ROLE OF ENDOGENOUS AUXIN AND POLYAMINES IN ADVENTITIOUS ROOT FORMATION IN MUNGBEAN CUTTINGS

Exogenous application of putrescine (10 -4 M) markedly improved the number of second order root and second order root length per cutting, whereas, spermidine (10 -9 M) and spermine (10 -5 M) had no significant effect on adventitious root formation in mungbean cuttings. IBA (10 -5 M) was more effective than putrescine in rooting performance. Three phases of adventitious root formation process could be identified namely, induction (0-24h), initiation (24-72h) and expression phase (after 72h). High levels of free IAA, Putrescine (PUT) and low peroxidase (POX) activity were observed during the induction phase. IBA (10 -5 M) treated cuttings showed higher levels of IAA and PUT as well as POX activity than control cuttings. In short-term estimation (0-24h), the free IAA peak (6h) which preceded the PUT peak (12h), might be the reason of initiation of the induction phase of rooting. Experimenting with the inhibitors of polyamine biosynthesis, DFMO, (10 -4 M, α- difluoromethyl ornithine) and DFMA (10 -4 M, α- difluoromethyl arginine) it was observed that DFMO was more inhibitory than DFMA in adventitious root formation and hence ODC (ornithine decarboxylase) pathway might be the preferred pathway for puterscine biosynthesis during adventitious root formation in mungbean. AG (amino guanidine), which inhibits the conversion of putrescine to A- pyrroline and then to GABA (γ- aminobutyric acid), inhibited rooting. CHA (cyclohexylamine), which inhibits the conversion of puterscine to spermidine, on the contrary, favoured rooting. Further, exogenous application of GABA also promoted rooting. The results thus point to the involvement of putrescine and its degradation product GABA in adventitious root formation in mungbean cuttings.