| Pingshan pomelo (citrus grandis Osbeck>> and Guanxi pomelo were used as materials in the experiment. Effects of NaCl stress on seed germination, the growth of seedlings, mineral elements absorption, cytoultrastructure of leaves and roots, contents of endogenous hormones and endogenous polyamines, contents and components of protein, photosynthesis, chlorophyll a fluorescence induction kinetics and changes in physiological characteristics were studied. The main results were as follows: 1 Effects of NaCI stress on seedling growth and ion absorption characteristics of pomelo1.1 Seed germination percentage and seedling growth of Pingshan pomelo were not affected when the treated concentration of NaCl up to 40mmoL"1, but the time needed to complete germination was lengthened. NaCl concentration higher than 60mmoL~1 decreased final germination percentage, inhibited the growth of radicle and sprout, the inhibition was strengthened along with the increasing of NaCl concentration, Germination percentage of Pingshan pomelo was higher than Fuju and the inhibited extent of radicle sprout , and the inhibition was strengthened , along with the increasing of NaCl concentration. Germination percentage of Pingshan pomelo was higher than Fuju and the inhibited extent of radicle and sprout was lower than Fuju under the same NaCl concentration.1.2 The changes in celluar ultrastructure of leaves and roots of Pingshan pomelo were significant at NaCl concentration up to SOmnioLT1, the cell deformed severely, plasmolysis distinctly and the structure of organelle was destroyed or even collapsed when NaCl concentration was higher than SOmmoL"1. At the same time, NaCl salinity decreased drastically seedling plant height, leaf area, shoot dry weight and root dry weight of Pingshan pomelo, the decrements were higher in Fuju than in Pingshan pomelo.1.3 As NaCl concentration increased, Na and Cl contents in both root and the above ground parts of Pingshan pomelo seedlings were remarkably increased, but they are lower than the contents of Na and Cl in Fuju seedling, This was related to smaller Na+and Cl~ absorption amount and absorption rate with lower affinity of Pingshan pomelo seedlings. So the salt tolerance of Pignshan pomelo was stronger than Fuju. NaCl salinity decreased contents of K^ Ca%Mg, P and Mn in both root and the above ground parts of Pingshan pomelo,96the contents of Fe -, Zn and Cu varied with organ. In addition, the value of K/T^^ Ca/Na and Mg/Na reduced remarkably with increasing NaCl salinity. the values of K/Nax Ca/Na and Mg/Na were higher in Pingshan pomelo than in Fuju under the same NaCl concentration.1 .4 NaCl salinity was showed to result in the increase of glycinebetaine contentin seedling shoots and roots of Pingshan pomelo, which was good at adaptation to NaCl stress.2 Effects of NaCl stress on endogenous hormones N endogenous polyamines and content and component of protein in leaves of pomelo2.1 Under NaCl stress, the contents of endogenous IAA,GAs and CTK in seedling leaves of Pingshan pomelo decreased, whereas the content of ABA and the ratios of ABA/IAA, ABA/GA3 , ABA/CTK and ABA/( lAA+GAs+CTK ) increased, which the ABA content, the ratios of ABA/GAs and ABA/CTK were closely related to salt tolerance. The content of ABA and the ratios above were higher in Pingshan leaves than in Fuju.2.2 The contents of endogenous Pu^ Spd and Spm and the ratios of Put /Spd* Put/Spm increased under 80mmol/L~1NaCl stress. The increasing ranges of total polyamines ^ Put> Spd and Spm as well as the ratios of Put/Spd and Put/Spm in Pingshan pomelo were much than those in Fuju. therefore, the increment in Put content and in ratios of Put/Spd and Put/Spm were an adaptive response of Pingshan pomelo to NaCl stress.2.3 The composition of some proteins were obstructed and some new proteins were induced under NaCl stress. 80^67^54^32^28^ 18^ 16 kilodaltons proteins exhibited unchangeable and expressed stably, 35 and 24 kD were prese...
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