| Wheat (Tritivum aestivum, L) is the second food crop in China and its yield impacts not noly people's living standards but also national economic development directly. During grain filling stage, wheat plants often suffer from heat and high irradiation stress, which causes damage to photosynthetic apparatus and early senescence of leaves. As a result, grain yield declines due to organic nutrition deficiency. In this paper, we studied effects of SA on antioxidant metabolism, osmotic adjustment,membrane stability, photosynthetic rate and the chloroplast psbA gene expression of wheat leaves under heat and high-light stress.The aim is to clarify its role in protection of the photosynthetic apparatus and provide theoretical basis for increasing resistance of wheat leaves to heat and high-light stress. The experiments were conducted on experimental farm of Henan Agricultual University. Wheat seeds were planted in pots, sand plates and field respectively. The main results are as follows:1 Exogenous SA promoted psbA gene expression in wheat leaves under heat and high light stress.Heat and high light stress led to decrease of psbA gene expression, spraying SA can inhibit the high-temperature light-induced decrease of psbA gene expression, reducing the stress of wheat photoinhibition. Dark so that psbA gene restored the expression of a rapid recovery to near pre-stress levels, the effective protection of the PSⅡreaction center from destruction, safeguarding the effective functioning of the plant photosynthetic apparatus. Between the effects of concentration more significantly, 0.3mmol·L-1 of the SA role best.2 Exogenous SA increased the active oxygen scavenging capacity of wheat leaves under high temperature and strong light stress.Because SOD activity is induced by its substrate concentration, in the early stages of stress, SOD activity increased, but with the increase in stress time and stress levels, SOD activity declined sharply. APX activity had similar trend with SOD. Although spraying SA did not change the trend of SOD and APX activity, SOD and APX activity in the SA-pretreated leaves was always higher than the that of control. Meanwhile, Decrease in CAT activity was inhibited by SA. It was suggested that SA played a protective effect to leaves against oxidant injury. In 3 concentrations used in the experiment, 0.3mmol·L-1 of the SA had the best effect.3 Exogenous SA increased the ability of osmotic adjustment in wheat leaves under heat and strong light stress.Plant stress resistance and body substances such as free proline and proteins closely related. The foliar application of SA increased contents of proline in wheat leaves.Spraying SA on wheat leaves increased the accumulation of free proline under heat and high light stress. At the subsequent recovery stage, SA can effectively inhibit the reduction of proline content. The plant can directly be involved in the process of adapting the adversity by increasing the synthesis of soluble proteins in adversity conditions. Spraying SA on leaves played the role of promoting the proteins synthesis at the beginning of stress, and performed the function of controlling the degradation of them with the stress strengthening. The results illuminated that, under drought stress, spraying SA on leaves of wheat leaves can maintain the content of proteins by promoting the new of them synthesis or controlling some of them degradation, which can increased the hydrophilicity of cell and indirectly improved the drought-resistant ability of of wheat leaves. The concentration effects among the treatment were obvious, but 0.3mmol/L was the best concentration.4 Exogenous SA increased the potential and the efficiency of photosynthesis in wheat leaves under heat and strong light stress.The results showed that heat and high irradiance stress led to disruption of photosynthetic electron transport, decrease of PSⅡphotochemical efficiency, inactivation of PSⅡreaction center and reduction of net photosynthetic rate.Withstand high light stress in wheat, before spraying the right amount of SA, the effective suppression of the stress on the D1 protein damage, thereby maintaining a high photosynthetic rate. After 3h of recovery in dark, the photosynthetic rate of SA treatment recovered, but those in water-treated leaves did not. It was indicated that inactivation was reversible in SA treatment and irreversible in water treatment. Briefly, exogenous SA increased the potential and the efficiency of photosynthesis in wheat leaves under high temperature and strong light stress .In brief, exogenous SA can increase proline and soluble protein contents of wheat leaves, enhance stability of membrane lipids and reduce electrolyte leakage under heat and strong light stress.On the other hand, exogenous SA can increase defensive enzymes (SOD and APX) activity in wheat leaves under high light stress. Due to higher ROS scavenging ability, damage to psbA gene expression was decreased by SA. Therefore, high photosynthetic effeciency was maintained in SA-pretreated leaves. |
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