The effect of cytokinins benzylaminopurine (BAP) and thidiazuron on photosynthetic rate and enzyme activities in sugar beet, pea, meadow fescue and reed fescue leaves was studied. Low concentrations (3-10 g nr3) stimulated the net photosynthetic rate, the activities of ribulose-l,5-bisphosphate carboxylase/oxygenase (RuBPCO) and other enzymes of the carboxylation phase of Calvin cycle, i.e. ribose phosphate isomerase and phosphoribulokinase, and the cycle including the NADP-glyceraldehyde phosphate dehydrogenase complex. On the contrary, there was no change in phosphoenolpyruvate carboxylase activity. In treated leaves the quantity of RuBPC increased along with increases in the level of total leaf proteins. Thus cytokinins act, probably, by specific altering of the synthesis of certain proteins. Inducing or stimulating the synthesis of essential proteins involved in photosynthetic processes, cytokinins cause changes in photosynthetic activity.
The effect of abscisic acid (ABA) on the net photosynthetic rate the ribulose 1,5-bisphosphate carboxylase (RuBPC) and the phosphoenolpyruvate caiboxylase (PEPC) activities, the chlorophyll (Chl) content and growth of pea plants (Pisum sativum L.) grown under "white" (WR) or blue radiation (BR), were investigated. BR as compared to WR enhanced P^, the activities of examined enzymes, and Chl content. In špite of higher of the plants grown under BR, diy matter of their shoots was lower in comparison with WR. ABA-treated plants grown under both WR and BR showed reduction in Pn- ABA had no effect on the activities of both RuBPC and PEPC and the Chl content. Independent on the radiation quality, ABA reduced stem elongation, but did not affect the biomass of whole shoots.
Energy transfer from resynthesized protochlorophyllide (PChlide) to chlorophyll (Chl) appeared after 5 h irradiation and additional redarkening of etiolated barley leaves. The transfer was more effective after a longer greening. Benzyladenine (BA) removed delay at the onset of the energy transfer and this process was effective even at very low Chl contents. BA enhanced Chl accumulation more strongly than the development of photosystems. The balance between the rate of Chl synthesis and that of its efflux from PChlide-containing site may determine the number of Chl molecules near PChlide, and thereby the probability of the energy transfer. At a high rate of Chl synthesis a part of its molecules remained near the PChlide synthesis site. Under various conditions of irradiation the slower rate of Chl accumulation corresponded to the more efficient energy transfer. Chl accumulation at PChlide forming site probably Controls the activity of the multienzyme systém of Chl biosynthesis by a feedback mechanism. The BA addition increased the number of EF-mtramembrane particles and the munber of enzyme systems of Chl biosynthesis to the same extent.