Ultrastructural And Physiological Responses,and StSnRK2 Gene Expression Of Potato(solanum Tuberosum L.) Plantlets To Osmotic Stress

Salinity and drought are the major abiotic stresses that impact plant growth and reduces the productivity of field crops. Compared to field plants, in vitro plantlets offer a direct and fast approach to investigate the mechanism of salt and drought tolerance. Here we examined the ultrastructural alteration, physiological responses and St Sn RK2 gene expresion of potato(Solanum tuberosum L. c.v. ‘Longshu No. 3’) plantlets to gradient saline stress(0, 25, 50, 100 and 200 m M Na Cl) and gradient water stress(0, 2%, 4%, 6% and 8% PEG) respectively,with three continuous observations(two,four and six weeks, respectively). The results showed that:1. with the increase of external Na Cl concentration and the duration of treatments,(1) the number of chloroplastsand and cell intercellular spaces markedly decreased;(2) cell walls were thickened and even ruptured;(3) numerous vesicles;(4) mesophyll cells and chloroplasts were gradually damaged to a complete disorganization containing more starch;(5) Na and Cl relative content increased and were mainly distributed in leaves;(6) K content decreas markedly and were mainly distributed in roots;(7) leaf proline content and the activities of catalase(CAT) and superoxide dismutase(SOD) increased significantly;(8) leaf malondialdehyde(MDA) content increased significantly, stomatal area and chlorophyll content declined. Severe salt stress(200m M Na Cl) inhibited plantlet growth. These results indicated that potato plantlets adapt to salt stress to some extent through accumulating osmoprotectants, such as proline, increasing the activities of antioxidant enzymes, such as CAT and SOD, and structure changes, such as vesicles and thickened cell wall.2. with the increase of external PEG concentration and the duration of treatments,(1) cell intercellular spaces markedly decreased and cell walls were thickened;(2) the number of chloroplastsand increased significantly;(3) there were some secondary vacuole in cytoplasm;(4)plastoglobuli markedly increased;(5) the number of starch grains markedly increased and volume were much larger;(6) cell was filled with starch separated from chloroplast, and chloroplast degraded into stripe;(7) leaf proline content and the activities of catalase(CAT) and superoxide dismutase(SOD) increased significantly;(5) leaf malondialdehyde(MDA) content increased significantly, chlorophyll content decreased. Severe drought stress(8% PEG) inhibitedplantlet growth. In the early low drought stress, through physiological and ultrastructural responses, potato plantlets adapt to drought conditions to some extent.3. Potato St Sn RK2 gene expression modes under salt and drought stress were different,(1)relative expression levels of different treatment at the same time was obvious different;(2)relative expression levels under different time at the same treatment also had difference;(3)expression trend under different stress was different, especially St Sn RK2.5, which expression levels after salt stress were lower than contrast; expression levels after drought stress were higher than contrast;(4) The different correlation was observed between the expression of St Sn RK2 and some physiological characteristics.