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Adaptive Responses of Birch-Leaved Pear (Pyrus betulaefolia) Seedlings to Salinity Stress

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One-year-old birch-leaved pear (Pyrus betulaefolia Bunge) seedlings were subjected to 0, 50, 100, 150, and 200 mmol/L NaCl solutions for 27 days in order to study the effects of salinity stress on photosynthesis, ion accumulation and enzymatic and non-enzymatic scavenging of reactive oxygen species in the seedlings. The research was performed in a greenhouse using potted trees. Salinity stress reduced photosynthetic rates, stomatal conductance and water use efficiency of leaves of the pear seedlings, but increased transpiration rates and leaf temperature. Hydrogen peroxide and superoxide anion radical contents increased with increasing NaCl concentrations, a phenomena also observed for malondialdehyde, suggesting that leaves of the pear seedlings suffered from oxidative injury. Superoxide dismutase (SOD) and catalase (CAT) activities quickly responded by increasing when the pear seedlings were subjected to salinity stress. Total protein content in leaves of the seedlings was restrained by salinity stress, whereas ascorbate content increased. Salinity stress reduced glutathione content once the birch-leaved pear seedlings were exposed to a low level (50 or 100 mmol/L) of NaCl, whereas a high level (150 or 200 mmol/L NaCl) of salinity stress stimulated the accumulation of glutathione. Salinity stress increased the accumulation of Na+, Cl-, K+ and Mg2+ in the seedlings, but reduced Ca2+ levels and the ratio of other ions to Na+ except K+/Na+ under 50 mmol/L NaCl conditions. This suggests that leaves of birch-leaved pear seedlings possess the capacity for salt exclusion only under 50 mmol/L NaCl conditions, and Ca2+ does not play a fundamental role as a secondary messenger under salinity stress conditions.


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