Effects of Light Intensity on Photosynthetic Carboxylative Phase Enzymes and Chlorophyll Synthesis in Greening Leaves of Hordeum vulgare L

The effects of various light intensities on in vivo increases in activities of phosphoriboisomerase, phosphoribulokinase and ribulose-1, 5-diP carboxylase and on synthesis of chlorophyll were studied in greening leaves of Hordeum vulgare L.

Each enzyme was already present in dark-grown plants, but further increases in activities required both a light treatment of the intact plant and a favorable temperature. The amount of enzymatic activity and chlorophyll developed was governed by light intensity.

Measured activities of phosphoriboisomerase and ribulose 1,5-diP carboxylase were highly correlated with synthesis of chlorophyll at all intensities studied. Measured activity of phosphoribulokinase was correlated with synthesis of chlorophyll only at saturating or near saturating light intensities. At decreasing light intensities the response curves of this enzyme differed from those of chlorophyll and of phosphoriboisomerase and ribulose-1, 5-diP carboxylase. A lag period of phosphoribulokinase increased with decreasing light intensity. After the lag period a rapid rate of increase occurred which did not level off during 48 hours of illumination. Thus, a different control mechanism may be operative in inducing increased activity of this enzyme.