Abscisic Acid and the Germination of Thermodormant Lettuce Fruits (Lactuca sativa cv. Grand Rapids). The Fate of Isotopically Labelled Abscisic Acid

Abstract

ABA inhibits the germination of Grand Rapids lettuce seeds at a temperature at which photoblastism is not observed. This ABA inhibition can be overcome by GA, or cytokinin, or red light acting alone or in concert. At high levels of ABA the ameliorative effects of GA, cytokinin or red light are not manifest and it is suggested that lettuce seeds' response to a given level of ABA is temperature dependent, and any interaction which may be observed between ABA and other regulators, or red light, likewise is temperature dependent. Seeds only actively metabolize ABA after germination is complete though ABA does influence the germination process proper. Some radioactivity, originally applied as 14C ABA, cannot be extracted from 14C ABA treated seeds by methanol, and this “fixed” ABA can constitute more than 50% of the activity taken up by the seeds. High levels of “fixed” ABA are found in seeds which do not germinate. As well as this “fixed” ABA two labelled metabolites arise in seeds treated with 14C ABA. The levels of these rise in seed extracts as the level of extractable ABA decreases. Whilst ABA can affect germination our results do not allow us to assign a specific regulatory role to ABA in seed germination.

Indirect effect of abscisic acid on the induction of secondary dormancy in lettuce seeds

“…The pattern of distribution of radioactivity after TLC in metabolic extracts of lettuce seed cv. Olof (Fig, 5) iooks similar to data obtained by Robertson and Berrie (1977) with seeds of the cultivar Grand Rapids in the same solvent system. As in their study, the exact nature of the metabolites remained obscure, lt could only be excluded that decarboxylation takes a major part in the metabolic conversion of ABA in lettuce seeds (Tab.…”

Interactions between hydrogen cyanide, gibberellin, abscisic acid and red light in germination of lettuce seeds

“…The data presented here also confirm the reversibility of ABA inhibition of lettuce seed germination by GA or light treatments (Poggi-Pellegrin andBulard 1976, Robertson andBerrie 1977). The fact that in both cases ABA applied later than the stimulatory factor caused lower inhibition (higher percentage germination) than when applied before GA, or light, seems to indicate the secondary character of ABA action upon the mechanisms triggered by germination stimulators.…”

“…Black 1969, and abscisie aeid inhibits their germination (Reynolds and Thompson 1973). Experiments with Grand Rapids seeds have shown that ABA inhibition can be reversed by GA,, GA4 or light (Poggi-Pellegrin andBulard 1976, Robertson andBerrie 1977).…”

Genetic Variation for Lettuce Seed Thermoinhibition Is Associated with Temperature-Sensitive Expression of Abscisic Acid, Gibberellin, and Ethylene Biosynthesis, Metabolism, and Response Genes

“…Exposure to ethylene, GA, and red light can increase the upper temperature limit of lettuce seed germination, and exposure to ABA can decrease it (Reynolds and Thompson, 1973;Saini et al, 1986Saini et al, , 1989Dutta and Bradford, 1994;Kristie and Fielding, 1994;Gonai et al, 2004). The sensitivity of lettuce seed germination to inhibition by ABA is enhanced at higher temperatures (Robertson and Berrie, 1977;Roth-Bejerano et al, 1999).…”