Xiangnan Li

Induction of chilling tolerance in wheat during germination by pre-soaking seed with nitric oxide and gibberellin

Chilling depresses seed germination and seedling establishment, and is one major constraint to grain yield formation in late sown winter wheat. Seeds of winter wheat (Triticum aestivum L.) were separately pre-soaked with sodium nitroprusside (SNP, as nitric oxide donor) and Gibberellic acid (GA3) before germination and then germinated under low temperature. SNP and GA3 pre-treatment increased seed germination rate, germination index, weights and lengths of coleoptile and radicle, while they decreased mean germination time and weight of seeds germinating under low temperature. Exogenous NO and GA3 increased seed respiration rate and promoted starch degradation along with increased amylase activities. In addition, efficient antioxidant systems were activated by NO, and which effectively reduced concentrations of malondialdehyde and hydrogen peroxide (H2O2). Seedling growth was also enhanced by exogenous NO and GA3 as a result of improved seed germination and maintenance of better reactive oxygen species homeostasis in seedling growing under chilling temperatures. It is indicated that exogenous NO was more effective than GA3 in alleviating chilling stress during seed germination and seedling establishment in wheat.

Melatonin enhances cold tolerance in drought-primed wild-type and abscisic acid-deficient mutant barley.

Melatonin is involved in multiple plant developmental processes and various stress responses. To explore the roles of melatonin played as well as its association with abscisic acid (ABA) in a process of drought priming‐induced cold tolerance (DPICT), a wild‐type barley and its ABA‐deficient mutant Az34 counterpart were selected for comparison, in which the effects of melatonin application (either foliarly or rhizospherically) and/or drought priming on the cold tolerance of both types of barleys were systematically investigated. It was demonstrated that the early drought priming induced an increase of endogenous melatonin production, which is not ABA dependent. In addition, exogenously applied melatonin resulted in higher ABA concentration in the drought‐primed plants than in the nonprimed plants when exposed to cold stress, indicating that ABA responded in a drought‐dependent manner. The interplay of melatonin and ABA leads to plants maintaining better water status. Drought priming‐induced melatonin accumulation enhanced the antioxidant capacity in both chloroplasts and mitochondria, which sustained the photosynthetic electron transport in photosynthetic apparatus of the plants under cold stress. These results suggest that the exogenous melatonin application enhances the DPICT by modulating subcellular antioxidant systems and ABA levels in barley.

Physiological, proteomic and transcriptional responses of wheat to combination of drought or waterlogging with late spring low temperature

Spring low temperature events affect winter wheat (Triticum aestivum L.) during late vegetative or reproductive development, exposing plants to a subzero low temperature stress when winter hardening is lost. The increased climatic variability results in wheat being exposed to more frequent adverse impacts of combined low temperature and water stress, including drought and waterlogging. The responses of potted wheat plants cultivated in climatic chambers to these environmental perturbations were investigated at physiological, proteomic and transcriptional levels. At the physiological level, the depressed carbon (C) assimilation induced by the combined stresses was due mainly to stomatal closure and damage of photosynthetic electron transport. Biochemically, the adaptive effects of early moderate drought or waterlogging stress were associated with the activation of antioxidant enzyme system in chloroplasts and mitochondria of leaf under low temperature. Further proteomic analysis revealed that the oxidative stress defence, C metabolism and photosynthesis related proteins were modulated by the combined low temperature and water stress. Collectively, the results indicate that impairment of photosynthesis and C metabolism was responsible for the grain yield loss in winter wheat under low temperature in combination with severe drought or waterlogging stress. In addition, prior mild drought or waterlogging contributed to the homeostasis of oxidative metabolism and relatively better photosynthesis, and hence to less grain yield loss under later spring low temperature stress.

Melatonin alleviates low PS I limited carbon assimilation under elevated CO2 and enhances the cold tolerance of offspring in chlorophyll b-deficient mutant wheat

Melatonin is involved in the regulation of carbohydrate metabolism and induction of cold tolerance in plants. The objective of this study was to investigate the roles of melatonin in modulation of carbon assimilation of wild‐type wheat and the Chl b‐deficient mutant ANK32B in response to elevated CO2 concentration ([CO2]) and the transgenerational effects of application of exogenous melatonin (hereafter identified as melatonin priming) on the cold tolerance in offspring. The results showed that the melatonin priming enhanced the carbon assimilation in ANK32B under elevated [CO2], via boosting the activities of ATPase and sucrose synthesis and maintaining a relatively higher level of total chlorophyll concentration in leaves. In addition, melatonin priming in maternal plants at grain filling promoted the seed germination in offspring by accelerating the starch degradation and improved the cold tolerance of seedlings through activating the antioxidant enzymes and enhancing the photosynthetic electron transport efficiency. These findings suggest the important roles of melatonin in plant response to future climate change, indicating that the melatonin priming at grain filling in maternal plants could be an effective approach to improve cold tolerance of wheat offspring at seedling stage.

Melatonin Improves the Photosynthetic Carbon Assimilation and Antioxidant Capacity in Wheat Exposed to Nano-ZnO Stress

The release of nanoparticles into the environment is inevitable, which has raised global environmental concern. Melatonin is involved in various stress responses in plants. The present study investigated the effects of melatonin on photosynthetic carbon (C) assimilation and plant growth in nano-ZnO stressed plants. It was found that melatonin improved the photosynthetic C assimilation in nano-ZnO stressed wheat plants, mainly due to the enhanced photosynthetic energy transport efficiency, higher chlorophyll concentration and higher activities of Rubisco and ATPases. In addition, melatonin enhanced the activities of antioxidant enzymes to protect the photosynthetic electron transport system in wheat leaves against the oxidative burst caused by nano-ZnO stress. These results suggest that melatonin could improve the tolerance of wheat plants to nano-ZnO stress.

Drought Stress Memory and Drought Stress Tolerance in Plants: Biochemical and Molecular Basis

Drought is one of the major environmental factors limiting plant growth and development. Drought stress tolerance in plants involves diverse and multiple physiological and molecular mechanisms. Priming and drought stress memory are key processes, by which plant may increase the tolerance to subsequent drought events. Stress memory involves multiple modifications at physiological, proteomic, transcriptional levels and epigenetic mechanisms. In this chapter, we summarized recent advancements in physiological, biochemical, and molecular studies related to drought priming and its effect on drought tolerance in plants. The mechanisms of drought stress memory and the possible priming-induced cross-tolerance to other abiotic stresses are discussed.

Salt response of photosynthetic electron transport system in wheat cultivars with contrasting tolerance

Soil salinity significantly decreases the photosynthetic efficiency and plant growth in wheat (Triticum aestivum L.). However, sensitivity of the photosynthetic electron transport system of wheat in relation with salt stress is unclear. Two wheat cultivars with contrasting salt tolerance were exposed to soil salinity, and the physiological responses and performance of photosynthetic electron system were investigated. The depressed photosynthetic carbon assimilation was mainly caused by stomatal closure and lower photosynthetic electron transport efficiency. Under salt stress, the salt-resistant cv. YN19 had higher efficiency in photosynthetic electron transport, hence maintaining higher photosynthetic rate under salt stress, compared with the salt-sensitive cv. JM22. In addition, the parameters derived from fast chlorophyll a fluorescence induction curve, i.e. the quantum yield for electron transport (φEo) and the probability that an electron moves futher than QA (ψEo), can be used as indicators for rapid screening of wheat cultivars tolerant to soil salinity.

Soil warming enhances the hidden shift of elemental stoichiometry by elevated CO2 in wheat.

Increase in atmospheric CO2 concentration ([CO2]) and associated soil warming along with global climate change are expected to have large impacts on grain mineral nutrition in wheat. The effects of CO2 elevation (700 μmol l−1) and soil warming (+2.4 °C) on K, Ca and Mg concentrations in the xylem sap and their partitioning in different organs of wheat plant during grain filling were investigated. Results showed that the combination of elevated [CO2] and soil warming improved wheat grain yield, but decreased plant K, Ca and Mg accumulation and their concentrations in the leaves, stems, roots and grains. The reduced grain mineral concentration was attributed to the lowered mineral uptake as exemplified by both the decreased stomatal conductance and mineral concentration in the xylem sap. These findings suggest that future higher atmospheric [CO2] and warmer soil conditions may decrease the dietary availability of minerals from wheat crops. Breeding wheat cultivars possessing higher ability of mineral uptake at reduced xylem flux in exposure to climate change should be a target.

Cold Priming Induced Tolerance to Subsequent Low Temperature Stress is Enhanced by Melatonin Application during Recovery in Wheat

Cold priming can alleviate the effects of subsequent cold stress on wheat plant growth. Melatonin plays a key role in cold stress response in plants. In this study, the effects of foliar melatonin application during recovery on the cold tolerance of cold primed wheat plants were investigated. It was found that both melatonin and cold priming increased the photosynthetic rate and stomatal conductance, enhanced the activities of antioxidant enzymes, and altered the related gene expressions in wheat under cold stress. Melatonin application is helpful for the photosynthetic carbon assimilation and membrane stability of the cold primed plants under cold stress. These results suggested that foliar melatonin application during recovery enhanced the cold priming induced tolerance to subsequent low temperature stress in wheat.

Salicylic Acid Alleviates Aluminum Toxicity in Soybean Roots through Modulation of Reactive Oxygen Species Metabolism

As an important signal molecule, salicylic acid (SA) improves plant tolerance to aluminum (Al) stress. The objective of this study was to investigate the effects of exogenous SA application on the dynamics of endogenous SA and reactive oxygen species in soybean (Glycine max L.) exposed to Al stress. The roots of soybean seedlings were exposed to a combination of AlCl3 (30 μM) and SA (10 μM)/PAC (100 μM, paclobutrazol, SA biosynthesis inhibitor) for 3, 6, 9, and 12 h. Al stress induced an increase in endogenous SA concentration in a time-dependent manner, also verified by the up-regulated expression of GmNPR1, an SA-responsive gene. Al stress increased the activities of phenylalanine ammonia-lyase (PAL) and benzoic acid 2-hydroxylase (BA2H), and the contents of SA, O2- and malondialdehyde (MDA) in the root apex. The application of exogenous SA increased PAL and BA2H, and reduced O2- and MDA contents in soybean roots under Al stress. PAC inhibited the SA induced increase in BA2H activity. In addition, the SA application resulted in a rapid increase in hydrogen peroxide (H2O2) concentration under Al stress, followed by a sharp decrease. Compared with the plants exposed to Al alone, Al+SA plants possessed higher activities of superoxide dismutase, peroxidase, and ascorbate peroxidase, and lower catalase activity, indicating that SA alleviated Al-induced oxidative damage. These results suggested that PAL and BA2H were involved in Al-induced SA production and showed that SA alleviated the adverse effects of Al toxicity by modulating the cellular H2O2 level and the antioxidant enzyme activities in the soybean root apex.