THE PHYSIOLOGICAL-ROLE OF ABSCISIC-ACID IN ELICITING TURION MORPHOGENESIS

The exogenous application of hormones has led to their implication in a number of processes within the plant. However, proof of their functi on in vivo depends on quantitative data demonstrating that the exogeno us concentration used to elicit a response leads to tissue hormone lev els within the physiological range. Such proof is often lacking in man y investigations. We are using abscisic acid (ABA)-induced turion form ation in Spirodela polyrrhiza L. to investigate the mechanism by which a hormone can trigger a morphogenic switch. In this paper, we demonst rate that the exogenous concentration of ABA used to induce turions le ads to tissue concentrations of ABA within the physiological range, as quantified by both enzyme-linked immunosorbent assay and high-perform ance liquid chromatography/gas chromatography-electron capture detecti on analysis. These results are consistent with ABA having a physiologi cal role in turion formation, and they provide an estimate of the chan ges in endogenous ABA concentration required if environmental effecter s of turion formation (e.g. nitrate deficiency, cold) act via an incre ased level of ABA. In addition, we show that the (+)- and (-)-enantiom ers of ABA are equally effective in inducing turions. Moreover, compar ison of the ABA, levels attained after treatment with (+)-, (-)-, and (+/-)-ABA and their effect on turion induction and comparison of the e ffectiveness of ABA on turion induction under different pH regimes sug gest that ABA most likely interacts with a plasmalemma-located recepto r system to induce turion formation.