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The gibberellins have been established as effective fruit setting agents (5). In 'the apple, where auxins are generadlly inactive, the giibberellins induce parthenocarpy and sustain fruit growth to maturity (2,6,10). This pronounced fruit-setting activity and the established observation -that asymmetric growth of apple fruit is related to incomplete seed development, has encouraged investigations on the relationship of endogenous seed gibberellins to fruit-set and growth. Gibiberellin-like activity ihas been demonstrated in endosperm (11) and GA4 and GA7 iden'tilfied in immature apple 'seed (8). The biosynthesis of gibberellins by 'seeds is viewed as a specific role of seeds in fruit-set of the apple (7). However, some cultivars of Malus are prone to produce seedless fruit after exposure to 'low temperature during the fruit-setting period. The presence of giibberellinlile substances in such parthenocarpic fruit is, herein, reported. Immature seedless apple fruits (Malus sylvestris Mill., selectiion New Jersey 12) developing subsequent to a severe 'frost, 4 days after full bloom, were -harvested (6-wk post-'bloom), frozen immedi;ately and stored at -30? until' used. Frozen fruits (6.9 kg) were immersed in 100 % acetone (7.6 -liters), then each fruit was halved to check for seedlessness (no seeds were found), homogenized 'in acetone and extracted twice by stirring under nitr-ogen for 24 hours at 2?. The filtrates were combined and concentrated to an aqueous solution (3.5,1iters, pH of 2.8) in vacuo. The pH of the filtrate was increased to 6.0 with 10 % KOH !(13) and centrifuged to remove proteins and other insoluble substances. The supernate was washed with n-hexane and adjusted to pH 2.0, stirred for 2 hours aifter aiddition of 70 g of activated charcoal and filtered. The charcoal was washed several times with distilled water and eluted with acetone. The eluate (acetone) was evaporated ito dryness, the residue (2.62 g) suispended in phosphate buffer (0.2 M, pH 6.2) and extracted with chloroform (9). The aqueous phase was adjusted ,to pH 2.5 with suilfuric acid and extracted with ethyl acetate. The chlorofom and ethyl aicetate extracts were dried over anhydrous sodium sulfate and evaporated to dryness yielding residues of 0.108 and 0.690 g, respectively. Tihese residues were taken ,up in ethanol and lanolin paste preparations of either fraction were found to induce parthenocarpy in tomato. The chloroform fraction was more active than the ethyl acetate fraction. Considerable quantities of inhibitors we-re present in the ethyl acetate fraction as was evidenced by injury of treated ovaries. Further puriification was aohieved by streaking the extracts on Whatman 3 MM paper (57 X 46 am) and developing with isopropanol :ammonium hydroxide:water (10:1:1 v/v). The chromatograms were cut transversely, at intervailis of 0.1 RF, and eluted with 80 % ethanod. The gi;bberellin aictivity of each eluate was assessed uising dwarf pea (9) (cv. Morse's Progress No. 9) and eticutmber seedling (4) (cv. Burpee Hybrid) assays. The chloroform fraction contained an active component(s) migrating to RF 0.4 to 0.7 and which was similar in activity and RF with authentic GA. treated tinder identical conditions (fig 1). A greater quantitative response was obtained from the chloroform than ethyl acetate fraction (approx 10-folld) in the dwarf pea assay. Little or no activity was observed for both fractions in the cucumber assay. Further purification was limited to the active component(s) of the chloroform fraction migrating to RF 0.4 to 0.7. The eluate was streaked on silica gel-G plates (E. Merck F-254, 250 p). Plates were developed with the lower phase of carbon tetrachloride :acetic acid :water (8:3 :5, v/v) plus 20 % ethyl acetate. The active component(s) did not migrate, thtus it was elluted from the origin with ethanol and rechromatographed tusing benzene: n-'butanol :acetic acid (70:25 :5 v/v) as the developing solvent. The active component(s) was identical to GA1 and/or GA3 with respect to RF (0.54) and color of filtorescence and differed in both respects 1 Michigan Agricultural Experiment Station Journal Article No. 4227.

Occurrence of Gibberellin A3 in Parthenocarpic Apple Fruit

Occurrence of Gibberellin A₃ in Parthenocarpic Apple Fruit