ACQUISITION OF DESICCATION TOLERANCE BY ISOLATED MAIZE EMBRYOS EXPOSED TO DIFFERENT CONDITIONS - THE QUESTIONABLE ROLE OF ENDOGENOUS ABSCISIC-ACID

The effect of exogenous ABA on acquisition of desiccation tolerance has been well documented for the embryos of several species, including maize (Zea mays L.). Tt has also been suggested that endogenous ABA plays a role in regulating the same phenomena. To test this hypothesis, endogenous ABA was quantified by radioimmunoassay. Our results show that: (1) during embryogenesis in maize, endogenous ABA increases concomitantly with the acquisition of desiccation tolerance; (2) ABA deficient embryos of the vp5 mutant are desiccation intolerant, but tolerance can be induced by exogenous ABA; and (3) desiccation tolerance is acquired if desiccation sensitive embryos undergo a slow drying treatment, during which ABA increases. However, when embryos were preincubated in fluridone to prevent ABA accumulation during slow drying, desiccation tolerance was induced in spite of the low level of endogenous ABA in the embryo. Our results cast doubts on an exclusive role of ABA in the acquisition of desiccation tolerance in maize embryo.