Effect of plant growth hormones and polyamines on ornithine decarboxylase activity during the germination of barley seeds

Abstract

Gibberellic acid (GA3) and β‐indolylacetic acid (IAA), two of the well known growth hormones, induce four fold the activity of ornithine decarboxylase (ODC) during the germination of barley seeds (Hordeum vulgare L. var. Beca). The optimal concentration for induction of ODC was 10–5M for GA3 and 10–3M for IAA. When 10–3M of a polyamine, putrescine or spermidine, is added to the growth medium, ODC activity is significantly inhibited. This inhibition is due to the induction of a protein inhibitor of ODC (antizyme), whose apparent molecular weight is 16 000 ± 2 000 daltons. Addition of GA3 to cultures which have been grown for 50 or 98 h in the presence of polyamines, abolishes the observed inhibition of ODC activity, while in the reverse experiment, addition of polyamines at 50 or 98 h does not affect the ODC activity induced by GA3. Cadaverine, a physiological plant diamine, enhances ODC activity; whereas 1,8‐diaminooctane (the alkyl analogue of spermidine) does not have any effect.