LEAF DEVELOPMENT IN LOLIUM-TEMULENTUM - PHOTOSYNTHESIS AND PHOTOSYNTHETIC PROTEINS IN LEAVES SENESCING UNDER DIFFERENT IRRADIANCES

Changes in carbon fixation rate and the levels of photosynthetic prote ins were measured in fourth leaves of Lolium temulentum grown until fu ll expansion at 360 mumol quanta m-2 s-1 and subsequently at the same irradiance or shaded to 90 mumol m-2 s-1. Ribulose-1,5-bisphosphate ca rboxylase/oxygenase (Rubisco), light-harvesting chlorophyll alb protei n of photosystem II (LHCII), 65 kDa protein of photosystem I (PSI), cy tochrome f (Cyt f) and coupling factor 1 (CF1) declined steadily in am ount throughout senescence in unshaded leaves. In shaded leaves, howev er, the decrease in LHCII and the 65 kDa protein was delayed until lat er in senescence whereas the amount of Cyt f protein decreased rapidly following transfer to shade and was lower than that of unshaded leave s at the early and middle stages of senescence. Decreases in the Rubis co and CF1 of shaded leaves occurred at slightly reduced rates compare d with unshaded leaves. These results indicate that chloroplast protei ns in fully-expanded leaves are controlled individually, in a directio n appropriate to acclimate photosynthesis to a given irradiance during senescence.