Role of Auxin and Polyamines in Adventitious Root Formation in Relation to Changes in Compounds Involved in Rooting

Abstract

An attempt was made to identify some cellular components that control adventitious root formation at the base of hypocotyl cuttings of mung bean (Vigna radiata L. cv. 105). Three phases of the adventitious root formation process were identified; induction (0-24 h), initiation (24-72 h), and expression (after 72 h). The lower peroxidase activity during the induction period (0-24 h) corresponded with the first peak of IAA at 24 h which indicated termination of the induction phase. A peak of peroxidase activity with low IAA levels at 72 h signaled the termination of the initiation phase. After 72 h, peroxidase activity declined and IAA levels increased slowly and this was characterized as the expression phase. IAA-oxidase activity could be inversely correlated with endogenous IAA levels. Endogenous putrescine and IAA increased simultaneously both at the induction and initiation phase, and might have a combined role in adventitious root formation. Spermidine and spermine levels did not change significantly throughout these phases. The pattern of diamine oxidase and polyamine oxidase (DAO/PAO) activities was inversely correlated with endogenous polyamine levels only during the induction phase. Levels of H 2 O 2 , which is involved in IAA and phenol oxidation and also in cell wall xylogenesis, were positively correlated with DAO/PAO activity because H 2 O 2 is one of the end products of PA oxidation. An inverse relationship between phenol content and polyphenol oxidase activity was observed during rooting of mung bean cuttings. Compared with controls, IBA-(10 -5 M) or PUT-(10 -4 M) treated cuttings exhibited increased levels of IAA, putrescine, phenol and H 2 O 2 , decreased IAA-oxidase activity, and increased DAO/PAO, peroxidase, and polyphenol oxidase activities. An early appearance of the second peak of putrescine and phenol at the end of the initiation phase (72 h) was observed in cuttings treated with IBA or PUT. On the basis of IAA levels and peroxidase activity, there was no change in the duration of different rooting phases due to IBA or PUT treatments. However, on the basis of endogenous PUT levels, treatment with IBA or PUT reduced the total duration of the initiation and expression phases.