Diamine Oxidase Activity During the Germinative and Post-Germinative Growth of the Embryonic Axis in Chickpea Seeds

Diamine oxidase (DAO, EC 1.4.3.6.), which participates in oxidative catabolism of polyamines (PAs), was not detected in the dry viable chickpea (Cicer arietinum L.) seeds. From the time when the embryonic axis acquired an aerobic metabolism, DAO increased concomitantly with the growth of the embryonic axis and at the same time with the deterioration of the cotyledons, although in these organs the values were clearly lower than in the axis. The highest DAO activity in the embryonic axis of seedlings grown for 72 and 96 h was found in the elongation, differentiation and hypocotyl zones, while the lowest was in the apex and plumule. The absence of cotyledons promoted the early appearance of DAO in the embryonic axis. When germination occurred at supraoptimal temperatures (30 – 35 °C), DAO activity was sharply inhibited both in the cotyledons and in the embryonic axis. This inhibition was accentuated further in the presence of cyclohexylamine, an inhibitor of spermidine synthase activity, to such a degree that DAO was undetectable in the cotyledons. DAO inhibition by EGTA and the pronounced reversal induced by Ca²⁺ implies that calcium may be related to DAO activity. The presence of putrescine, spermidine and spermine in the germination medium stimulated DAO activity, although this activity was inhibited when the exogenous PA was cadaverine.