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Plant and Cell Physiology, 1986, Vol. 27, No. 2 223-232
© 1986

Article

Changes of Some Membrane-Associated Enzyme Activities Degradation of Membrane Phospholipids in Cucumber Roots Due to Ca2+ Starvation

Piyasiri A. J. Yapa1, Toshio Kawasaki and Hideaki Matsumoto2

Institute for Agricultural and Biological Sciences, Okayama University Chuo 2-20-1, Kurashiki, Okayama 710, Japan

2To whom correspondence should be addressed.

Deprivation of Ca2+ 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 Ca2+-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 Ca2+ associated with membranes from Ca2+-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 Ca2+ 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 Ca2+ starvation, paralleling the appearance of Ca2+-deficiency symptoms.

Thus, the major effects of Ca2+ deficiency appear to be to stimulate phospholipase D activity and a reduction in membrane bound Ca2+. These effect may be involved in disorganization of the membrane structure and the changes of enzyme activities associated with the altered membranes.

1Rubber Research Institute of Sri Lanka, Dartonfield, Agalwatta, Sri Lanka.

(Received July 15, 1985; Accepted November 21, 1985)
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