Changes of Some Membrane-Associated Enzyme Activities and Degradation of Membrane Phospholipids in Cucumber Roots Due to Ca^<2+> Starvation

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Deprivzition of Ca^<2+>+ from a complete culture medium affected the enzyme activities associated with five membrane fractions of cucmber roots obtained by discontinuous sucrose density gradient centrifugation. The total activity of K^+-ATPase, Cyt. c oxidase and NADPH-Cyt. c reductase of Ca^<2+>-deficient roots, starved for only 4 days, had decreased to 14, 38 and 60% of the activity of the control roots. In general, loss of enzyme activities was accompanied by a shift of activity distribution from the heavier density fractions to lighter ones. The amounts of Ca^<2+> associated with membranes from Ca^<2+>-starved roots decreased to 50-60% of those of the control roots. Both phospholipid and neutral lipid contents in the membranes decreased markedly while the protein content was not changed by Ca^<2+>-deficiency. Phospholipid analysis indicated a drastic drop in the percent composition of phosphatidylinositol but an increase of phosphatidic acid. Also, phospholipase D activity increased remarkably during Ca^<2+> starvation, paralleling the appearance of Ca^<2+>-deficiency symptoms. Thus, the major effects of Ca^<2+> deficiency appear to be to stimulate phospholipase D activity and a reduction in membrane bound Ca^<2+>. These effect may be involved in disorganization of the membrane structure and the changes of enzyme activities associated with the altered membranes.
日本植物生理学会の論文