Polyamines as biomarkers for plant regeneration capacity: improvement of regeneration by modulation of polyamine metabolism in different genotypes of indica rice

The importance of cellular polyamine (PA) levels and the ratio of putrescine (Put) to spermidine (Spd) ibr plant regeneration ability via somatic embryogenesis in several commercially grown indica rice varieties is reported here.' The genotypes namely NDR-624, IR-20, IR-36, BJ-1 (having Put:Spd ratio similar to 2.3) showed superior plant regeneration while KL, PB-1 and TN-1 (having Put:Spd ratio similar to 3.8) showed moderate plant regeneration ability. The genotypes namely HS, Bindli, DV-85, ACB-72, IR-64 and IR-72 (having Put:Spd ratio similar to 5.0) showed poor plant regeneration ability. In contrast KH-7 (Put:Spd ratio similar to 10.0) showed no response at all. Favorable modification of cellular PA titers and their Put:Spd ratio by the addition of exogenous PAs (Put, Spd) or their biosynthesis inhibitor, difluoromethylarginine (DFMA) led to the induction/promotion of plant regeneration in poorly responding genotypes, These results showed a close relationship between cellular PA levels and their Put:Spd ratio with in vitro morphogenetic capacity in indica rice and suggest that the cellular PAs and Put:Spd ratios are important determinants (biomarkers) of plant regeneration ability in indica rice, and the improvement/induction of plant regeneration in morphogenetically poor and recalcitrant species could be achieved by modulating PA metabolism. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.