperature shift with MJ may accelerate anthocyanin production by increasing the levels of oxidative stress to the leaves of red leaf lettuce.

Altering Conidial Dispersal of Alternaria solani by Modifying Microclimate in Tomato Crop Canopy.

Early blight of tomato caused by Alternaria solani, is responsible for severe yield losses in tomato. The conidia survive on soil surface and old dry lower leaves of the plant and spread when suitable climatic conditions are available. Macroclimatic study reveals that highest inoculum concentration of Alternaria spores appeared in May 2012 to 2013 and lowest concentration during January 2012 to 2013. High night temperature positively correlated and significantly (P < 0.01) involved in conidial spore dispersal and low relative humidity (RH) displayed significant (P < 0.05) but negative correlation with conidial dispersal. The objective of the study was to modify microclimatic conditions of tomato crop canopy which may hamper conidial dispersal and reduce disease severity. We evaluated effect of marigold intercropping and plastic mulching singly and in consortia on A. solani conidial density, tomato leaf damage and microclimatic parameters as compar to tomato alone (T). Tomato-marigold intercropping–plastic mulching treatment (T + M + P) showed 35–39% reduction in disease intensity as compared to tomato alone. When intercropped with tomato, marigold served as barrier to conidial movement and plastic mulching prevented evapotranspiration and reduced the canopy RH that resulted in less germination of A. solani spores. Marigold intercropping and plastic mulching served successfully as physical barrier against conidial dissemination to diminish significantly the tomato foliar damage produced by A. solani.

Integrated analysis of rice transcriptomic and metabolomic responses to elevated night temperatures identifies sensitivity- and tolerance-related profiles.

Transcript and metabolite profiling were performed on leaves from six rice cultivars under high night temperature (HNT) condition. Six genes were identified as central for HNT response encoding proteins involved in transcription regulation, signal transduction, protein-protein interactions, jasmonate response and the biosynthesis of secondary metabolites. Sensitive cultivars showed specific changes in transcript abundance including abiotic stress responses, changes of cell wall-related genes, of ABA signaling and secondary metabolism. Additionally, metabolite profiles revealed a highly activated TCA cycle under HNT and concomitantly increased levels in pathways branching off that could be corroborated by enzyme activity measurements. Integrated data analysis using clustering based on one-dimensional self-organizing maps identified two profiles highly correlated with HNT sensitivity. The sensitivity profile included genes of the functional bins abiotic stress, hormone metabolism, cell wall, signaling, redox state, transcription factors, secondary metabolites and defence genes. In the tolerance profile, similar bins were affected with slight differences in hormone metabolism and transcription factor responses. Metabolites of the two profiles revealed involvement of GABA signaling, thus providing a link to the TCA cycle status in sensitive cultivars and of myo-inositol as precursor for inositol phosphates linking jasmonate signaling to the HNT response specifically in tolerant cultivars.

Plant Physiological, Morphological and Yield-Related Responses to Night Temperature Changes across Different Species and Plant Functional Types.

Land surface temperature over the past decades has shown a faster warming trend during the night than during the day. Extremely low night temperatures have occurred frequently due to the influence of land-sea thermal difference, topography and climate change. This asymmetric night temperature change is expected to affect plant ecophysiology and growth, as the plant carbon consumption processes could be affected more than the assimilation processes because photosynthesis in most plants occurs during the daytime whereas plant respiration occurs throughout the day. The effects of high night temperature (HNT) and low night temperature (LNT) on plant ecophysiological and growing processes and how the effects vary among different plant functional types (PFTs) have not been analyzed extensively. In this meta-analysis, we examined the effect of HNT and LNT on plant physiology and growth across different PFTs and experimental settings. Plant species were grouped according to their photosynthetic pathways (C3, C4, and CAM), growth forms (herbaceous, woody), and economic purposes (crop, non-crop). We found that HNT and LNT both had a negative effect on plant yield, but the effect of HNT on plant yield was primarily related to a reduction in biomass allocation to reproduction organs and the effect of LNT on plant yield was more related to a negative effect on total biomass. Leaf growth was stimulated at HNT and suppressed at LNT. HNT accelerated plants ecophysiological processes, including photosynthesis and dark respiration, while LNT slowed these processes. Overall, the results showed that the effects of night temperature on plant physiology and growth varied between HNT and LNT, among the response variables and PFTs, and depended on the magnitude of temperature change and experimental design. These findings suggest complexities and challenges in seeking general patterns of terrestrial plant growth in HNT and LNT. The PFT specific responses of plants are critical for obtaining credible predictions of the changes in crop production, plant community structure, vegetation dynamics, biodiversity, and ecosystem functioning of terrestrial biomes when asymmetric night temperature change continues.

High daytime temperature delays autumnal bud formation in Populus tremula under field conditions.

The effects of warming on autumnal growth cessation and bud formation in trees remain ambiguous due to contrasting observations between a range of studies under controlled conditions and field experiments. High night temperature has been reported to advance growth cessation and bud formation in several tree species grown under controlled conditions. On the other hand, some recent field experiments have shown that autumn warming delays bud formation, although the temperature parameters that could account for this effect have not been identified. In addition, dioecious species have been shown to respond differently to environmental change, and differential warming effects on the sexes have received limited attention, even more so in relation to phenology. In a data set including three separate field experiments employing either experimental warming or an elevational gradient, we tested the effect of different temperature parameters on apical, vegetative bud formation and transitions between bud stages in female and male clones of Eurasian aspen (Populus tremula). Increased temperature was found to delay bud formation, and this process was best explained by maximum daily temperature. Males were significantly delayed compared with females in forming green closed buds, a process best explained by mean 24 h temperature. Bud maturation was best explained by mean daytime temperature, and buds matured significantly faster in males than in females, possibly explaining why females and males did not differ in terms of overall bud formation. In conclusion, our data show that delayed bud formation in Eurasian aspen during autumn can be attributed to the effect of high temperature, and this effect is in contrast to most of the evidence from studies of bud development in controlled environments.

Post-flowering night respiration and altered sink activity account for high night temperature-induced grain yield and quality loss in rice (Oryza sativa L.).

High night temperature (HNT) is a major constraint to sustaining global rice production under future climate. Physiological and biochemical mechanisms were elucidated for HNT-induced grain yield and quality loss in rice. Contrasting rice cultivars (N22, tolerant; Gharib, susceptible; IR64, high yielding with superior grain quality) were tested under control (23°C) and HNT (29°C) using unique field-based tents from panicle initiation till physiological maturity. HNT affected 1000 grain weight, grain yield, grain chalk and amylose content in Gharib and IR64. HNT increased night respiration (Rn) accounted for higher carbon losses during post-flowering phase. Gharib and IR64 recorded 16 and 9% yield reduction with a 63 and 35% increase in average post-flowering Rn under HNT, respectively. HNT altered sugar accumulation in the rachis and spikelets across the cultivars with Gharib and IR64 recording higher sugar accumulation in the rachis. HNT reduced panicle starch content in Gharib (22%) and IR64 (11%) at physiological maturity, but not in the tolerant N22. At the enzymatic level, HNT reduced sink strength with lower cell wall invertase and sucrose synthase activity in Gharib and IR64, which affected starch accumulation in the developing grain, thereby reducing grain weight and quality. Interestingly, N22 recorded lower Rn-mediated carbon losses and minimum impact on sink strength under HNT. Mechanistic responses identified will facilitate crop models to precisely estimate HNT-induced damage under future warming scenarios.

Exogenously Applied Plant Growth Regulators Enhance the Morpho-Physiological Growth and Yield of Rice under High Temperature.

A 2-year experiment was conducted to ascertain the effects of exogenously applied plant growth regulators (PGR) on rice growth and yield attributes under high day (HDT) and high night temperature (HNT). Two rice cultivars (IR-64 and Huanghuazhan) were subjected to temperature treatments in controlled growth chambers and four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA), and triazoles (Tr) were applied. High temperature severely affected rice morphology, and also reduced leaf area, above-, and below-ground biomass, photosynthesis, and water use efficiency, while increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more detrimental for grain formation and yield. The Huanghuazhan performed better than IR-64 under high temperature stress with better growth and higher grain yield. Exogenous application of PGRs was helpful in alleviating the adverse effects of high temperature. Among PGR combinations, the Vc+Ve+MejA+Br was the most effective treatment for both cultivars under high temperature stress. The highest grain production by Vc+Ve+MejA+Br treated plants was due to enhanced photosynthesis, spikelet fertility and grain filling, which compensated the adversities of high temperature stress. Taken together, these results will be of worth for further understanding the adaptation and survival mechanisms of rice to high temperature and will assist in developing heat-resistant rice germplasm in future.

Responses of Rapid Viscoanalyzer Profile and Other Rice Grain Qualities to Exogenously Applied Plant Growth Regulators under High Day and High Night Temperatures.

High-temperature stress degrades the grain quality of rice; nevertheless, the exogenous application of plant growth regulators (PGRs) might alleviate the negative effects of high temperatures. In the present study, we investigated the responses of rice grain quality to exogenously applied PGRs under high day temperatures (HDT) and high night temperatures (HNT) under controlled conditions. Four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA) and triazoles (Tr) were exogenously applied to two rice cultivars (IR-64 and Huanghuazhan) prior to the high-temperature treatment. A Nothing applied Control (NAC) was included for comparison. The results demonstrated that high-temperature stress was detrimental for grain appearance and milling qualities and that both HDT and HNT reduced the grain length, grain width, grain area, head rice percentage and milled rice percentage but increased the chalkiness percentage and percent area of endosperm chalkiness in both cultivars compared with ambient temperature (AT). Significantly higher grain breakdown, set back, consistence viscosity and gelatinization temperature, and significantly lower peak, trough and final viscosities were observed under high-temperature stress compared with AT. Thus, HNT was more devastating for grain quality than HDT. The exogenous application of PGRs ameliorated the adverse effects of high temperature in both rice cultivars, and Vc+Ve+MejA+Br was the best combination for both cultivars under high temperature stress.

Post-anthesis warm nights reduce grain weight in field-grown wheat and barley

Wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) crops are exposed to warm nights during their growing seasons and this trend is unlikely to change. The aim of this work was to evaluate the effect of higher post-anthesis night temperatures on field-grown crop yield, focusing on final grain weight determination. Experiments combined: (i) two well-adapted crops with similar phenology: bread wheat and two-row malting barley, under (ii) two temperature regimes: ambient and high night temperatures from 10days after anthesis to physiological maturity during (iii) two contrasting growing seasons in terms of radiation and temperature: late sowing in 2011 and early sowing in 2013. The night temperature increase (ca. 4.1°C) was achieved using purpose-built heating chambers placed on the crop at 7pm and removed at 7am every day during the heating period. Across growing seasons and crops, the average minimum temperature during that period ranged from 14.3°C to 21.9°C. Thousand grain weight was reduced by ca. 3% per °C of night temperature increase, similarly for wheat and barley, causing a grain yield reduction of ca. 4% per °C. An accelerated development under high night temperatures led to a shorter effective grain filling period, reducing the final grain weight. The lack of consistent impact on source availability between crops and seasons, measured as senescence and stem water soluble carbohydrates, as well as a similar impact in magnitude and direction on individual grain weight for different grain positions along wheat or barley spikes, suggest that the negative effects of warm nights on grain weight were directly related to processes within the grain itself.