| Acid rain pollution is one of the important ecological environment problems that domestic and foreign scholars have paid close attention to. Acid rain stress can directly or indirectly affect plant physiological processes, including photosynthesis. Chloroplast ATP synthase is the key enzyme in the process of energy conversion of photosynthesis. It provides ATP required by plant photosynthesis and the change in its activity could affect plant photosynthesis. In this study, the effects of acid rain on the growth and the function of chloroplast ATP synthase in rive leaves at different growth stages were investigated by using the methods of molecular biology, plant physiological and biochemical determination and the molecular dynamics, in which economic crops of rice(Oryza sativa) were used as experimental material using important, and acid rain was simulated based on its pollution. The main results are as follows:(1) Compared with the control, low-acidity acid rain treatment increased the leaf area, leaf fresh and dry weights, relative growth rate, and net photosynthetic rate in rice at different growth stages, and no damage symptoms of rice leaves were observed in this treatment. The above indices reduced at middle-acidity or high-acidity acid rain stress, and the change degrees increased as the acidity of acid rain increased, meanwhile, the damage symptoms of rice leave rose with increasing the acidity of acid rain. The change degrees of above indices varied at different growth stage. The change degree of rice leaf fresh(dry) weight in treatment group followed the order: tillering stage > seedling stage > booting stage > filling stage(fresh(dry) weight, acid rain at p H 4.5) tillering stage > booting stage > filling stage > seedling stage(fresh weight, acid rain at other p H values); booting stage > tillering stage > seedling stage > filling stage(dry weight, acid rain at other p H values). The main change order of net photosynthetic rate in rice was: tillering stage > filling stage > seedling stage > booting stage(acid rain at p H 4.5); booting stage > seedling stage > tillering stage > filling stage(acid rain at other p H values).(2) The low-acidity acid rain treatment increased the negative charges on the surface of ATP synthase proteins, and the UV absorption intensity, fluorescence emission intensity and negative peaks in CD spectroscopy of Tyr and Trp residues in ATPase molecule. Meanwhile, the contents of ordered secondary structure increased and the contents of disordered conformation decreased, increasing the stability of its secondary structure. The gene expression results show that the increase in the expression level of β-subunit resulted in the increase in the activity of Mg2+-ATPase, promoting photosynthetic phosphorylation activity and ATP content in rice leaves. The change degrees in above indices at different growth stages followed the order: filling stage > seedling stage > tillering stage > booting stage. The high-acidity acid rain treatment decreased the negative charges on the surface of ATP synthase proteins. The UV absorption intensity, fluorescence emission intensity and negative peaks in CD spectroscopy of Tyr and Trp residues of ATPase were also decreased. Meanwhile, the contents of ordered secondary conformation of ATPase decreased and the contents of disordered conformation increased, weakening the stability of its structure. The gene expression results show that the obvious inhibiting effect on ε-subunits caused the abnormal assembly of ATP synthase, and the decreases in the Mg2+-ATPase activity, photophosphorylation activity and the ATP content in rice leaves. The change degrees in above indices at different growth stages followed the order: booting stage > seedling stage > tillering stage > filling stage. Unlike Mg2+-ATPase activity, acid rain showed inhibiting effects on the Ca2+-ATPase activity at different growth stages, and the inhibiting degree followed the order: seedling stage > filling stage > booting stage > tillering stage. The microstructure of ATPase were changed after the ATPase treated with H, and the changes were more obvious with the increase in the number of H.(3) Under the low-acidity acid rain treatment, the intracellular concentration of H+ and Ca2+ in rice leaves increased, intracellular environment was acidified mildly, the leaf water content didn’t change, and water metabolism was still normal. Meanwhile, the absorption of the functional elements increased, causing an increase in the contents of some functional elements of chloroplast, and then the increase in the synthesis quantity and function of chloroplast ATP synthase. Under the high-acidity acid rain treatment, the intracellular concentration of H+ increased obviously, the intracellular Ca2+ concentration first increased and then dropped, the intracellular environment acidification became aggravating, and the leaf water content decreased, leading to the imbalance of water metabolism. Thus the absorption of the functional elements were affected, causing the decrease in the contents of functional elements in chloroplast. This reduced the synthesis quantity and inhibited the function of chloroplast ATP synthase. The main regular of the change degrees of above indices in rice leaves at different growth stages was: booting stage > seedling stage > tillering stage > filling stage(the intracellular concentration of H+ and Ca2+); booting stage > filling stage > tillering stage > seedling stage(leaf water content); booting stage > tillering stage > seedling stage > filling stage(functional element contents).In summary, low-acidity acid rain could enhance the activity and function of chloroplast ATP synthase by influencing the structure and increasing transcription of chloroplast ATP synthase, thus contributing to the improvement of the growth and photosynthesis of rice; Middle and high-acidity acid rain inhibited the activity and function of chloroplast ATP synthase by destroying its structure and reducing its transcription, and thus contributing to the inhibition of the growth and photosynthesis of rice. Booting stage was the most sensitive period of rice’s response to acid rain stress. These findings would provide a reference for environmental ecological effects of acid rain pollution, and provide an experimental and theoretical basis for scientifically evaluating the effects of acid rain on plants at different growth stages. |
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