Germination and dormancy of abscisic acid- and gibberellin-deficient mutant tomato (Lycopersicon esculentum) seeds. Sensitivity of germination to abscisic acid, gibberellin, and water potential.
Ni, B.R. and Bradford, K. J.
Plant physiology. Vol: 101 Issue: 2 Pages: 607-617.
1993
บทคัดย่อ
Germination responses of wild-type (MM), abscisic acid (ABA)-deficient (sitw), and gibberellin (Ga)-deficient (gib-1) mutant tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds to ABA, GA 4+7, reduced water potential, and their combinations were analyzed using a population-based threshold model (B.R. Ni and K.J. Bradford [1992] Plant Physiol 98: 1057-1068). Among the three genotypes, sitw seeds germinated rapidly and completely in water, MM seeds germinated more slowly and were partially dormant, and gib-1 seeds did not germinate without exogenous GA 4+7. Times to germination were inversely proportional to the differences between the external osmoticum, ABA, or GA 4+7 concentrations and the corresponding threshold levels that would either prevent (reduced water potential b, log[ABA b]) or promote (log[GA b]) germination. The sensitivity of germination to ABA, GA 4+7, and reduced water potential varied widely among individual seeds in the population, resulting in a distribution of germination times. The rapid germination rate of sitw seeds was attributable to their low mean reduced water potential b (-1.17 MPa). Postharvest dormancy in MM seeds was due to a high mean reduced water potential b (-0.35 MPa) and a distribution of reduced water potential b among seeds such that some seeds were unable to germinate even on water. GA 4+7 (100 micromolar) stimulated germination of MM and gib-1 seeds by lowering the mean reduced water potential b to -0.75 MPa, whereas ABA inhibited germination of MM and sitw seeds by increasing the mean reduced water potential b. The changes in reduced water potential b were not due to changes in embryo osmotic potential. Rather, hormonal effects on endosperm weakening opposite the radicle tip apparently determine the threshold reduced water potential for germination. The analysis demonstrates that ABA- and Ga-dependent changes in seed dormancy and germination rates, whether due to endogenous or exogenous growth regulators, are based primarily upon corresponding shifts in the reduced water potential thresholds for radicle emergence. The reduced water potential thresholds, in turn, determine both the rate and final extent of germination within the seed population.