Activities of crucial enzymes involved in the Calvin cycle, glycolysis, and oxidative pentose phosphate cycle (PPC) were investigated in green calli of sugar beet {Beta vulgaris L.) during the transitíon from photoheterotrophic to photoautotrophic growth. The actívities of the Calvin cycle enzymes were increased by lowering the sucrose concentration of the medium, whereas the actívities of dissimilatíon related enzymes were either decreased or not inftuenced. The photoautotrophic culture cultívated on sucrose-free medium and 2 % CO2 grew at a rate six tímes slower than the photoheterotrophic one. Its growth continued on polyurethane pads soaked with agar-free medium and was fully inhibited by 0.5 pM DCMU.
In order to evaluate the effect of leaf age on enzymes of carbon and sulphur metabolism, chlorophyll (Chl) and protein contents and the activities of RuBP- carboxylase (RuBPC), ATP-sulphurylase (ATPS), and 0-acetylserinesulphydrylase (OASS) were determined in leaves of different ages from luceme (Medicago sativa L. cv. Lodi and Sewa) plants grown outdoors. The enzymes of sulphur and carbon metabolism were differently regulated throughout development of luceme leaves, as ATPS reached the highest activity at very early stages of leaf growth, when RuBPC activity was negligible. OASS activity inereased 2-fold during leaf expansion, and deereased with leaf senescence. The two cultivars showed rather similar trends of development in Chl, protein content and enzyme activities. The cultivars differed also in the absolute level of enzyme activities and other biochemical parameters.
The exciton equilibration in the light-harvesting complex of photosystem 2 at room temperature was studied with pump-probe experiments under quasi-stationary conditions. The measurements were performed with two dye lasers, which had a pulse diuation of 10 ns and a spectral bandwidth of less than 0.01 nm. The relative probe beam transmission ffom 640-690 nm was recorded at different excitation wavelengths, varied from 645 to 685 nm. Two maxima were observed at 650 nm (Chl b absorption region) and at 680 nm (Chl a absorption region). The relative probe beam transmission in the Chl a region showed a course nearly independent of the pump beam wavelengťh in contrast to a weak dependence in the Chl b region. Measurements of the relative probe beam transmission as a function of pump beam intensity revealed a dominating exciton-exciton annihilation in the Chl a absorption region. In the Chl b region exciton-exciton annihilation was only marginal.