Leaf Senescence in a Stay-Green Rice Variety, SNU-SG1 and a Mutant, sgr

During leaf senescence, the most characteristic visible change is leaf yellowing due to the preferential breakdown of chlorophyll (Chl) with concomitant chloroplast degradation. In this study, we examined the characteristics for the staygreenness during dark-induced senescence (DIS) in two stay-green varieties, SNU-SG1 and sgr;. During DIS, Chl loss was delayed in SNU-SG1 and sgr; compared with that in wild type (WT), but the photochemical efficiency of PSII (Fv/Fm) was not. The content of the functional PSII during DIS, estimated as (1/Fo 1/Fm) was high in WT, but low in SNU-SG1 and sgr;. In both varieties, Fo parameter increased during DIS, indicating the detachment of LHCII in PSII. In western blot analysis, the D1 and LHCII of WT were detected even when leaves turned yellowed. However, D1 protein in sgr; completely disappeared after 2 days without significant decrease in LHCII. These results suggest that both of the SNU-SG1 variety and sgr; mutant are non-functional stay-green species and largely attributed to the high stability of LHCII with an early degradation of D1 protein as a key protein of PSII.