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

The glyoxylate cycle, which is associated with postgerminative seedling growth in many oil-rich seeds, has not been extensively studied in relation to the seed's internal milieu during development and germination. Enzyme activities 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 [Glycine max (L.) Merrill] cv. Ohio FG1] seed cotyledons and axes at nine stages of development and during the first 30 h of germination. Enzyme activity was compared to qualitative transcript levels at four stages of development from the beginning of seed fill to harvest maturity, and after 4, 12, 22 and 30 h of imbibition. Development and germination stages were characterised by osmotic potential and water content. Cytochrome c oxidase and MDH were 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. During 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 imbibition. Glyoxylate cycle enzyme accumulation was associated with low sucrose and high lipid concentrations. It is concluded that soybean cotyledons and axes show coordinate glyoxylate cycle enzyme accumulation that is correlated with the period of sucrose starvation and lipid elevation during both seed maturation and germination.