Defects in a proteolytic step of light harvesting complex II in an Arabidopsis stay-green mutant, ore10, during dark-induced leaf senescence

During dark-induced leaf senescence (DIS), the non-functional stay-green mutant ore10 showed delayed chlorophyll (Chl) degradation and increased stability in its light-harvesting complex If (LHCII). These phenomena were closely related to the formation of aggregates that mainly consisted of terminal-truncated LHCII (Oh et al., 2003). The ore10 mutant apparently lacks the protease needed to degrade the truncated LHCII. In wild-type (WT) plants, protease was found in the thylakoid fraction, but not the soluble fraction. A similar experiment using dansylated LHCII revealed that the protease degraded both WT and ore10 LHCII, indicating that its stability in ore10 perhaps did not result from a defect in the LHCII polypeptides themselves. Although protease activity was not present in non-senesced WT leaves, it was induced during DIS. It also was possible to diminish the high level of protease present in the thylakoids through high-salt washing, suggesting that this enzyme is extrinsically bound to the outer surface of the stroma-exposed thylakoid regions.