| Soil salinity is one of the major abiotic stress with adverse effects on plant productivity and quality. As the salt constantly accumulates in soil with irrigation, soil salinity becomes one of the greatest problems in agricultural production through out the world. Jatropha curcas L., as the first referent tree in the development of Chinese biological diesel oil and a hotspot of the research in the world facing global energycrisis recently, has a very high level of environmental adaptation. However, few studies have been reported on the mechanism of salt adaptation and chemical regulation of the tree. Improvement of salt tolerance to utilize extensive salt soil is an important issue in both agricultural and biological sciences. Moreover, salt tolerance improved by chemical regulation used to be considered as an economic and effective method. Paclobutrazol (PP333) causes metabolicand structural changes in plant, and improves plant stress tolerance.Therefore, in order to evaluate the effects of seed soaking in different concentrations of PP333on salt tolerance of J. curcas seedlings, the plant dry weight, root/shoot ratio, water content, the leaf cell ultrastructure, chlorophyll content, the photosynthesis, K+, Na+, Cl-contents (mmol·g-1DW), K+/Na+ratio and the percentage (%) of Na+, Mg2+, Cl-, K+and Ca2+contents in total inorganic ions of different tissues of J. curcas seedlings treated with200mmol·L-1NaCl for10d with previous seed soaking in different concentrations of PP3in greenhouse were investigated. The results obtained were as follows:(1)200mmol·L NaCl stress significantly decreased the seedling dry weight, water content and root/shoot ratio. However, compared with the plant treated only with NaCl, the plant dry weight. root/shoot ratio and water contents of the seedlings treated with seed soaking of PP333under NaCl stress were all increased significantly, and the effect of600mg·L-1PP333was optimal.(2) The photos of transmission electron microscope indicated that the leaf cells of J. curcas contained distinct starch grains, that elliptic chloroplasts clung closely to cell wall under control and that plasmolysis phenomenon and cell membrane damage of leaf cells under200mmol·L-1NaCl were obviously visible. Moreover, NaCl-treated chloroplasts did not contain starch grains but formed osmiophilic globules. However, in J. curcas seedlings treated with salt and with seed soaking in600mg·L-1of PP333, plasmolysis phenomenon did not occur, osmiophilic globule numbers decreased and osmiophilic globule volume diminished evidently.(3) Under the salt stress, with seed soaking in different concentrations of PP333, the Na+and Cl-contents of roots and leaves of seedlings were decreased, the K+contents and the K+/Na+ratio of roots and leaves of seedlings were increased.(4) Compared with control, in salt-treated J. curcas seedlings, chlorophyll content and net photosynthetic rate (Pn) were both decreased evidently. Compared with salt treatment, in the seedlings treated with salt and spraying in600mg·L-1of PP333, the chlorophyll content and net photosynthetic rate(Pn) were both increased significantly. To sum up, seed soaking in PP333could enhance the salt tolerance of J. curcas seedlings, and the effect of600mg·L-1PP333was optimal.In order to evaluate the effects of foliage spraying PP333on salt tolerance of J. curcas seedlings, the plant dry weight, root/shoot ratio, water content, the leaf cell ultrastructure, chlorophyll content, the photosynthesis, K+, Na+, Cl-contents (mmol·g-1DW), K+/Na+ratio, the percentage (%) of Na+,Mg2+, Cl-, K+and Ca2+contents in total inorganic ions of different tissues, the osmotic adjustment ability and the antioxidation ability of J. curcas seedlings treated with200mmol·L-1NaCl for10d with foliage spraying in600mg·L-1of PP333in greenhouse were investigated. The results obtained were as follows:(1)200mmol·L-1NaCl stress significantly decreased the seedling dry weight, water content and root/shoot ratio, and drastically increased the leaf electrolyte leakage. However, compared with the plant treated only with NaCl, the plant dry weight, root/shoot ratio and water contents of the seedlings treated with foliage spraying in600mg·L-1of PP333under NaCl stress were all increased significantly, and their leaf electrolyte leakage percentage was decreased significantly.(2) The photos of transmission electron microscope indicated that the leaf cells of J. curcas contained distinct starch grains, that elliptic chloroplasts clung closely to cell wall under control and that plasmolysis phenomenon and cell membrane damage of leaf cells under200mmol·L-1NaCl were obviously visible. Moreover NaCl-treated chloroplasts did not contain starch grains but formed osmiophilic globules However, in J. curcas seedlings treated with salt and with foliage spraying in600mg·L-1of PP333, the plasmolysis phenomenon did not occur, osmiophilic globule numbers decreased and osmiophilic globule volume diminished evidently,(3)J. curcas seedlings treated with200mmol·L-1NaCl showed weak osmotic adjustment ability (0.06MPa) in leaves. However, the seedlings treated with foliage spraying in600mg·L-1of PP333significantly displayed evident promotion in osmotic adjustment ability (0.49MPa in leaves of non-NaCl treatment and0.30MPa in leaves of NaCl treatment).(4)Under the salt stress, with seed soaking in different concentrations of PP333, the Na+and Cl-contents of seedlings were decreased,the K+, Ca2+and Mg2+contents of seedlings were increased.(5) Compared with control, in salt-treated J. curcas seedlings, chlorophyll content and net photosynthetic rate (Pn) were both decreased evidently. Compared with salt treatment, in the seedlings treated with salt and spraying in600mg·L-1of PP333, the chlorophyll content and net photosynthetic rate (Pn) were both increased significantly.(6) Compared with control, in salt-treated J. curcas seedlings, MDA content and POD activity were greatly enhanced, and SOD and CAT activities were decreased significantly. However, compared with salt treatment, in seedlings treated with salt and foliage spraying in600mg·L-1of PP333, MDA content and POD activity were significantly decreased, but SOD and CAT activities increased. To sum up, promotion of salt adaptation of J. curcas with foliage spraying in PP333was mainly attributed to the enhancement of the photosynthesis, the osmotic adjustment ability and the antioxidation ability. |
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