No 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...

Permeation via acetone of fusicoccin (FC), or of a combination of the three growth regulators, kinetin (K), 2-chloroethyl(phosphonic acid) (ethephon) (E), and gibberellic acid (G) into dry lettuce (Lactuca sativa L. cvs. Grand Rapids and Mesa 659) seeds markedly relieved the inhibiting effects of stress on germination and seedling emergence. Permeation with FC or K+E+G increased dark germination by 80 to 90% at 30°C. At 35°, germination of ‘Grand Rapids’ seeds was enhanced much more by FC than by K+E+G. Both FC and K+E+G increased germination in solutions of NaCl (−4.95 bars) or polyethylene glycol-6000 (−3 bars). In saline medium at 30 and 35°, FC was more active than K+E+G. Hypocotyl and radicle elongation was greater for seeds treated with FC than for seeds treated with other materials in both aqueous and saline media. In soil moistened with water or 0.1 NaCl, emergence of unpermeated ‘Mesa 659’ seeds was 0 to 2% at 25°. Permeation with FC or K+E+G enhanced emergence 65–80% in water, 48–55% in NaCl. FC produced more vigorous seedlings in terms of fresh weight and size than any other treatment including K+E+G. Furthermore, FC generally shortened the emergence time more than K+E+G treatment, the difference being more marked in saline soil.

In axillary meristems laid down just prior or subsequent to commencement of growth regulator applications, exogenous gibberellic acid (GA) alone promoted runner formation. Strongly-inhibited axillary buds with leaf primordia responded to GA + BA (benzyladenine) with runner formation in the June-bearer ‘Fortune’. Few of the inhibited buds of the everbearer ‘Geneva’ responded to GA or GA + BA. Following application of BA alone, inhibited buds of June-bearing cultivars formed lateral crowns (‘Fortune’) or runners (‘Earlidawn’). Runner formation following chilling of June-bearing ‘Fortune’ plants exposed to short days (SDs) occurred from meristems initiated after satisfaction of the cold requirement. Comparable buds on plants receiving no chilling during SDs remained inhibited, as did axillary meristems present during SDs. In contrast, runners formed by chilled, everbearing ‘Geneva’ plants originated from axillary meristems initiated prior to chilling but not from subsequent meristems. Chilling ‘Geneva’ plants during exposure to SDs removed the inhibition from existing axillary meristems and promoted runner formation. Runnering did not occur in activley growing ‘Geneva’ plants maintained under long days (LDs).