Inhibitors from carob (Ceratonia siliqua L.) : III. Comparisons with abscisic acid

Inhibitory extracts of carob and abscisic acid (ABA) were compared and found to behave differently in three types of tests. The carob inhibitors remained at the origin upon thin-layer chromatography in two different solvent systems while a cis-trans mixture of ABA had Rf's of 2.5 and 3.5 in the first system (chloroform:acetic acid, 95:5), and 3.5 and 4.5 in the second system (benzene:acetic acid:water, 8:3:5). When ABA and carob extract were mixed and then chromatographed, the ABA had the same Rf values as ABA chromatographed alone.Assays utilizing light-grown, dwarf peas showed that a weight ratio of 1000: 1 ABA:gibberellic acid (GA3) was necessary to inhibit GA3-induced growth by 50% while carob fraction C is inhibitory to GA3 at a ratio of 17:1. The amount of ABA which inhibited 50% of the growth induced by 0.05 μg GA3 reduced the endogenous growth of both dwarf and non-dwarf pea seedlings; in contrast, concentrations of carob extract up to 100 times greater than the amount necessary for 50% inhibition of the growth response caused by 0.05 μg GA3 did not affect endogenous growth.Only very small amounts of inhibitory activity from carob extract were transferred from water to chloroform at a pH (2.0) at which most of the ABA was transferred.