Endogenous Abscisic Acid Levels in Germinating and Nongerminating Lettuce Seed

Abstract

The concentrations of abscisic acid in Grand Rapids lettuce (Lactuca sativa L.) seeds imbibed under conditions which promote or inhibit germination were determined by electron capture-gas chromatography. The concentration of abscisic acid in dry seeds was 12 to 14 nanograms per 100 milligrams. During 24-hour imbibition, the abscisic acid content diminished more rapidly during conditions which allow germination (25 C in (3,11,12,18). Similarities in the effects of high temperature (35 C) and ABA and their interactions with kinetin and GA3 have been shown recently (7).Probably the absence of germination in darkness or at high temperatures is controlled at some stage by a high level of inhibitor(s) and/or a low level of promoter(s) (6). Gas chromatographic evidence for the presence of ABA in dry Grand Rapids lettuce seed has recently been reported (19). The present investigation was undertaken to determine the contents of ABA in Grand Rapids lettuce seeds during imbibition under conditions which prevent and allow germination. MATERIALS AND METHODSIn the light versus dark experiment, Grands Rapids lettuce (Lactuca sativa L.) seeds were imbibed at 25 C in diffuse white light or in total darkness. In the 25 versus 35 C temperature experiments, seeds were imbibed in diffuse white light at these two tem- Seeds (400 mg dry weight) were collected in test tubes and cold 80% ethyl alcohol was added. Seeds from the dark treatment were collected under a dim green safelight. Tubes with samples were then stored at -30 C until homogenized. Seed samples were homogenized in cold ethyl alcohol (80%/) in a TenBroeck homogenizer and transferred to flasks, the final volume being 40 ml. The homogenates were left overnight at 5 C on a shaker.The preparations were then filtered in vacuo through a Buchner funnel, the filtrates were collected in round bottomed flasks, and the extract was evaporated to near dryness using a rotary film evaporator under vacuum.Extract purifications were based on the method described by Seeley (14). After evaporating the ethyl alcohol, the residue was taken up in water, and the pH was adjusted to 8.3 with 10% ammonium hydroxide. The aqueous extract was partitioned three times with equal volumes (30 ml) of dichloromethane which was discarded. The aqueous fraction was adjusted to pH 2.6 with 10% HC1 and again partitioned three times with dichloromethane. The dichloromethane phases were pooled and evaporated to dryness. The residue was quantitatively transferred with ethyl acetate and divided equally between two test tubes and the ethyl acetate evaporated with a stream of dry nitrogen gas.Quantitative determination of ABA in the seed extracts was achieved by adaptation of the electron capture-gas chromatography techniques described by Seeley and Powell (15), Seeley (14), and Braun (2). The present determinations were performed using a Perkin-Elmer 900 gas chromatograph equipped with a 3% OV-1 column and a Nickel-63 electron capture detector operated in the pulsed voltage mode (10,000 pulses/sec).At th...

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

“…Our results, while not contradictory to, do not wholly agree with those of Braun and Khan (1975) and Poggi‐Pellegrin and Bulard (1976) who used the cultivar Grand Rapids, and are not in complete agreement with Aspinall et al (1967) who used Great Lakes. We have found that either GA or cytokinin alone can overcome ABA induced inhibition of germination.…”

Seed dormancy and ABA metabolism in Arabidopsis and barley: the role of ABA 8′‐hydroxylase

“…Other studies on barley (Wang et al. , 1995), wheat (Ried and Walker‐Simmons, 1990), lettuce (Braun and Khan, 1975) and tobacco (Grappin et al. , 2000) have also all found higher ABA levels in imbibed D grains/seeds than in ND grains/seeds.…”

Hormones in Seed Dormancy and Germination

“…The data collected so far do not give an unambiguous confirmation of that assumption. In some cases the light stimulus causes a rapid increase 0 f hormone level (GA4 in apple embryos, Smolenska and Lewak, 1971, GA9 in lettuce seeds, Bianco and Bulard, 1981), but in other cases changes in the content of hormones arc not observed (ABA in lettuce seeds, Khan and Braun, 1975;GA4 and GA7 in the same material; Bianco and Bulard, 1981). Similarly, chilling of imbibed apple or sugar mapple seeds results in pronounced rise in GAs and CKs levels.…”