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Plant and Cell Physiology, 1986, Vol. 27, No. 6 1091-1100
© 1986

Article

The Ca2+-Induced Phase Transformation in Soybean Root Microsomal Membranes is a Consequence of Phospholipase Activation

Martin Caffrey1 and Roger R. Lew2,3

1Section of Biochemistry, Molecular and Cell Biology, Clark Hall, Cornell University Ithaca, NY 14853 U.S.A.
2Section of Plant Biology, Division of Biological Sciences, Plant Science Building, Cornell University Ithaca, NY 14853, U.S.A.

Microsomes from soybean (Glycine max L.) roots contain a Ca2+-activated phospholipase D which hydrolyzes phosphatidylethanolamine and phosphatidylcholine to phosphatidic acid. The phosphatidic acid binds Ca2+ in the medium and undergoes a liquid crystal to gel phase transformation (measured by wide-angle x-ray diffraction). The gel phase formation in the microsomes half-saturates at 1 to 10 mM Ca2+. The upper limit for the transition temperature for the microsomes is –10 to 10°C in the native state. After treatment with Ca2+, the transition temperature increases to 35 to 50°C. Under the same experimental conditions, incubation with 10 mM Ca2+ at 4°C causes an increase in phosphatidic acid content from 8 mole % to 49% with a concomitant decrease in phosphatidylethanolamine and phosphatidylcholine from about 22% and 41%, respectively, to 14% each.

These results suggest that Ca2+ effects in systems where Ca2+ plays a multifunctional role be interpreted with caution.

3Present address: Department of Physiology, Yale University School of Medicine, New Haven, CT 06510, U.S.A.

(Received June 15, 1985; Accepted June 13, 1986)
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