The relative potencies of naturally-occurring S-abscisic acid (S-ABA) and the synthetic ABA analog 8'-acetylene methyl-ester ABA (PBI-429) were determined for selected treatment effects on tomato and Pansy.  In tomato, S-ABA and PBI-429 concomitantly decreased transpiration and above-ground fresh weight and height in a log-linear dose dependent manner.  For these three attributes, ABA analog was about ten times more potent than S-ABA.  In Pansy, while ABA analog was about ten times more potent than S-ABA for reducing transpiration and increasing shelf life than S-ABA, the potency of S-ABA and ABA analog were similar for increasing leaf yellowing.  These results illustrate that the relative potencies of S-ABA and ABA analog are not predictable prior to evaluation and suggest that abscisic acid treatment effects on leaf water loss and yellowing may be separable.

Key word: Abscisic acid (ABA); ABA analog, PBI-429; transpiration inhibition; leaf yellowing; leaf wilting