Effects Of Exogenous Polypeptides On ’Brazil’ Banana Seedlings In Physiological Characteristics Under NaCl Stress

In this paper,’Brazil’banana(Musa AAA Cavendish subgroup cv.Brazil)were grown to study the effects of exogenous polypeptide on growth, photosynthetic, antioxidative system and ion distribution under NaCl(150 mmol·L-1) stress. The objective was to clarify the possible physiological and biochemical mechanisms of polypeptide on alleviating salt stress in banana. The main results are summarized as follows:1. Under 150 mmol·L-1 NaCl stress condition, the effects of polypeptide at the concentrations of (400,600,800,1000 times) on physiological characteristics of ’Brazil’seedlings were investigated. The results showed that growth of’Brazil’ seedlings were limited under NaCl stress.600,800 and 1000 times polypeptide treatments could increase ’Brazil’seedlings fresh weight,dry weight and relative water content; 400 times treatment limiting the’Brazil’banana growth.2. Under 150 mmol·L-1 NaCl stress condition,’Brazil’with the extension of time dealing with stress the roots activity in decline, The 600,800,1000 times polypeptide can further improve the’Brazil’plants roots activity and remain the high concentration.3. Under 150 mmol·L-1 NaCl stress condition, the’Brazil’stimulate the infiltration of regulatory function, expressed as proline, total soluble sugar and soluble protein content of the material conditions of infiltration in the early treatment significantly increased, but with the extension of time dealing with stress, the osmolyte in decline, so that’Brazil’salt injury suffered heavier. The 600,800,1000 times polypeptide can further improve the’Brazil’plants osmolyte and remain the high concentration.4. Under 150 mmol·L-1 NaCl stress condition, decreased the chlorophyll content, photosynthetic rate and the photochemical efficiency. Exogenous polypeptide 600,800,1000 times treatment increased photosynthetic rate(Pn),practical photochemical efficiency (OPSⅡ).5. Under NaCl stress, a serious impact on the activity of’Brazil’ plants oxygen system, the promotion of the lipid peroxidation. The peroxidase (POD) increased after the first lower, catalase (CAT) and superoxide dismutase (SOD) activity declineded. The content of malondialdehyde (MDA) and membrane permeability increased. NaCl stress can stimulate the’Brazil’o active oxygen scavenging system enzyme system in the SOD, POD, such as enzyme activity, but with the extension of the time, NaCl stress intensifies, active oxygen scavenging system in the activity of decline. Exogenous polypeptide can reduce the accumulation of leaves MDA and membrane permeability, effectively alleviate stress caused by salt’Brazil’ leaf cells of lipid peroxidation. Effects of 600-1000 times exogenous polypeptide, significantly increased tomato leaves POD, CAT, SOD activity, and be able to guarantee its long period of time to maintain high activity, thus reducing the content of the MDA, to maintain the stability of the film, Increase the salt tolerance of’Brazil’.6. Under 150 mmol·L-1 NaCl stress condition,contents of Na+ in leaf, psedostem and root of’Brazil’were increased while the ratios of ’Brazil’K+/Na+ were in hibited. With prolonging of treatment time, content of Na+ in banana was increased while the K+ content and ratios of wheat K+/Na+ were declined. Polypeptide treatment has not higher K+ and lower Na+ contents, but by increasing lower of Na+, higher increased extents K+ and decreased extents of K+/Na+, salt resistant decreased ion stress to CK. Compared with same plants,root had more higher content of Na+、and lower K+content,ratio of K+/Na+.7. From the results can be seen, the different concentrations of exogenouspoly peptideimproved the physiological and biochemical indicators. The adopt consistence is 600 times, but when the consistence of salicylic acid raise too high the effect of relieve is not obvious. The mechanism and molecular basis are not very clear, so exogenous polypeptide improve the mechanism of resistance still needs further study.