conclusion that arises largely from the observation in some species that inhibitors
of protein and RNA synthesis prevent the increase in certain mobilizing en-
zymes. Examples of enzymes that can be inhibited in this way are isocitrate lyase
in squash cotyledons, lipase in castor bean endosperm, and a-amylase in French
bean cotyledons. Better evidence that the enzymes are newly synthesized is rare;
however, when hydrated cotyledons of watermelon and mung bean are supplied
with D20 the isocitrate lyase of the former and the endopeptidase of the latter
become density labeled. Similar labeling of a-amylase occurs during its produc-
tion in pea cotyledons. A few apparent exceptions have been reported; for
example, a lipase which is present in newly hydrated castor bean endosperm is
likely to have been in the dry seed (Fig. 7.11). And in lettuce, a-galactosidase
and P-mannosidase, which participate in the final stages of hydrolysis of the
galactomannans of the endosperm cell walls, are found in the cotyledons of the
dry seeds.