ACTIVITY AND ISOFORMS OF MALATE-DEHYDROGENASE IN MAIZE CULTIVARS WITHHIGH AND LOW OIL CONTENT

The activity, subcellular location, and isoforms of malate dehydrogena se (MDH, EC 1.1.1.37) in 1- to 10-day-old maize seedlings (Zea mays L. ) were studied using lines distinguished by their high (5.5 - 7.2%) or low (1.5 - 2.2%) oil content in seeds. MDH activity in the scutellum of high-oil-yielding lines was 30 - 50% higher than in low-oil-yieldin g lines. This elevated MDH activity was due to a relatively high conte nt of MDH-proteins in glyoxysomes and mitochondria, but not in the cyt osol. There were no cultivar-specific differences in MDH activities in roots and leaves. The number of MDH isoforms present in the scutellum was higher in the lines with low oil content than in high-oil-yieldin g lines (6 - 8 and 4 - 6, respectively), but the activity of glyoxysom al MDH isoforms was substantially higher in high-oil-yielding plants. It is concluded that the number of expressed MDH isozymes varies in ac cordance with specialized metabolic patterns that evolved in maize scu tellum in relation to reserve lipid mobilization.