Accumulation of glyoxylate cycle enzymes in soybean seed embryo tissues during development and germination

The glyoxylate cycle, which is associated with postgerminative seedling gro wth in many oil-rich seeds, has not been extensively studied in relation to the seed's internal milieu during development and germination. Enzyme acti vities for three glyoxylate cycle enzymes [malate synthase (MS), isocitrate lyase (ICL), and malate dehydrogenase (MDH)] and a mitochondrial electron transport system enzyme (cytochrome c oxidase) were examined in soybean [Gl ycine max (L.) Merrill] cv. Ohio FG1] seed cotyledons and axes at nine stag es of development and during the first 30 h of germination. Enzyme activity was compared to qualitative transcript levels at four stages of developmen t from the beginning of seed fill to harvest maturity, and after 4, 12, 22 and 30 h of imbibition. Development and germination stages were characteris ed by osmotic potential and water content. Cytochrome c oxidase and MDH wer e found at all stages of seed development and germination. Malate synthase and ICL activities and mRNA expression were first detected at similar (-2.0 MPa. at 55% water content) water status, about 14 d from the beginning of seed fill in the axes and at physiological maturity in the cotyledons. Duri ng seed germination, the axes showed enzyme accumulation from 4 to 30 h of imbibition while the cotyledons showed ICL mRNA without activity at 12 h of imbibition and ICL and MS mRNA and activities from 22 to 30 h of imbibitio n. Glyoxylate cycle enzyme accumulation was associated with low sucrose and high lipid concentrations. It is concluded that soybean cotyledons and axe s show coordinate glyoxylate cycle enzyme accumulation that is correlated w ith the period of sucrose starvation and lipid elevation during both seed m aturation and germination.