Time courses of leaf content of cytochrome b6f complex and photosynthetic capacity after changes in growth irradiance
- Research School of Biology, The Australian National University, Australia.
- Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Japan.
- School of Life Science and Food Technology, Hanshan Normal University, PR China.
- Department of Life Sciences, Huizhou University, PR China.
- Xinjiang Production and Construction Group, Shihezi University, Shihezi, PR China.
- College of Life Sciences, South China Normal University, PR China.
The content of cytochrome b6f complex, a photosynthetic oxidoreductase between the two photosystems, is a major determinant of the leaf photosynthetic capacity. Although the effect of growth irradiance on the cytochrome content has been investigated intensively, the time course has been poorly characterized. Here, we evaluated the half-life of the cytochrome complex after transfer from high-light to low-light. Pea plants were cultivated in a growth chamber for 18 d under moderately-high light (HL; 360 μmol m-2 s-1) and then subjected to several treatments. When the plants were transferred to low-light (LL; 60 μmol m-2 s-1), the maximum photosynthetic O2 evolution rate (Pmax) of young fully expanded leaves exhibited an exponential decay for 12 d while that of control, leaves kept under HL, was constant. The decrease in Pmax appeared to result from a parallel decrease in the cytochrome content. These decreases were not suppressed by 1.5- and 5-h HL-exposure treatments in LL days. In addition, re-exposure to HL after 4-day LL did not increase the photosynthetic capacity, suggesting that the reduction of the photosynthetic capacity may be irreversible in mature leaves. Some recent results from experiments which attempt to suppress the reduction in leaf photosynthetic capacity will also be discussed.