Effects Of Ethylene On The Tolerance Of Wheat To Booting And Flowering Waterlogging Stress And Its Mechanism Physiological

Waterlogging is one of the major natural disasters of the downstream plain of the Yangtze River, the wheat production area in China. Booting stage is considered to be wheat moisture damage critical period as well as flowering, in which waterlogging leads to heavy reduction of wheat yield. Ethylene is an important plant regulatory substance under adversity conditions, such as induces the formation of aerenchyma under waterlogging stress, influences the activity of antioxidant enzymes and so on. In this study, wheat plants (Yangmai 16) were sprayed exogenous ethephon, ethylene promoter(ACC), ethylene inhibitor(AOA) respectively as pretreatment at two stages (booting stage and flowering stage), and then followed a waterlogging stress in a pot experiment,7-day for booting stage, 10-day for flowering. The effects of exogenous ethephon, ACC and AOA pretreatment on endogenous ethylene release rate, photosynthesis, membrane lipid peroxidation of flag leaf, grain yield and nitrogen accumulation and remobilization under booting and flowering waterlogging stress were investigated in order to elucidate its physiological mechanisms for providing theoretical basis in wheat production. The main results were as follows:1. Ethylene improved grain yield under waterlogging stress, promoting grain nitrogen accumulation, reducing the plant height under booting waterlogging stress. The results showed that spraying ACC increased grain yield under flowering waterlogging stress mainly by improving 1000-kernel weight and spike number. High endogenous ethylene content induced wheat tillering, decreased spike grain number significantly under booting waterlogging stress, grain yield reduced finally. However, by prolonging leaf stay green time, ethylene increased grain nitrogen accumulation under flowering waterlogging stress. Spraying ACC or inhibited ethylene produce improved NRA of leaf sheaths, glume and rachis and each organ NRR, enhanced grain nitrogen accumulation in booting stage, In addition, under booting waterlogging stress, exogenous ethylene significantly reduced plant height, and contrasted ACC, ethephon had more effect.2. Ethylene participated in the regulation of the wheat stomatal movement, H2O2 could be the second messenger in guard cells ethylene signal. Exogenous ethylene increased the endogenous ethylene release rate of wheat flag leaf and root under waterlogging stress. The sensitive degree of plant induced by ethylene varies along with the growth period, the vegetative organs, flowering stage was greater than booting stage, leaf than root, and the effect of ethephon was stronger than ACC. High concentration ethylene further aggravated the wheat flag leaf chlorophyll degradation as well as exogenous substances preprocessing have less effect on the actual photochemical efficiency. Maybe, Ethylene affect wheat leaf photosynthesis under waterlogged stress mainly was not in the stomatal factors. Compared with waterlogging treatment, appropriate concentration ethylene increased the endogenous ethylene release rate of wheat flag leaf, reduced H2O2 production under booting waterlogged stress, relieved the stress of the wet leaf stomatal conductance decreased, kept the stomata opened, improved the wheat flag leaf net photosynthetic rate. Conversely, inhibited ethylene produce decreased endogenous ethylene release rate of wheat flag leaf, increased H2O2 production in flag leaf under waterlogged stress, induced stomata closed, aggravating net photosynthetic rate decrease. While under flowering waterlogging stress, high concentration of ethylene also increased H2O2 production in wheat flag leaf, resulted in Gs decline. It suggested that ethylene may influenced wheat flag leaf photosynthesis under waterlogged stress by regulating the stomatal opening mainly.3. Ethylene reduced wheat membrane lipid peroxidation damage raised by waterlogging stress. Compared with waterlogging treatment, exogenous ethylene improved flag leaf photosynthetic capacity under booting waterlogging stress by increasing soluble protein content of the flag leaf and sugar concentration in leaf cytoplasmic, decreased O2-production rate and MDA content, enhanced plant adversity resistance. Oppositely, under flowering stress, ethephon reduced POD activity, accelerated the aging of leaf. But inhibited ethylene produce decreased wheat flag leaf SOD activity, remained high free amino acid content in leaf under flowering waterlogging stress, impacted nitrogen accumulation and remobilization, lowered grain nitrogen accumulation.In conclusion, exogenous ethylene induced plant endogenous ethylene release, reduced the plant height under booting waterlogging stress, decreased flag leaf H2O2 content, relieved Gs decrease due to waterlogging stress, kept the stomata opened, moreover, held high soluble protein content of the flag leaf and sugar concentration in leaf cytoplasmic, increased flag leaf net photosynthetic rate, decreased O2- production rate and MDA content in cytoplasmic. Besides, after ACC pretreatment under waterlogging stress,1000-kernel weight added, grain yield improved, in flowering stage, exogenous ethylene increased grain nitrogen accumulation. Nevertheless, too high or too low endogenous ethylene content in plant may not only restrained stomatal opening, decreased antioxidase activity, sugar and free amino acid content changed abnormally, serious membrane lipid peroxidation, accelerated leaf and root senescence, reduced photosynthetic capacity, but also induced plant endogenous hormone imbalance, leading to yield reduction.