Control of galactosyl‐sugar metabolism in relation to rate of germination

The storage sugars stachyose and raffinose (galactosyl derivatives of sucrose) are metabolized early during germination of soybean [Glycine max (L.) Merr.] seeds. The activities of four enzymes involved in the catabolism of these sugars were monitored in soybean cotyledons and embryonic axes during a 7-day germination period. An increase in enzyme activities correlated with a decline in galactosyl sugars. In embryonic axes, uridine diphosphate glucose (UDPglc)-hexose-l-P uridyltransferase (EC 2.7.7.12), an enzyme characteristic of the Leloir pathway, predominated over galactose-1-phosphate uridyltransferase (EC 2.7.7.10), an enzyme characteristic of the pyrophosphorylase pathway; whereas in cotyledons, the situation was reversed. There were differences between two cultivars. Ransom and Amsoy, in the levels of UDPglc-4-epimerase (EC 5.1.3.2); but not in glucose-1-phosphate uridyltransferase (EC 2 7.7.9). An accelerated aging treatment had a significant effect on the development of embryonic axes, as measured by dry weight. In vitro aging of seeds reduced the rate of growth and resulted in higher levels of galactose-containing sugars and significantly lower levels of UDPglc-hexose-l-P uridyltransferase. Thus, reduced development may be related to inability to mobilize or utilize stored carbon reserves. However, it has not been proved that the reduced enzyme activity is responsible for the effects of accelerated aging on growth and sugar metabolism.