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

Abstract

Summary. 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 Hordeutn vullgare L.Each enzyme was already present in dark-grown plants, but further increases in activities required both a light treatiment of the intact plant and a favorable temperature. The amount of enzymatic activity and chlorophyll developed was governed bv 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 incrcased activity of this enzyme. (3,9), phosphoribulokinase (9), and ribulose-1,5-diP carboxylase (15,22), increased in activity during greening of barley leaves. Increased activity of phosphori,boisomerase (8) and ribulose-1,5-diP carboxylase (8,13) in greeninig leaves has been demonstrated, but the response of phosphoribulokinase has not been reported. Also, further' investigation was required to determine the response of each of the 3 enzymes in leaves greening at varying light intensity.The relationship of increasing enzymatic activitv to synthesis of chlorophyll in greening leaves is not clear. Several studies indicate a close correlation between the 2. Tromn (20) suggests that fraction 1 protein (23), which contains ribulose-1,5-diP carboxylace (17, 18,20,21), may be part of the protein constituent of protochlorophyll holochrome. This indicates an intimate relationship between synthesis of chlorophyll and that of ribulose-1,5-diP carboxylise. Another report (7) indicates that increased enzymatic activity may be related more to structural development of the chloroplast.The object of the present study was to determine how phosphoriboisomerase, phosphoribulokinase andl ribulose-1,5-diP carboxylase respond in plants treated with varying light intensities and, concurrently, to investigate the relationship of increasing enzymatic activity to synthesis of chlorophyll.

Influence of Age and Illumination on Distribution of Several Calvin Cycle Enzymes in Greening Barley Leaves

“…Although light-initiated increases in enzymatic activities did not occur without chlorophyll accumulation, the relationship may still be indirect between activities of the carboxylative phase enzymes and accumulation of chlorophyll. Huffaker et al (7) showed that the linear correlation of phosphoribulokinase activity with chlorophyll content was lost at low intensities of illumination. Benedict and Kohel (2) recently reported that the increase in activity of ribulose-1,5-diP carboxylase is not correlated with chlorophyll accumulation in virescent cotton leaves.…”

“…Distribution of area of 50 leaf sections, phosphoriboisomerase activity, phosphoribulokinase activity, ribulose-l , 5-diP carboxylase activity, soluble protein, and total chlorophyll in different leaf sections after various periods of illumination. All seedlings were grown in darkness for 7 days before illumination at 10,760 lux. Standard errors of the difference between means of illumination periods within a section, and between section means within an illumination period, respectively, were 1.9, 2.6 (Fig.…”

“…Light treatments, nutrient solutions, and preparation of ribulose-1, 5-diP were as previously reported (7). Phosphoriboisomerase, phosphoribulokinase, and ribulose-1,5-diP carboxylase were assayed as reported previously (7) except that 10 ,umoles of KH'4CO3 with a specific radioactivity of 2 X 105 cpm/,umole were used in the assay for ribulose-1 , 5-diP carboxylase activity.…”

Evidence for Lack of Turnover of Ribulose 1,5-Diphosphate Carboxylase in Barley Leaves

“…In barley leaves, several of these processes proceed very rapidly during the first 24 hrs of light and reach a steady state sometime after about 36 to 48 hr of light (6). Hellebust and Bidwell (5) observed that turnover of soluble protein in wheat leaves was fastest when the leaves were either growing or biochemically differentiating.…”

“…After growth or biochemical differentiation was completed, the turnover was very slow. Growth was not a confounding factor in our work, since the experiments were begun only after the first leaf had completed its growth (6 (Fig. 1).…”