Growth Inhibition by Lysine Plus Threonine: Comparative Inhibition Profiles betweenFloury-aand Normal Maize Embryos1

摘要

Lysine and threonine, either alone or in combination, were tested for their effects on growth offloury-αmutant and DY normal embryos of maize in culture. At 1 mM of lysine, no inhibitory effect was observed on either type of embryo, although at 2.5 mM slight inhibitions were observed, principally on the root and shoot lengths. The inhibition profiles by threonine from 0.5 to 2.5 mM were similar to those by lysine only in thefloury-αembryos; in the normal DY embryos, threonine produced a marked inhibition, especially on the root and shoot length. In conjunct inhibition experiments, the profile of inhibition obtained forfloury-αembryos by variable levels of lysine with a constant level of threonine were always identical to that by variable levels of threonine with a constant lysine level. On the other hand, in the normal DY embryos, the extent of the inhibitory effect by variable levels of lysine with a Constant threonine level was much greater than that by variable levels of threonine with a constant lysine level. The involvement of homoserine dehydrogenase of thefloury-αembryo in the lesser sensitivity for feedback inhibition by threonine is discus