Glyoxysomal Malate Synthase of Cucumber: Molecular Cloning of a cDNA and Regulation of Enzyme Synthesis during Germination

A cDNA clone for the glyoxysomal enzyme malate synthase was isolated from a cDNA library made with polyadenylated RNA from the cotyledons of germinating Cucumis sativus L. This cloned DNA sequence was used as a probe to characterize changes in the amounts of malate synthase gene transcripts in cotyledons of cucumber seeds grown both in the light and in the dark. Malate synthase gene transcripts increase in amount to a peak at day 3 or day 4, and thereafter decline. In the light, this rate of decline is significantly greater than in the dark. Measurement of the changes in the amounts of malate synthase by assaying enzyme activity directly, and by immunological reaction with a specific antiserum indicate that the developmentally regulated synthesis of malate synthase in germinating cucumber is brought about primarily by changes in the amount of malate synthase gene transcripts, rather than through a control of translation. Similarly, the effect of light on the amount of malate synthase correlates precisely with its effect on the abundance of malate synthase gene transcripts.