EFFECT OF BENZYLADENINE ON DIURNAL CHANGES IN DNA CONTENT PER CHLOROPLAST AND CHLOROPLAST REPLICATION IN INTACT BEAN-LEAVES

The effect of benzyladenine (BA) on the diurnal changes in DNA and Chl contents per chloroplast and chloroplast replication in primary leaves of bean plants (Phaseolus vulgaris L.) grown under a 16 h light/8 h dark cycle was studied. Experiments were made on primary leaves in the early expansion phase, where cell division had been completed but chloroplasts were replicating. In untreated controls, chloroplast number, Chl content and fresh weight per leaf showed daily periodic changes. Chl content per chloroplast increased in the light period every day, and fresh weight per leaf increased most rapidly in the early dark period. Chloroplast number per leaf increased rapidly in the early dark period on day 9, though the increase began a little earlier and was less sharp on days 8 and 10. During these periods, DNA content per chloroplast was decreasing due to chloroplast division as chloroplast DNA (ctDNA) per leaf remained unchanged throughout the experimental period. BA induced increases in Chl content per chloroplast, ctDNA content and fresh weight per leaf within 6 h of its application, regardless of whether it was applied at or 10 h after the beginning of the light period. Application of BA at 10 h in the light period shifted the start of chloroplast replication by 6 h compared to that in untreated controls. However, when BA was applied at the beginning of illumination, the start of chloroplast replication showed the same relative change in time as above. 5-Fluorodeoxyuridine (5-FdU) promptly prevented BA-induced increase in Chl content and chloroplast number per leaf as well as ctDNA content per leaf.