| Poly y-glutamic acid (y-PGA) which is produced by microbial fermentation is a high polymeric substance carried biological activity. At present, its effects on enhancing the growth of crops are found, however, the physiological mechanism in plants'resistance has not known yet. Meanwhile, drought, salinity and chilling stress are the main abiotic factors threating crops'growth and production. The present investigation focused on the effects of exogenous y-PGA on the growth and physiological changes of hybrid rice under drought, salinity, chilling stress through solution culture method, the alleviation effects and physiology mechanism were explored. The details are as follow:1. Effects of y-PGA on the growth and osmotic adjustment of hybrid rice Jinyou 38 under the polyethylene glycol 6000 (PEG-6000) simulated drought stress in a hydroponics culture were investigated. When 100 and 200 mg·L-1 exogenous y-PGA were applied respectively under the stress of 12.5% PEG-6000, the withering rates of rice seedlings were decreased, the leaf fresh weights and the leaf vigor activities were obviously improved. The reactive oxygen species accumulation were strongly reduced when 100 and 200 mg·L-1 exogenous y-PGA were applied, the contents of organic osmotic substances, such as proline, free amino acids and soluble sugar were rising compared with control, ranges of the rise were 1.32%-8.62%,2.29% 10.71%,13.01%-28.57%, respectively. Also, the decrease rates in potassium ions were alleviated apparently compared with the control under the drought stress (P< 0.05).2. Effects of exogenously applied y-PGA on rice seedlings under 150 mmol·L-1 NaCl stress were investigated. Our research shows that salt stress caused a significant inhibition of seedlings'growth, while we found exogenous y-PGA effectively mitigated it, and we selected 100 mg·L-1γ-PGA from the concentration testing to do the further experiments. The benefit of applying exogenous y-PGA was found in three aspects:first, it increased the antioxidant enzymes and decreased the level of oxidative damage. Second, the seedlings applied by exogenousγ-PGA accumulated less Na+ content and maintained a better equilibrium ratio of Na+/K+. Furthermore, exogenous y-PGA induced an abundant accumulation of some osmoregulation substances such as proline, free amino acids and soluble sugar, these substances remained higher levels than that of only 150 mmol·L-1 NaCl stress treatment in 4 d. To our knowledge, this is the first report aboutγ-PGA application in rice salt stress improvements. It suggests that exogenous 100 mg·L-1 exogenous y-PGA improved the salt resistance of rice seedlings by the mitigation of oxidative damage, ions toxics and osmotic stress.3. Rice seeds were treated with y-PGA during germination period for 7 d, then removed exogenousγ-PGA and the seeds were exposed to chilling stress for 2 d. Under this method, effects ofγ-PGA on rice seeds germination and seedlings'chilling stress were investigated. The result shows:compared with the control of no y-PGA treatment, rice roots, shoots fresh and dry weight were improved when 100 mg·L-1 exogenousγ-PGA treated 7d, transport efficiency of storage substance and total amylase activity of seeds increased 31.81%,16.33%, respectively. In the following chilling stress, seedlings which treated by y-PGA exhibited better resistance, the concrete features were:under chilling stress, the loss of weight of roots and shoots was alleviated, survival rates were higher, roots kept stronger activity, and root tips accumulated less ROS. These indicated thatγ-PGA could strengthen rice seed germination, made seedlings more robust, and enhanced rice resistance.To sum up, exogenousγ-PGA contributed a lot to the alleviation of drought, salinity, cold stress of rice. It could indirectly regulate the lever of some physiology and biochemistry substances under abiotic stress, so that improved seedlings'resistance. |
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