Heat shock response of the chloroplast genome in Vigna sinensis

The light-dependent protein synthesis occurring in chloroplasts isolated from the leaves of 7-day-old Vigna sinensis responded to heat shock with the induction of a set of four heat shock proteins (HSPs). The synthesis of these four HSPs at the elevated temperature was transcriptionally regulated, and all of them were found to be thylakoid membrane-bound. The synthesis of these chloroplast-coded HSPs was also observed in etioplasts during protein synthesis at the elevated temperatures with the exogenously added ATP. The in vivo induction of these plastid-coded HSPs was observed only in the leaves subjected to gradual increase in temperature but not in leaves subjected to rapid heat shock. Further, the in vitro synthesis of these plastid-coded HSPs was seen only in chloroplasts isolated from the control or from leaves subjected to gradual increase in temperature and not in chloroplasts isolated from leaves subjected to rapid heat shock. Taken together these observations suggest that in V. sinensis, the plastid genome contains a definite heat shock response and the in vivo expression of this response corresponds to the gradual rise in temperature normally occurring under field conditions.