Changes in Levels of Thylakoid Components in Chloroplasts of Pine Needles of Different Ages

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Levels of thylakoid components in chloroplasts and transcripts of photosynthesis-related genes were compared in leaves of different ages, namely, current, 1-year-old and 2-year-old needles, of a Japanese black pine tree (Pinus thunbergii). Levels of thylakoid components, PSI, PSII and Cyt b_6/f complexes, measured as P700, Cyt b_<559> and Cyt f, respectively, were lowest in current needles, on a per needle basis, and were almost eight times higher in 1-year-old needles. Levels of PSI and Cyt b_6/f complexes were slightly lower in 2-year-old needles while the level of PSII remained unaltered or was even slightly higher than in l-year-old needles. The ratio of PSI to PSII decreased markedly as needles aged. By contrast, levels of cab, psaA/B, psbA, rbcS and rbcL transcripts were the highest in current needles, and the levels decreased with increasing age. The extent of the reduction was the greatest for psaA/B transcripts, with the level in 2-year-old needles being about 30% of that in current needles. The smallest reduction was observed in the level of psbA transcripts with about 90% of the current-year level in 2-year-old needles. These results suggest that PSII complex accumulates more slowly than PSI complex during leaf development, and that PSI and Cyt b_6/f complexes decay before PSII during the initial period of senescence.
日本植物生理学会の論文