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  • Author or Editor: F.G. Dennis Jr. x
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Abstract

Went and Thimann (50) defined a hormone as ‘a substance which, being produced in one part of an organism, is transferred to another part and there influences a specific physiological process.’ In the strict sense of the word, growth substances extracted from plant tissues cannot be called hormones. In this paper, however, the term will be used in a general sense to refer to auxins, gibberellins (GAs), cytokinins, inhibitors, and ethylene occurring in plant extracts, diffusates, exuded sap, or intercellular spaces.

Open Access

Abstract

Production of temperate-zone fruits in the tropics and subtropics may seem fanciful to the uninitiated, but it is a practice that has existed in localized regions for generations. Seedling peaches are grown in Venezuela (7), northern Thailand (11), and southern Mexico (5). No one knows precisely when these species were introduced, but local selection has produced cultivars adapted to areas with little or no chilling temperatures. Rest either does not occur (5) or is sufficiently shallow to be broken by stress induced by defoliation or drought.

Open Access

Abstract

Growth inhibitors have been implicated in the control of many physiological processes, including dormancy of seeds and buds (35, 36, 45), apical dominance (43), root initiation (12), flowering (13, 16, 44), abscission (5, 8, 25), fruit development (11), dwarfism (29, 40, 50) and senescence (26). Despite the abundance of correlative evidence obtained, no cases are known in which irrefutable proof exists for such control. The purpose of this paper is to discuss how correlations may be extended to proof of a causal relationship. For convenience, most of the illustrations will be drawn from studies of seed and bud dormancy.

Open Access

Abstract

Fall applications of several chemicals were evaluated for their effects in delaying bloom of tree fruits. Sprays of gibberellic acid (KGA3) had no effect on time of bloom of sour cherry (Prunus cerasus L.) or sweet cherry (Prunus avium L.) but resulted in moderate to severe winter injury to the cambium and flower buds of the latter. Neither succinic acid-2,2-dimethylhydrazide (SADH) nor α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol) had observable effects on sour cherry, apple (Malus domestica Bork.), or apricot (Prunus armeniaca L.). (2-Chloroethyl)phosphonic acid (ethephon) delayed bloom in several stone fruits, including sweet cherry and plum (Prunus domestica L.), and thereby reduced spring freeze injury. Beneficial effects were offset, however, by deleterious side effects such as gummosis, bud abscission or failure to open, and reduced fruit set.

Open Access

Abstract

Gibberellin (GA)-like substances in extracts of immature apple (Malus domestica Borkh.) seeds and fruits were partially purified by paper and column chromatography. Following silicic acid column chromatography, two zones of activity (S-I and S-II) were observed in seed extracts, occurring at the approximate elution volumes of GA4/7 and GA5/6 respectively. On thin layer chromatograms, most of the biological activity of S-I occurred at the Rf of GA4/7, although an additional less polar GA-like component appeared to be present; that of S-II occurred at the Rf of GA3. Both S-I and S-II were active in all 5 bioassays used. Levels of both components were at a maximum in early July, shortly after June drop. Bioassay of extracts prepared at this time indicated that over 95% of the activity occurred in the endosperm. Extracts of fruit flesh contained two GA-like components, both more polar than GA4/7. Activity per unit fresh weight was approximately 3000 fold higher in seeds than in fruit tissue. The possible roles of these compounds in fruit development and flowering are discussed.

Open Access

Abstract

Gibberellic acid (GA3) has little effect on fruit set in seeded commercial varieties of apple unless pollination is prevented. To determine whether seedless apples might respond to GA, blossoms of several apetalous clones were treated with gibberellins. In addition, seeded and seedless fruits were sprayed several weeks after bloom with naphthaleneacetic acid (NAA), a fruit-thinning agent, to ascertain the role of seeds in auxin-induced fruit abscission.

GA3 was effective in increasing fruit set in 2 of the 6 clones tested, but had no effect on the remaining 4, only one of which crops heavily under orchard conditions. GA7 and GA4+7 were more active than GA3 in inducing fruit set in the 2 responsive clones. NAA thinned both seeded and seedless fruits of one clone. Fruit growth was inhibited in seedless fruits of 2 other clones, but abscission was not promoted. These results support the view that NAA-induced fruit abscission is not a result of seed abortion.

Open Access

Exposure of stratified apple (Malus domestics Borkh. cv. Golden Delicious) seeds to 30C induces secondary dormancy. To determine if an increase in abscisic acid (ABA) content was associated with the loss in germination capacity, stratified seeds (3,- 6, or 9 weeks at 5C) were held at 30C for 0, 3, or 6 days. Stratification at 5C either had no effect or increased ABA content in embryonic axes, cotyledons, and seed coats. Exposure to 30C after stratification either did not affect or decreased ABA content of embryonic axes and seed coats; in contrast, cotyledonary ABA was increased. Seed coats, cotyledons, and embryonic axes stratified for 3, 6, or 9 weeks at 20C contained the same or higher levels of ABA in comparison with nonstratified seeds or seeds stratified at SC. Changes in ABA levels were not consistently correlated with changes in germination capacity during stratification or after exposure to 30C. These data suggest that changes in ABA are not related to changes in dormancy. Chemical names used: abscisic acid (ABA); butylated hydroxy-toluene (BHT); n-(trichloromethyl) thio-4-cyclohexene-1,2-dicarboximide(Captan).

Free access

Abstract

Parthenocarpy was induced in emasculated strawberry (Fragaria × ananassa Duch.) flowers with aqueous solutions of 10−3 M NAA, GA3 or GA4+7 in 2% DMSO plus 0.1% Tween 80. All fruit except those treated with NAA stopped growing within 12 days of treatment. Repeat application with NAA or GA4+7 20 days after initial treatment stimulated continued growth of NAA-induced fruit, but had little or no effect on growth of GA4+7-induced fruit. The diameters of mature parthenocarpic fruit ranged from 70% to 90% of that of pollinated fruit. Achene removal 12 days after pollination greatly reduced subsequent growth of receptacle tissue, complete removal being more effective than partial removal. Following achene removal 16 days after pollination, treatment with aqueous solutions of NAA in 2% DMSO and 0.1% Tween 80 produced receptacles 75% the size of controls with intact achenes, but neither GA3 nor GA4+7 stimulated growth. Achene removal 24 days after pollination did not influence further receptacle enlargement. Concentration of free indoleacetic acid (IAA) in NAA-treated fruit was 5-times that in controls and 3-times that in GA4+7-treated fruit 6 days after treatment. By 14 days after treatment, the levels had declined in all treated fruit. Free IAA concentration in the receptacle tissue of intact fruit was nearly equal to or greater than that in achenes 14 days after pollination. The growth rates of receptacles were positively correlated with numbers of intact achenes and free IAA content of the receptacle. Chemical names used: naphthaleneacetic acid (NAA); gibberellins (GA3 or GA4+7); dimethylsulfoxide (DMSO)

Open Access