Senescence-related changes in the subcomplex arrangement of the major light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) as influenced by cytokinin

Abstract

The major light-harvesting chlorophyll a/b-protein complex of photosystem II (LHCII) from fresh barley leaves could be resolved by non- denaturing IEF into five trimeric subcomplexes designated 1-5 in order of decreasing pI value. IEF-based analysis of PSII particles isolated from leaves in which the processes of senescence were induced by detachment and dark-incubation in the presence of water for 0-8 days let us reveal that substantial rearrangements of LHCII organization took place throughout the course of senescence comprising a step-wise decline in relative abundance of subcomplexes 1-3 (down to 0-58% of the initial abundance during 8 days of aging) and an increase in the relative abundance of the subcomplexes 4 and 5. Using SDS-PAGE and immunoblot analysis it was shown that the rearrangements were linked to the in the relative levels of LHCII apoproteins i.e. 26.7 and 25.6 kDa ones. The changes comprised the preferential disappearance of the 26.7 kDa polypeptide and an enrichment of 25.6 kDa one and most probably reflect the heterogeneity among LHCII apoproteins concerning their stability under the conditions of chl loss. Kinetin was able to repress the senescence- related rearrangements in LHCII subcomplex organization at late stages of aging (5-8 days) by preventing over this time period the disappearance of 26.7 kDa polypeptide and the enrichment of 25.6 kDa one.