EFFECTS OF 5-AMINOLEVULINIC ACID ON THE ACCUMULATION OF CHLOROPHYLL-B AND APOPROTEINS OF THE LIGHT-HARVESTING CHLOROPHYLL A/B-PROTEIN COMPLEX OF PHOTOSYSTEM-II

The effects were examined of 5-aminolevulinic acid (ALA) on the accumulation of Chl and apoproteins of light-harvesting Ch1 a/b-protein complex of photosystem II (LHCII) in cucumber cotyledons under intermittent light. A supply of ALA preferentially increased the accumulation of Ch1 a during intermittent illumination. However, when cotyledons were pretreated with a brief exposure to light or benzyladenine (BA), the stimulatory effect of ALA on the increase in the level of Ch1 b was greater than that in the level of Ch1 a, resulting in decreased ratios of Ch1 a/b. Time-course experiments with preilluminated cotyledons revealed that LHCII apoproteins accumulated rapidly within the first 30 min of intermittent illumination with a decline during subsequent incubation in darkness. A supply of ALA did not affect the accumulation of LHCII apoproteins during the intermittent light period, but it efficiently inhibited the decline in their levels during the subsequent darkness. After exposure to a single pulse of light of BA-treated cotyledons, the prompt increase in levels of LHCII apoproteins was not accompanied by the formation of Ch1 b, which began to accumulate later. The pattern of changes in levels of LHCII apoproteins was quite similar to that in levels of Ch1 a. These results suggest that LHCII apoproteins are first stabilized by binding with Ch1 a and that an increased supply of Chl a and the accumulation of LHCII apoproteins are prerequisites for the formation of Ch1 b.