Salinity Induces Granal Development in Bundle Sheath Chloroplasts of NADP-Malic Enzyme Type C4 Plants

Abstract

In NADP-malic enzyme (NADP-ME) type C4 plants, MC chloroplasts have well-developed grana, whereas BSC chloroplasts are generally characterized by highly reduced grana. In the previous study, salt treatment induced granal development in BSC chloroplasts of Zea mays, an NADP-ME type C4 plant. Therefore, we examined the effects of salinity stress on the granal structure of BSC chloroplasts in seven other C4 species belonging to the NADP-ME type. The plants were grown in soil and after a certain period of time, they were treated with 3% NaCl for 5 d. Ultrastructure and quantitative properties of chloroplasts at the middle part of leaf tissues were investigated. In BSC chloroplasts of all the C4 species, almost no structural damage was observed, but the development of granal stacking was induced under salinity condition. Granal indices and appressed thylakoid density of BSC chloroplasts in the salt-treated plants were higher than those in the control plants. In all the species, the structure of MC chloroplasts was more or less damaged by salt stress; thylakoids were swollen and chloroplast envelope was disorganized. These results suggest that the granal development in BSC chloroplasts and the high damage of MC chloroplasts are common features of NADP-ME type C4 plants under salinity stress.

Keywords

• Bundle sheath
• C4 plants
• Chloroplast
• Grana
• Mesophyll
• Salinity