Induction of laterals in root cultures of eggplant ( Solanum melongena L.) in hormone-free liquid medium: : A novel system to study the role of polyamines

Abstract

Root cultures of eggplant ( Solanum melongena L.) offer an excellent in vitro system to study the role of polyamines in growth and differentiation as there is no requirement for exogenous phytohormones for root elongation and differentiation of lateral roots in the liquid culture medium. The diamine putrescine (Put) is toxic for root growth at 1 mM and it was also found to be inhibitory for differentiation of laterals at 0.5 and 1 mM. In contrast, the polyamine spermidine (Spd) dramatically increased both root length and number of laterals at 0.5 and 1 mM. The effect of exogenously supplied polyamine biosynthetic inhibitors was also studied. Difluoromethylarginine (DFMA) at 0.5 and 1 mM strongly inhibited root growth and differentiation of laterals while difluoromethylornithine (DFMO) was found to be weak inhibitor of both processes at 1 mM. Methylglyoxal bis (guanylhydrazone) (MGBG) was inhibitory for root growth and differentiation at all concentrations tested with 1 mM being toxic; bis (cyclohexylammonium) sulphate (CHA) had similar effects though much higher concentrations were required to induce similar effects. Application of 0.5 mM Spd along with either 1 mM DFMA or 0.5 mM MGBG resulted in reversal of inhibition caused by these inhibitors. These results demonstrate that polyamines, particularly spermidine, are intricately involved in root growth and differentiation of lateral roots.