Changes in some Calvin Cycle Enzymes of the Tomato during Acclimation to Irradiance

Publisher Website
Google Scholar
Abstract
The activities of three Calvin cycle enzymes, RuBPc (E.C. 4.1.1.39), 3PGA phosphokinase (E.C. 2.7.2.3) and NADP-G3P dehydrogenase (E.C. 1.2.1.13), and the cytoplasmic enzyme PEPc (E.C. 4.1.1.31) together with soluble protein and chlorophyll were measured in extracts from young tomato leaves during acclimation to a change in irradiance. Leaf area and fresh weight were also measured to show changes due to growth during treatments. Soluble protein had doubled on a unit leaf area basis 7 d after transfer from 100 μmol quanta m−2s−1PAR (low light) to 400 μmol quanta m−2s−1PAR (high light). During this period the protein/chlorophyll ratio rose from 4⋅6 to 10, RuBPc activity almost doubled and PEPc almost trebled. Following the reverse transfer from high to low light, soluble protein decreased by 30% after 7 d and the protein/chlorophyll ratio fell from 12 to 5⋅6. There was no change in RuBPc activity 3 d after transfer from high to low light while PEPc activity decreased by over 30%. There was no decrease in the activity of 3PGA phosphokinase or NADP-G3P dehydrogenase 1 d after transfer to low light, but decreases were apparent after 3 d. The extracted kinase and dehydrogenase when fully activated were able to phosphorylate and reduce 3PGA at more than 2⋅5-fold its calculated rate of synthesis in the leaf. The data are discussed in relation to changes in the CO2 exchange of the leaf.