Decrease of Photosystem II Photochemistry in Arabidopsis ppt1 Mutant Is Dependent on Leaf Age

In the present study, we compared the effect of leaf age at one development stage on the photosynthetic behavior of a T-DNA-tagged allele of the ppt1 mutant. Chlorophyll fluorescence (Fv/Fm, where Fm is the maximum fluorescence yield and Fv is variable fluorescence) and fluorescence decay kinetics of the ppt1 mutant were different in leaves of different ages. The steady state levels of thylakoid membrane proteins in 40-day-old leaves were decreased compared with those in 20-day-old leaves and changes in photosystem (PS) II proteins were correlated with those of the Fv/Fm ratio in the ppt1 mutant. Increased accumulation of leaf sugars was accompanied by decreased photosynthetic gene transcripts and protein content in 40day-old leaves of the mutant. Thus, the results of the present study provide evidence for the phosphate translocator in maintaining normal photosynthesis at a late leaf age.