Effects of high temperature stress during anthesis and grain filling periods on photosynthesis, lipids and grain yield in wheat

BACKGROUND

Short episodes of high temperature (HT) stress during reproductive stages of development cause significant yield losses in wheat (Triticum aestivum L.). Two independent experiments were conducted to quantify the effects of HT during anthesis and grain filling periods on photosynthesis, leaf lipidome, and yield traits in wheat. In experiment I, wheat genotype Seri82 was exposed to optimum temperature (OT; 22/14 °C; day/night) or HT (32/22 °C) for 14 d during anthesis stage. In experiment II, the plants were exposed to OT or HT for 14 d during the grain filling stage. During the HT stress, chlorophyll index, thylakoid membrane damage, stomatal conductance, photosynthetic rate and leaf lipid composition were measured. At maturity, grain yield and its components were quantified.

RESULTS

HT stress during anthesis or grain filling stage decreased photosynthetic rate (17 and 25%, respectively) and grain yield plant^- 1 (29 and 44%, respectively), and increased thylakoid membrane damage (61 and 68%, respectively) compared to their respective control (OT). HT stress during anthesis or grain filling stage increased the molar percentage of less unsaturated lipid species [36:5- monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)]. However, at grain filling stage, HT stress decreased the molar percentage of more unsaturated lipid species (36:6- MGDG and DGDG). There was a significant positive relationship between photosynthetic rate and grain yield plant^- 1, and a negative relationship between thylakoid membrane damage and photosynthetic rate.

CONCLUSIONS

The study suggests that maintaining thylakoid membrane stability, and seed-set per cent and individual grain weight under HT stress can improve the photosynthetic rate and grain yield, respectively.

Alien chromosome segment from Aegilops speltoides and Dasypyrum villosum increases drought tolerance in wheat via profuse and deep root system

BACKGROUND

Recurrent drought associated with climate change is a major constraint to wheat (Triticum aestivum L.) productivity. This study aimed to (i) quantify the effects of addition/substitution/translocation of chromosome segments from wild relatives of wheat on the root, physiological and yield traits of hexaploid wheat under drought, and (ii) understand the mechanism(s) associated with drought tolerance or susceptibility in wheat-alien chromosome lines.

METHODS

A set of 48 wheat-alien chromosome lines (addition/substitution/translocation lines) with Chinese Spring background were used. Seedling root traits were studied on solid agar medium. To understand the influence of drought on the root system of adult plants, these 48 lines were grown in 150-cm columns for 65 d under full irrigation or withholding water for 58 d. To quantify the effect of drought on physiological and yield traits, the 48 lines were grown in pots under full irrigation until anthesis; after that, half of the plants were drought stressed by withholding water for 16 d before recording physiological and yield-associated traits.

RESULTS

The alien chromosome lines exhibited altered root architecture and decreased photochemical efficiency and seed yield and its components under drought. The wheat-alien chromosome lines T5DS·5S#3L (TA5088) with a chromosome segment from Aegilops speltoides (5S) and T5DL.5 V#3S (TA5638) with a chromosome segment from Dasypyrum villosum (5 V) were identified as drought tolerant, and the drought tolerance mechanism was associated with a deep, thin and profuse root system.

CONCLUSIONS

The two germplasm lines (TA5088 and TA5638) could be used in wheat breeding programs to improve drought tolerance in wheat and understand the underlying molecular genetic mechanisms of root architecture and drought tolerance.

Quantifying pearl millet response to high temperature stress: thresholds, sensitive stages, genetic variability and relative sensitivity of pollen and pistil

The objectives were to (1) quantify high temperature (HT) stress impacts at different growth stages (season long, booting to seed-set and booting to maturity) on various yield components; (2) identify the most sensitive stage(s) to short episodes of HT stress during reproductive development; (3) understand the genetic variations for HT stress tolerance based on cardinal temperatures for pollen germination; and (4) determine relative sensitivity of pollen and pistil to HT stress and associated tolerance or susceptible mechanisms in pearl millet. High temperature stress (≥36/26°C) imposed at different stages and durations caused decrease in number of seeds, individual seed weight and seed yield. Two periods (10-12 days and 2-0 days before anthesis) were identified as most sensitive to short episodes of stress, causing maximum decreases in pollen germination percentage and seeds numbers. HT stresses of ≥36/26°C results in floret sterility. Pistils were relatively more sensitive than pollen grains, causing decreased number of seeds and seed yield. HT stress increased the reactive oxygen species contents and decreased the activity of the antioxidant enzymes in both pollen and pistils. Under HT stress, pistils had relatively higher reactive oxygen species and lower antioxidant enzymes activity compared with pollen grains, which explains greater susceptibility of pistils.

Sensitivity of sorghum pollen and pistil to high-temperature stress

High temperature (HT) decreases seed set percentage in sorghum (Sorghum bicolor [L.] Moench). The relative sensitivity of pollen and particularly pistil and the mechanistic response that induces tolerance or susceptibility to HT are not well known and hence are the major objectives of this research. The male sterile (ATx399) and fertile (RTx430) lines were exposed to 30/20 °C (optimum temperature), 36/26 °C (HT1 ), and 39/29 °C (HT2 ) from the start of booting to seed set in a controlled environment. Similarly, in the field, HT stress was imposed using heat tents. HT stress decreased pollen germination. Relatively high levels of reactive oxygen species and decreased antioxidant enzyme activity and phospholipid unsaturation were observed in pollen compared to pistil under HT. The severe cell organelle damage was observed in pollen and pistil at 36/26 and 39/29 °C, respectively. The seed set percentage was higher in HT-stressed pistil pollinated with optimum-temperature pollen. Direct and reciprocal crosses indicate that pollen was more sensitive with larger decreases in seed set percentage than pistil under HT stress. The negative impact was greater in pollen than pistil at lower temperatures. Overall, pollen was more sensitive than pistil to HT stress because it is more susceptible to oxidative damage than pistil.

Decreased photosynthetic rate under high temperature in wheat is due to lipid desaturation, oxidation, acylation, and damage of organelles

BACKGROUND

High temperature is a major abiotic stress that limits wheat (Triticum aestivum L.) productivity. Variation in levels of a wide range of lipids, including stress-related molecular species, oxidative damage, cellular organization and ultrastructural changes were analyzed to provide an integrated view of the factors that underlie decreased photosynthetic rate under high temperature stress. Wheat plants of cultivar Chinese Spring were grown at optimum temperatures (25/15 °C, maximum/minimum) until the onset of the booting stage. Thereafter, plants were exposed to high temperature (35/25 °C) for 16 d.

RESULTS

Compared with optimum temperature, a lower photosynthetic rate was observed at high temperature which is an interplay between thylakoid membrane damage, thylakoid membrane lipid composition, oxidative damage of cell organelle, and stomatal and non-stomatal limitations. Triacylglycerol levels were higher under high temperature stress. Polar lipid fatty acyl unsaturation was lower at high temperature, while triacylglycerol unsaturation was the same at high temperature and optimum temperature. The changes in lipid species indicates increases in activities of desaturating, oxidizing, glycosylating and acylating enzymes under high temperature stress. Cumulative effect of high temperature stress led to generation of reactive oxygen species, cell organelle and membrane damage, and reduced antioxidant enzyme activity, and imbalance between reactive oxygen species and antioxidant defense system.

CONCLUSIONS

Taken together with recent findings demonstrating that reactive oxygen species are formed from and are removed by thylakoid lipids, the data suggest that reactive oxygen species production, reactive oxygen species removal, and changes in lipid metabolism contribute to decreased photosynthetic rate under high temperature stress.

High-Temperature Stress Alleviation by Selenium Nanoparticle Treatment in Grain Sorghum

The role of selenium nanoparticles (Se-NPs) in the mitigation of high-temperature (HT) stress in crops is not known. The uptake, toxicity and physiological and biological effects of Se-NPs under HT were investigated in grain sorghum [Sorghum bicolor (L.) Moench]. Se-NPs of size 10-40 nm were synthesized and characterized to indicate nanocrystalline structure. A toxicity assay showed that Se-NPs concentration inducing 50% cell mortality (TC50) was 275 mg L^-1. Translocation study indicated that Se-NPs can move from root to shoot of sorghum plants. Foliar spray of 10 mg L^-1 Se-NPs during the booting stage of sorghum grown under HT stress stimulated the antioxidant defense system by enhancing antioxidant enzymes activity. Furthermore, it decreased the concentration of signature oxidants. Se-NPs facilitated higher levels of unsaturated phospholipids. Se-NPs under HT stress improved the pollen germination percentage, leading to a significantly increased seed yield. The increased antioxidant enzyme activity and decreased content of oxidants in the presence of Se-NPs were greater under HT (38/28 °C) than under optimum temperature conditions (32/22 °C). In conclusion, Se-NPs can protect sorghum plants by enhanced antioxidative defense system under HT stress.

Selenium protects sorghum leaves from oxidative damage under high temperature stress by enhancing antioxidant defense system

Oxidative stress is commonly induced when plants are grown under high temperature (HT) stress conditions. Selenium often acts as an antioxidant in plants; however, its role under HT-induced oxidative stress is not definite. We hypothesize that selenium application can partly alleviate HT-induced oxidative stress and negative impacts of HT on physiology, growth and yield of grain sorghum [Sorghum bicolor (L.) Moench]. Objectives of this study were to investigate the effects of selenium on (a) leaf photosynthesis, membrane stability and antioxidant enzymes activity and (b) grain yield and yield components of grain sorghum plants grown under HT stress in controlled environments. Plants were grown under optimal temperature (OT; 32/22°C daytime maximum/nighttime minimum) from sowing to 63 days after sowing (DAS). All plants were foliar sprayed with sodium selenate (75mgL(-1)) at 63 DAS, and HT stress (40/30°C) was imposed from 65 DAS through maturity. Data on physiological, biochemical and yield traits were measured. High temperature stress decreased chlorophyll content, chlorophyll a fluorescence, photosynthetic rate and antioxidant enzyme activities and increased oxidant production and membrane damage. Decreased antioxidant defense under HT stress resulted in lower grain yield compared with OT. Application of selenium decreased membrane damage by enhancing antioxidant defense resulting in higher grain yield. The increase in antioxidant enzyme activities and decrease in reactive oxygen species (ROS) content by selenium was greater in HT than in OT. The present study suggests that selenium can play a protective role during HT stress by enhancing the antioxidant defense system.

Nitrophenolates spray can alter boll abscission rate in cotton through enhanced peroxidase activity and increased ascorbate and phenolics levels

Field studies were conducted from 2002 to 2005 to evaluate foliar spray of Atonik (a plant growth regulator (PGR) containing nitrophenolates) on cotton boll abscission rate by assessing various reactive oxygen species (ROS) contents, antioxidant content and antioxidant enzyme activity from 1 to 9 days after anthesis (DAA). The result indicated that the nitrophenolate spray reduced hydrogen peroxide (H(2)O(2)), superoxide anion (O(2)(-)) accumulation, lipid peroxidation (malondialdehyde--MDA), lipoxygenase (LOX) activity and membrane permeability relative to the control. Antioxidant enzyme activity (superoxide dismutase, SOD; ascorbate peroxidase, APX; peroxidase, POX; glutathione peroxidase, GSH-Px) was significantly increased by the nitrophenolate spray. The POX (217%) and GSH-Px (242%) activities were enhanced compared with APX (7.7%) activity at 9 DAA. Enhanced accumulation of ascorbate (245%), phenol (253%) and proline (150%) was observed in nitrophenolate-sprayed plants compared with control at 9 DAA. Because ascorbate content is increased by higher dehydroascorbate reductase (DHAR) enzyme activity, the ascorbate was able to replenish reducing equivalents to phenoxyl radicals, resulting in an increase of phenolic compounds. The increased phenolic acid content may be involved in scavenging the ROS produced in developing cotton boll. The role of DHAR and glutathione reductase (GR) in keeping higher levels of reduced ascorbate and low levels of endogenous H(2)O(2) in the developing cotton boll may be the prerequisite for boll retention. Based on the present work, we conclude that nitrophenolate-sprayed plants counteracted the deleterious effects of ROS by the peroxide/phenolics/ascorbate system, which causes reduced boll abscission and increased yield.