Invertases in Oat Seedlings

Abstract

The soluble invertase activity in etiolated Avena seedlings was highest at the apex of the coleoptile and much lower in the primary of leaf, mesocotyl and root. The activity in all parts of the seedlings consisted of 2 invertases (I and II) which were separated by chromatography on diethylaminoethyl-cellulose. Both enzymes appeared to be acid invertases, but they differed in molecular size, pH optimum and the kinetic parameters Km and Vmax of their action of sucrose, raffinose and stachyose. Invertase II had low stability at pH 3.5 and below, and exhibited high sensitivity to Hg2+, with complete inhibition by 2 mM HgCl2. Segments of coleoptiles incubated in water lost about two-thirds of the total invertase activity after 16 h. The loss of activity was due primarily to a decrease in the level of invertase II. The loss of invertase was decreased by IAA, 2,4-D and .alpha.-naphthaleneacetic acid but not by .beta.-naphthaleneacetic acid and p-chlorophenoxyisobutyric acid. Conditions that inhibited auxin-induced growth of the segments (20 mM CaCl2 and 200 mM mannitol) also blocked the auxin effect on invertase loss.