SUBSTITUTION OF HYDRAZONES FOR THE 4' CARBONYL ON ABSCISIC-ACID RENDERED IT INEFFECTIVE IN A RAPID STOMATAL-OPENING-INHIBITION BIOASSAY

A rapid stomatal bioassay to test abscisic acid (ABA)-like inhibition of stomatal opening was elaborated. The assay was sensitive to low con centrations of ABA (>50% inhibition of opening at 0.02 mu M (+)-S-ABA) and was insensitive to 20 mu M (+/-)-S-ABA-1-(methyl ester), which is consistent with previous work. With the original intent of developing anti-idiotypic antibodies, we made conjugates of ABA at the 4' carbon yl because of its accessibility and known requirements for other posit ions of the ABA molecule in stomatal signal transduction. We found tha t these conjugates lacked ABA-like activity and did not interfere with (+)-S-ABA in the stomatal bioassay, implying the importance of the 4' carbonyl. These observations cast doubt on the feasibility of using a nti-idiotypic antibodies produced through the use of 4'-substituted AB A for the isolation of a guard-cell ABA receptor.