Studies On Physiological Regulation Function Of Exogenous Proline On Melon Seedlings Tolerance To Salt Stress

Soil salinity severely affects the growth and development of crops and restricts their yields and quality. However, this phenomenon is becoming more and more serious because of special microclimate environment, high multiple crop index and unscientific management of water and fertilizer and needs to be solved urgently in greenhouse cultivation. Proline is a crucial osmotic adjustment in plants and will be accumulated to a higher lever when plants are in environmental stress, which plays an important role in enhancing resisting adversity of plants. In this paper, melon cultivars salt tolerance were identified and filtered. Based on the effects of exogenous proline on growth, photosynthesis, ROS metabolism, the absorption and distribution of mineral elements in melon cultivars (Cucumis melo L. cv. Yuhuang and cv. Xuemei) under100mmol·L-1salt stress, had studied the effects of exogenous proline on the nitrate reducation and proline metabolism in Xuemei, Main results were as follows:Salt tolerance of the12melon cultivars melon were compared by membership function method, and selected three high salt tolerant, six moderate salt tolerant and three sensitivity salt tolerant melon cultivars.Suitable concentration proline could alleviate damage caused by salt stress,0.1-0.4mmol·L-1proline could improve the fresh and dry weight of the melon seedlings under the salt stress remarkably and increase their chlorophyll contents as well as decreased H2O2content, O2-production rate, MDA content and membrane permeability. Among these results, the0.2mmol·L-1proline treatment showed the best effect. But the higher concentration of proline treatment1.6and3.2mmol·L-1made the damage on melon seedlings worse.Salt stress decreased SOD, CAT, DHAR, APX and GR activities of both melon cultivars, and the variation range of Xuemei was larger than Yuhuang. After using proline, the two cultivars’antioxidant activities and salt tolerance was increased while their O2·-production rate was decreased with H2O2content, MDA content and membrane permeability decreased as well under salt stress,and its effects on Xuemei was better than Yuhuang. exogenous proline also increased the content of non-enzymatic antioxidants such as ASA and GSH under salt stress and normal nutrient solution culture. Therefore, it showed that the exogenous proline can clear the ROS caused by salt stress by increasing the activities of antioxidant enzymed and non-enzymatic antioxidants content so that it can protect the membrane integrity to lessen the damage caused by the salt stress.Salt stress decreased the chlorophyll content, Pn and ΦPSⅡ, inhibited the growth, the effect was more markedly Xuemei than Yuhuang. Salt stress decreased Gs and Ci in cv. Yuhuang melon, increased Ci in cv. Xuemei. Exogenous proline increased chlorophyll content, Gs, Ci, ΦPS Ⅱ and qP in cv. Xuemei, increased Pn, Chlb and ΦPS Ⅱ in Yuhuang, Therefore, these results showed that exogenous proline can increase the actual photoche-mical efficiency to strengthen melons’salt tolerance by enhancing the transport rate of photo synthetic electron and light sharing distributed by photochemical reaction and its effects on Xuemei was better.Salt stress decreased ion contents, in creased the Na+and Cl-contents in melon, destroy the balance of mineral nutrient, the effect was more markedly Xuemei than Yuhuang; salt stress increased the N and P contents in roots, decreased in leaves. Exogenous proline markedly regulate the absorption to mineral nutrient under salt stress, increased N and P content in melon; and also Ca、K、Mg、Fe、Mo、Mn、Zn and Cu contents, enhanced K+/Na+、Mg2+/Na+and Ca2+/Na+ratio. These results showed that exogenous proline could alleviate the damage by accelerating melons’absorption of necessary nutrients, enhancing ion’s regional distribution ability and regulating the absorption balance of mineral nutrients.Salt stress increased NH4+-N, decreased NO3--N content, NR and GS activities in leaves and roots of cv. Xuemei melon, inhibit the absorption of nitrogen in melon; melon increased the salt torelent via to increase soluble protein and proline contents. Exogenous proline increased NR and GS activities, increased NO3--N, decreased NH4+-N content, promoting the absorption of N. exogenous proline improved the soluble protein and proline contents, feedback inhibite P5CS activity, increase OAT and ProDH activities. it could be concluded that the proline could regulate Nitrate reduction and foster their absorption to nitrogen to alleviate the damage caused by salt stress.melons salt tolerance could be improved by regulating their proline metabolism to increase the proline content.