Acidification, growth promoter, and red light effects on germination of skotodormant lettuce seeds (Lactuca sativa)

Abstract

promoter, and red light effects on germination of skotodormant lettuce seeds (Lnctucn snrivn). Can. J. Bot. 62: 1 108-1 1 15. Increasing the period of dark storagc (DS) within a uniform seed lot of lettuce (Lncrucn snrivn L. cv. Grand Rapids) increased the degree of secondary dormancy (skotodormancy) induced, as evidenced by a loss of sensitivity to red light (R) and growth promoters such as gibberellin A, (GA,), kinetin, thiourea, and ethylene. Differential degrees of skotodormancy were induced in lettuce seeds from three different sources (lot I < lot 11 < lot 111). Either R or GA3 significantly increased the germination of skotodormant seeds if seeds were first immersed in strongly acidic solutions (pH 5 3.0) and thcn rinsed with water. Thc critical factor was found to be pH, not ionic strength. Promotion of germination by R or GA, was positively related to increasing acidity, and also to the duration of DS. Sensitivity of the germination rcsponse to acid immersion varicd with the sced lots. as little as 1 s being effective with some seeds. Acid treatment thus cnables skotodormant seeds to recover much of their responsiveness to R and GA,. Extended DS (21 days) produced such pronounced skotodormancy (seed lot 111) that acid immersion followed by usual R and GA, produced only 10% germination. Continuous R or a seed-piercing treatment produced complete germination in otherwise skotodormant seeds. Responsiveness of germination to thiourea, kinetin, and ethylene, however, was not regained by treatment with acid. The action of these three chemicals on skotodormant seeds thus seems to be dependent on an active phytochrome and GA,-sensitive system. Acid-immersion treatments appear primarily to weaken membrane barriers of the endosperm cells, with resulting increased sensitivity of seeds to R treatment and GA, penetration.HSIAO, A. I., W. VIDAVER et W. A. QUICK. 1984. Acidification, growth promotcr, and red light effects on germination of skotodormant lettuce seeds (Lnctucn sativa). Can. J. Bot. 62: 1 108-1 1 15. L'accroissement de la pCriode d'entreposagc a I'obscuritC (DS) d'un lot uniforme de graines de laituc (Lactuca sariva L. cv. Grand Rapids) augmente le degrC de dormance secondaire (scotodormance) induite, ainsi que I'indiquent la perte de sensibilitk i la lumiere rouge (R) et aux substances de croissance telles que la gibbkrelline A, (GA3). la kinktine, la thio-urCe et I'Cthylkne. Des degrCs differents de scotodormance ont Ct C induits chez des graines de laitue de trois sources diffkrentes (lot I < lot I1 < lot 111). La lumiere rouge ou le GA, augmentent significativement la germination des graines scotodormantes si celles-ci sont d'abord immergCes dans une solution trks acide (pH 5 3,0), puis rincCes i I'eau. Le factcur critique est le pH et non la force ionique. La stimulation de la germination par les facteurs R ou GA, est relike positivement au taux d'aciditC ainsi qu'i la durCe de la pCriode DS. La sensibilite de la rCponse germinative i l'immersion dans une solution acide varie selon la source des grai...

The roles of inorganic nitrogen salts in maintaining phytochrome- and gibberellin A3-mediated germination control in skotodormant lettuce seeds

“…The study confirmed the findings of Hsiao (1992), Hsiao and Vidaver (1989), and Hsiao et al (1984) that the capacity for R or FR light sensing can be stored in fully imbibed secondarily dormant Grand Rapids lettuce seeds, but remains inactive until the seeds are acidified and incubated in water. Earlier work (Hsiao et al 1984) reported that acid treatment increased the sensitivity of skotodormant seeds to subsequent R or GA 3 treatment and also increased amino acid leaching into immersion solutions. The effect of acidification appeared to be due to a scarification-like effect on seed envelope membranes.…”

“…The deeper dormancy of skotodormant over primarily dormant lettuce seeds may be due to reduced levels of preexisting Pfr and endogenous GA 3 in skotodormant seeds (Hsiao et al 1984). Such seeds normally require both systems to induce complete germination (Hsiao and Vidaver 1989, Hsiao et al 1984, Speer et al 1974, whereas either one of the phytochrome or GA promotion systems is sufficient to terminate primary dormancy (Table 1).…”

“…Such seeds normally require both systems to induce complete germination (Hsiao and Vidaver 1989, Hsiao et al 1984, Speer et al 1974, whereas either one of the phytochrome or GA promotion systems is sufficient to terminate primary dormancy (Table 1). The skotodormancy of 10-day DS seeds imbibed in inorganic nitrogen salts (Tables 2 and 3) or in PEG (Tables 4 and 5) can be overcome by either terminal R or GA 3.…”

“…Grand Rapids) given a 5-min far red light (FR) irradiation 0.5 h after the onset of imbibition, followed by extended dark storage (DS) at 20~ (Hsiao 1992, Hsiao and Vidaver 1989, Hsiao et al 1984, Vidaver and Hsiao 1975. Terminal treatments of red light (R) or growth promoters such as gibberellin A 3 (GA3) do not normally initiate appreciable germination in skotodormant seeds.…”

Roles of Soluble Sugars in Protecting Phytochrome- and Gibberellin A3-Mediated Germination Control in Skotodormant Lettuce Seeds

“…Grand Rapids seeds were from the same seed lot as those used in earlier studies (Hsiao and Quick 1996, Hsiao and Vidaver 1989, Hsiao et al 1984. They had been stored at −20°C and mainAbbreviations: DS, dark storage; R, red light; GA 3 , gibberellin A 3 ; FR, for red light; ANOVA, analysis of variance; GLM, General Linear Model; LSD, least squares difference; Pfr, phytochrome far-redabsorbing form.…”