Studies Of Salicylic Acid On Senescence And Net Photosynthetic Rate Of Leaves In Three Pears

Whangkeumbae,Yali and Huangguan pear were used as the experiment material with different concentrations of SA solution.( using Oretool/L,0.05mmol/L,0.Smmol/L,5mmol/L SA sprayed pears leaves; using 0retool/L,0.002mmol/L,0.02retool/L,0.2mmol/LSA cultured leaf discs ) The changes of physiologic indexs had been studied as leaf senescence, the effects of SA on net photosynthetic rate and microstructure of three cultivars had also been researched, the results showed the effects of exogenous salicylic acid on senescence,net photosynthetic rate of pear leaves. Furthormore, the changes of physiologic metabolism, together with the leaves microstructure, revealed the mechanism of SA on regulating the senescence,net photosynthetic rate of pear leaves. It will provide theoretical basis for delaying the leaves senescence,improving net photosynthetic rate,promoting early fruits. The main results were as follows:1. Different concentrations of SA solution could alleviate the degradation of the nutrient of senescent leaves. 0.5mmol/L SA had the apparent effect on cutting down the degradation of chlorophyll of Whangkeumbae andYali leaves, 0.05 mmol/L SA had dramatic effect on Huangguan leaves; 5 mmol/L SA could obviously control the protein content of Whangkeumbae and Yali leaevs, 0.5 mmol/L and 5 mmol/L SA had highly significant on Huangguan leaves.2. Different concentrations of SA solution could keep high activity of antioxidases of senescent leaves. 0.5 mmol/L SA was the best treatment on decreasing the reduction of SOD activity, especially, the effects on Huangguan and Yali leaves had been dramatically significant; 0.5 mmol/L SA obviously controlled the reduction of POD activity, the effect on Yali leaves had been extremely significant.3. Different concentrations of SA solution could protect cell membrane of senescent leaves. 0.5 mmol/L SA could obviously reduce the increase of relative conductivity rate on Whangkeumbae leaves, the effect of 5rnmol/L SA was extremely obvious on Yali and Huangguan leaves; 0.5 mmol/LSA had the best effect on reducing the increase of MDA content of these three cultivars.4. Treating leaf discs of three pears with different concentrations (0.002 mmol/L -0.2 mmol/L) of SA solution could delay the leaves senescence at different degrees. 0.2 mmol/L SA had the prominent effect on elevating the chlorophyll and protein content, enhancing the activity of SOD,POD, reducing the conductivity,MDA content.5. Different concentrations of SA solution had the apparent impact on keeping cell integrity,improving the volume and amount of chloroplast. 0.5mmol/L SA was the optimal treatment.6. Different concentrations of SA solution could increase the net photosynthetic rate of Huangguan leaves. Pn had been obviously improved 42.57% as compared to without-treatment after four hours by 0.5 mmol/L SA treatment, and this treatment had the highest Pn after four days with 99.23% as compared to without-treatment.