Structure-activity studies with ABA analogs on germination and endo-beta-mannanase activity in tomato and lettuce seeds

The effects of several analogs of ABA were rested on tomato (Lycopersicon e sculentum Mill.) and lettuce (Lactuca? sativa L.) seed germination and on t he ability of these seeds to produce endo-beta-mannanase (EC 3.2.1.78) duri ng and following germination. The (+)-enantiomers of ABA and its analogs we re more effective than the (-)-enantiomers in inhibiting the germination of seeds of both species. Endo-beta-mannanase activity in the tomato endosper m cap during germination was not influenced by ABA or its analogs, regardle ss of whether the seeds completed germination or not. Thus, while there was a structure-activity relationship of the ABA analogs with respect to tomat o seed germination, there was no such relationship with respect to endo-bet a-mannanase activity in the endosperm cap during this event. Post-germinati on enzyme activity in the tomato lateral endosperm region, on the other han d, was inhibited by the (+)enantiomers of`ABA and ia analogs. (-)-Dihydroac etylenic ABA alcohol, a purported competitive inhibitor of ABA, did not rev erse the inhibitory effects of (+)- or (-)-ABA on tomato seed germination; instead, it enhanced the inhibition. Lettuce seed endo-beta-mannanase activ ity was suppressed by most analogs of ABA, and in the presence of (-)-dihyd roABA and (+)-dihydroABA very low amounts of enzyme were produced in the en dosperms of seeds that were able to complete germination. This observation supports the suggestion that there is no cause-and-effect relationship betw een lettuce seed germination and endo-beta-mannanase production.