Light-enhanced oil body mobilization in sunflower seedlings accompanies faster protease action on oleosins

Germination of sunflower (Helianthus annuus L.) seeds in light is accompanied by greater susceptibility of oil bodies for lipolytic action following enhanced oleosin mobilization than in the dark. The 16- and 17.5-kDa oleosins are mobilized within the first 4 d of seedling growth in light, whereas 20-kDa oleosin remains detectable. Oleosin mobilization is slower in the dark and all three oleosins remain detectable until 7 d of seedling growth. Light-grown seedlings show higher activity of fatty acyl-ester hydrolase (EC 3.1.1.1) mainly due to greater expression of its major (40–50 kDa) isoforms. Increased susceptibility of oil bodies to lipolytic action in light-grown seedlings shows a correlation with higher activity of a cytosolic 65-kDa protease, oleosin mobilization and relative accumulation of 11-kDa protease-protected fragment. These observations support the view that the expression of 65-kDa protease is enhanced in light and it could be considered as a component of light-enhanced lipolysis.