Effects Of Calcium Stress On Physiological And Cell Ultrastructural Features In 'Atago' And 'Kisui' Pear Seedling

Calcium is one of essential elements in plant, and plays very important actions on cell structure and physiological functions. As a signal transduction matter, calcium was extensively studied, while was rarely investigated as essential macroelement for pear growth. In this study, with sand culture,'atago'and'kisui'pear seedlings were selected as experimental materials, effects of different Ca treatments on concentrations of several mineral elements in different parts, photosynthesis characteristics and cell ultramicrostructure in leaves of two cultivars were determined and analysed. The main results were as follows:1. Effects of different Ca, such as 0,16,80, and 200 mg·L-1(80mg·L-1 was considered as control) on concentrations and distributions of Ca, K, Mg, Fe and Zn in different parts (such as leaf, stem of scion, rootstock and root) of 'atago' and 'kisui' plants were investigated with sand culture. The results showed that Ca concentrations in leaves of 'atago'and'kisui'were both higher than those of other parts, and with the increase of Ca concentrations, leaf Ca presented increasing trends. K concentrations in different parts of both cultivars could be ranked, from the highest to the lowest, as leaf, stem of scion, root and rootstock, and leaf K concentrations of both were relatively low under 200 mg·L-1 Ca treatment. Mg concentrations in leaves, stems of scion, rootstocks and roots of both cultivars were decreasing with the increase of Ca concentrations, no significant difference was found on leaf Mg between the two cultivars, while under 0,16mg·L-1 Ca treatments, Mg concentrations were significantly higher in stems of scion, rootstocks and roots from 'kisui'than from'atago'. Root Fe concentrations of both cultivars were the highest among different parts, and Fe concentration was significantly higher in roots from'atago'than from'kisui'. However, Zn concentration was significantly higher in roots from'kisui'than from'atago', and Zn in leaves and stems of scion from'atago'were relatively high. Thus, we thought that there exist obvious effects of Ca stress on concentrations and distribution of Ca, K, Mg, Fe, Zn in different part.2. Compared with the control(80mg·L-1Ca2+), the bimodal carves of net photosynthesis rate(Pn) were observed in 0,16,200 mg·L-1Ca2+ treatments on'atago', whereas on'kisui', unimodal curves of Pn were presented exception with Omg·L-1 Ca2+ treatment. Unimodal curves of transpiration rate(Tr) were found on'atago'beside Omg·L-1Ca2+, while Tr of 'kisui' presented bimodal carves in four Ca2+ treatments.3. Responses of cell ultrastructure of'atago'and'kisui'under Ca stress were similar. Compared with the normal Ca treatment, Ca stress induced that chloroplast shape changed, thylakoids lamellar structures, mitochondria envelope and nucleus were vague. Under 200mg·L-1 Ca treatment, chloroplast swelled, ratio of starch granules was relatively big, thylakoids lamellar structures were blurred, number of plastoglobuli decreased. Whereas under 16, Omg·L-1 Ca treatment, chloroplast changed to prolate, thylakoids lamellar structures were vague, ratio of starch granules was very small, number of plastoglobuli increased, especially under Omg·L-1 Ca treatment, chloroplasts of both cultivars were disintegrated.