EFFECT OF KINETIN ON ACTIVITY OF SOLUBLE AND MEMBRANE-BOUND RIBULOSE-1,5-BISPHOSPHATE CARBOXYLASE OF PEA-CHLOROPLASTS

We investigated direct (in vitro) and gene-mediated (in vivo) influenc e of kinetin on soluble rubisco (S-rubisco) and membrane-bound rubisco (M-rubisco) from pea leaves. Kinetin in a concentration ranging from 0.1 to 10 mg/liter did not affect activity of S-rubisco after direct a ddition to an unpurified enzyme preparation or a preparation purged of low-molecular-weight impurities on a column containing Sephadex G-75 from young, mature, and senescing leaves. Similarly, no effect was rec orded after introduction of kinetin (5 and 20 mg/h) to the incubation medium of isolated whole chloroplasts or at the time of infliction of osmotic damage to them. A positive effect of kinetin is detected for t he first time (in vivo) on activity of M-rubisco from intact chloropla sts isolated from leaves with recently completed active growth from se edlings preliminarily (5 days before) treated with a kinetin solution (20 mg/liter). Activity of S-rubisco also rose under the influence of kinetin, but by 40% less than that of M-rubisco. A change in the ratio of S-rubisco to M-rubisco activity was recorded in the test variant, and this apparently can play an important role in hormonal regulation of photosynthetic CO2 assimilation.