Photosynthetic apparatus in chilling-sensitive plants

Abstract

Changes in the levels of both ATP and protein in relation to Hill reaction activity following cold and dark storage and illumination of leaves of Lycopersicon esculentum Mill. were studied. Loss of Hill reaction activity observed during cold and dark storage of leaves for 3-4 days was accompanied by about 50% decrease of both ATP and protein levels while the content of chlorophyll was not affected Illumination of cold and dark stored leaves (8000 lx for 2 h) resulted in almost a complete restoration of both ATP and protein levels as well as Hill reaction activity. The latter process proceeded, however with different kinetics than the former ones. The rate of Hill reaction activity increase very rapidly from the beginning of illumination while the ATP level diminished during the first hour of illumination. In addition there was a lag in the increases in protein content. By about two hours of illumination all these processes reached the maximum values. Following illumination of leaf dises stored in the cold and dark in the presence of either cycloheximide or DCMU, both ATP and proteins levels as well as Hill reaction activity were greatly diminished. These data seem to suggest that the lack of reactivation of Hill reaction activity in the presence of these two inhibitors is due to inhibition of ATP synthesis required primarily for manganese reincorporation into the thylakoid membrane and theraby restoration of Hill reaction activity (Kaniuga, Zabek and Sochanowicz, Planta 1978b). Contribution of cytoplasmic protein synthesis in this process appears to be of secondary importance, although the inactivation and reactivation of electron transport are accompanied by a large loss (as high as 50%) and the restoration of the initial protein content in leaves following illumination.