Differential effects of benzyladenine on the ultrastructure of chloroplasts in intact bean leaves according to their age

Abstract

Primary leaves of intact bean plants (Phaseolus vulgaris) were treated with benzyladenine (BA) at different stages of growth. Changes in the ultrastructure of chloroplasts and the contents of chlorophyll, carotenoid, and protein (soluble and insoluble) in leaves with different treatments were followed and compared. When BA was applied from an early stage, it increased the chloroplast size and the number of grana per chloroplast without any pronounced effect on the grana size. When BA treatment was stopped at the early stage, these effects remained for a while and then diminished. When BA treatment was begun at a late stage, such marked effects were not observed, suggesting that only young leaves could respond to BA in that manner. However, the late treatment efficiently prevented the process of the last stage of leaf senescence characterized by disintegration of thylakoids with concomitant increase in the plastoglobule size. Chlorophyll, carotenoid, and insoluble protein contents per leaf followed similar changes in chloroplast length and the number of grana per chloroplast section.