Changes in chloroplast ultrastructure, fatty acid components of thylakoid membrane and chlorophyll a fluorescence transient in flag leaves of a super-high-yield hybrid rice and its parents during the reproductive stage

In plants, it is well established that chloroplast is one of the early targgeted organelles to breakdown during leaves senescing. Here we applied a newly developed super-high-yield hybrid rice (Oryza sativa) LiangYouPeiJiu (LYPJ) and its parents lines to investigate changes in ultrastructure of chloroplasts, fatty acid composition of thylakoid membrane lipids and chlorophyll (Chl) a fluorescence transient in natural senescing leaves. We found that at full expansion of flag leaves in three lines, chloroplasts often showed oblong shapes with a typical membrane system of stroma and grana thylakoids, whereas their shapes had been changed from oblong to spherical during senescence. Our data showed that the initiation of senescence displayed accumulation of starch and an increase in the number and size of plastoglobuli with the damaged thylakoid membranes; subsequently, swollen thylakoid membranes in stroma and in grana with a significant increase in MDA content, and disorganization of thylakoid membrane system with significant changes in fatty acid composition of thylakoid membrane lipids were developed. Compared with its parents, the newly developed hybrid rice LYPJ had the highest capacity of carbohydrate transport from leaves (sources) to ears (sink), marked with the lowest accumulation of starch grains in the leaf chloroplasts, and the slowest senescing rate of chloroplast in overall leaf senescence process. Chl a fluorescence transients of three kinds of flag leaves were analyzed by so-called JIP-test. The results of analysis suggest that these findings inculding a high inherited activity of antioxidant enzymes and high photosynthetate transport to pretect chloroplast structure in the hybrid rice LYPJ have close relations to its super-high yield.