Localization and abundance of chloroplast protein synthesis elongation factor (EF-Tu) and heat stability of chloroplast stromal proteins in maize

摘要

Chloroplasts from a line of maize with high levels of chloroplast protein synthesis elongation factor (EF-Tu), ZPBL 1304, display greater heat stability than chloroplasts from a line with lower levels of EF-Tu, ZPL 389. We hypothesize that the greater heat stability of chloroplasts from ZPBL 1304 line may partly be attributed to EF-Tu, which may be protecting chloroplasts from heat injury. In this study, we investigated the subcellular distribution of EF-Tu and the heat stability of chloroplast stromal proteins in ZPBL 1304 and ZPL 389. Immunogold labeling and transmission electron microscopy (TEM) revealed that the chloroplast EF-Tu is localized mostly in the stroma and that under normal conditions agranal chloroplasts have a higher relative level of this protein than granal chloroplasts. Light scattering experiments with chloroplast stromal extracts showed that stromal proteins from the maize line with higher levels of EF-Tu, ZPBL 1304, display greater heat stability than stromal proteins from the line with lower levels of EF-Tu, ZPL 389. The results support the hypothesis that maize EF-Tu plays a role in the development of heat tolerance, possibly by acting as a molecular chaperone and protecting chloroplast stromal proteins from thermal aggregation