DIURNAL AND CIRCADIAN LIGHT-HARVESTING COMPLEX AND QUINONE B-BINDING PROTEIN-SYNTHESIS IN LEAVES OF TOMATO (LYCOPERSICON-ESCULENTUM)

In leaves of tomato (Lycopersicon esculentum), the synthesis of a light-harvesting complex (LHC) polypeptide of photosystem II and the quinone B (Q(B))-binding protein varies at different time points during the day. In vivo labeling with [S-35]methionine revealed diurnal oscillations of synthesis of these thylakoid membrane proteins. Both proteins are synthesized at elevated levels right after the transition from darkness to light, a maximum is reached around noon, and decreasing levels were measured during the afternoon and night. In addition, in constant darkness both proteins were also synthesized to varied extents at different diurnal time points. Together, these results indicate that the synthesis of a LHC II and the Q(B)-binding protein is under the control of the circadian clock. This circadian oscillation of LHC II protein synthesis correlates with the very well documented circadian Lhc a/b mRNA accumulation.