Abstract: 【Objective】The changes of cell structures and physiological characteristics in leaves and stems of two Gossypium barbadense varieties, Yuehai 9 (salt tolerance) and PS-7 (salt sensitive), were investigated under different salt stress conditions. Morphological and physiological mechanism of salt tolerance in Gossypium barbadense to salt stress at seedling stage was studied to offer a theoretical basis and technical reference for selecting salt-tolerant genes in cotton cultivars. 【Method】In a water culture experiment, three-leaf cotton seedlings were treated with NaCl at 300 mmol·L^-1 NaCl for different times. This study involved observation of morphological features and comparison of physiological indexes of two Gossypium barbadense, Yuehai 9 (salt tolerance) and PS-7 (salt sensitive) under different salt stress treatments by means of optical microscopy and measurement of physiological indices.【Result】There was a difference in effect on two cotton cultivars by salt stress. At 300 mmol·L^-1 of NaCl, with the prolongation of treatment period, the transections of the leaves and stems of Yuehai 9 and PS-7 were both significantly smaller compared with the control groups, decreased, respectively, by 14.10%, 54.69% and 45.30%, 87.90% at 300 mmol·L^-1 of NaCl after 24 h, and the variation range of PS-7 was larger than that of Yuehai 9. The xylem of the vascular bundle of PS-7 was severely damaged while the xylem of the vascular bundle of Yuehai 9 showed no significant change in 300 mmol·L^-1 of NaCl treatment for 12 h. The long cylindrical palisade tissue cell of PS-7 became smaller and ovoid in 300 mmol·L^-1 of NaCl treatment after 24 h while the shape of the palisade tissue cell of Yuehai 9 showed no change. The chlorophyll contents, superoxide dismutase and peroxidase activities in leaves of Yuehai 9 were significantly higher than those of PS-7, while its malondialdehyde contents was lower than that of PS-7. Yuehai 9 and PS-7 were different in chlorophyll contents, malondialdehyde contents, superoxide dismutase and peroxidase activities, and the differences reached a significant level at 300 mmol·L^-1 of NaCl after 8 h. 【Conclusion】 The most sensitive plant part to salt stress may be the palisade tissues of leaves and xylem in the stem. The chlorophyll, malondialdehyde, superoxide dismutase and peroxidase can be used as the physiological indexes for evaluating and selecting salt tolerance cotton materials.

Key words: Gossypium barbadense L., seedling, salt stress, morphological index, physiological index