Influence of natural saline-alkali stress on chlorophyll content and chloroplast ultrastructure of two contrasting rice (Oryza sativa L. japonica) cultivars

This study examined the changes of chlorophyll content and chloroplast ultrastructure in mesophyll cells of two rice (Oryza sativa L. spp. japonica) cultivars with different saline-alkali tolerance (Suijing NO.5: salinity-alkalinity-tolerant, and Songjing NO.6: salinityalkalinity-sensitive). Both rice cultivars were grown under three natural occurring saline-alkali conditions, as well as the normal condition as control. All types of soils were obtained from Zhaodong city Heilongjiang province in their natural forms. The chlorophyll content of both rice cultivars was significantly higher than control under mild saline-alkali stress, and the chloroplasts showed no significant structural distortion. In contrast, the content of chlorophyll was significantly reduced in two cultivars and the chloroplasts swelled under moderate and severe saline-alkali stress, compared to the control. The grana lamellae of the chloroplasts were distorted and the chloroplast membrane suffered different degrees of disintegration. When the stress intensified, the chlorophyll content of Songjing NO.6 decreased from 2.671mg/g FW to 3.57mg/g FW and the chlorophyll content of Suijing NO.5 decreased from 3.456mg/g FW to 4.105mg/g FW. The chloroplast ultrastructure appeared to be severely destroyed in both cultivars. However, cultivar Suijing NO.5 exhibited less decrease in the chlorophyll contents and less damage in the chloroplasts ultrastructure than Songjing NO.6, which is consistent with the known difference in the salinity-alkalinity tolerance of the two rice cultivars.