Reversal of the inhibitory action of abscisic acid by benzyladenine in excised watermelon cotyledons

Cotyledons of watermelon ( Citrullus vulgaris Schrad. cv. Fairfax) were excised from the embryo after 24 h of imbibition and cultured for several days on filter paper with water or abscisic acid (ABA) solution. In some experiments the cotyledons were pretreated with benzyladenine (BA) for times ranging from 5 min to 2 h before transfer to ABA.
A treatment with 10^?5 M ABA blocked all developmental parameters examined (growth and increase in appropriate markers for glyoxysome, peroxisome and plastid development). This blocking can be prevented by an initial treatment with 10^?4 M BA for 2 h. This pretreatment with BA overrides the action of ABA: the final developmental responses are not just restored to the level of the water control, but they are almost as high as those obtained by treating the cotyledons with BA only. If BA is administered for three days together with ABA the reversal of inhibition is much less efficient.