Bending stress resulted in an increase in the ethylene concentration in the internal atmosphere of apple stems {Malus domestica Borkh. cv. Winesap), reaching a maximum at about 2 days after bending. The rise in ethylene content was followed by a depression of growth at about 14-21 days. Ethylene content returned to control levels after about 3 weeks. Application of a paste of naphthaleneacetic acid caused a similar increase in ethylene levels, and the application of ethephon pastes brought about an inhibition of elongation growth. Whereas stress treatment resulted in an inhibition of growth in stem diameter as well as elongation, the ethephon applications resulted in a stimulation of growth in diameter. It is suggested that ethylene may be involved in the growth responses to mechanical stress.
Buds of ‘Golden Delicious’ apple (Malus domestica Borkh.) were in deep rest between October 25 and December 20, 1976, although the uppermost bud on decapitated (apical and basal cuts) shoot segments developed at all sampling dates. Increases in rate of development of the uppermost bud, as well as in % break of lower buds after completion of deep rest, were both linear with time. Increases in % budbreak with time occurred in a basipetal direction, suggesting a gradient of increasingly deep rest from shoot apex to base. Development of the uppermost bud on decapitated shoots during deep rest was a result of the apical cut, and was not influenced by the original position of that bud on the intact shoot. The bud above the basal cut developed only on shoots with the terminal bud intact (basal cut only). Notching above a second bud on decapitated shoots did cause that bud to develop in addition to the uppermost bud. Results are discussed on the basis of a 2 stage rest model, rest gradient and apical dominance. There was no evidence for a role of ethylene in wounding or dinitro-orthocresol-stimulated budbreak. In addition, neither ethylene-releasing chemicals nor silver or cobalt had any influence on budbreak when applied to shoots at 2 dates during the rest period.
Floral tissue of dormant sour cherry (Prunus cerasus L.) flower buds was examined by light and electron microscopy during field development and laboratory chilling. Differentiation of flower parts ceased by early November and there was no further morphological development until visible signs of budbreak occurred after the end of rest. Pollen meiosis occurred at the half green budbreak stage. No ultrastructural changes accompanied chilling accumulation except development of numerous starch grains in plastids. Buds on cut shoots held at the non‐chilling temperature of 15 C developed more mitochondria but acquired no starch when compared with buds on cut shoots held at a 5 C chilling temperature. Nuclei and nucleoli enlarged with chilling in ovules and sporogenous cells but not in ovary parenchyma. Accumulation of starch with chilling in most bud tissues was demonstrated histochemically.
Increases in internal ethylene concentrations occurred after attached and detached apple (Malus domestica, Borkh. cv. Winesap) shoots were placed in a horizontal position. Ethylene was higher in the underside of the shoot, and decreased linearly in a basipetal direction along the axis. Bent and horizontally-oriented detached shoots did not increase in ethylene at 20°C, but increased to identical levels at 30°, suggesting that responses to the 2 types of stress were identical. Although gravitational stress alone increased ethylene levels, an experiment designed to separate bending stress from gravitational stress was inconclusive because rotation decreased shoot ethylene levels.
(4,7, 26). In apple, the optimum conditions for stratification, or after-ripening as it is often called (14), are exposure to 5°C (14) for approximately 60 d (17).The actual mechanism of low temperature release from dormancy is not known. One hypothesis is that ABA functions as a germination inhibitor and GA3 functions as a germination promoter, and the degree or depth of dormancy is a result of the ratio of the two (2, 24). GA3 levels increase during stratification (24). In hazel seeds, exogenous application of GA3 substitutes for stratification. Following such application, RNA synthesis increases as a result of increased RNA polymerase activity and DNA template availability (8, 9) indicating that release from dormancy involves gene expression (25). Excised pear embryos synthesize nucleic acids due to stratification without GA3 application (12). Application of ABA to pear embryos decreases synthesis of specific RNA fractions (11) and changes the embryo's nucleotide composition (10). While the in vitro translational capacity of polyribosomes ' Journal Paper No. 9192 of the Purdue University Agricultural Experiment Station. This paper is part of the M.S. thesis of D. A. E.
Hendricks (6) concluded that the promotive action of CNon lettuce-seed germination was nutritional, resulting from incorporation of cyanide into amino acids and protein. Yentur and Leopold (8) showed that seed respiration of various species was CN--resistant at early stages of germination but became CN--sensitive at later stages. Lettuce seed germination in the presence of CN-has been found to proceed normally, even if seeds were imbibed directly in solutions containing 10 mm KCN (9).A common technique utilized in many previous germination studies was to incubate seeds in covered Petri dishes. However, it has been observed during experiments in our laboratory that, if covered Petri dishes containing lettuce seeds imbibed in KCN were sealed with thermoplastic film to prevent desiccation during long incubations, germination was blocked even at very low levels of KCN. Since preliminary observations suggested that inhibited germination was not the result of sealing per se (ie. in the absence of KCN), the apparent cyanide effect was investigated further. Alkali Traps in Closed Systems. A 1.2-cm-diameter plastic vial cap was inverted in the center of each dish as a centerwell, and 0.1 ml of either H20 or 3.6 N KOH was added before sealing with Parafilm. Seeds were imbibed directly in 1.2 ml test solution consisting of either H20 or various concentrations of KCN. The alkali trap served to scavenge volatile acidic substances that otherwise would tend to accumulate within a sealed container.Generation of HCN within Closed Systems. Seeds were imbibed in 1.2 ml H20 instead of in KCN, but 0. l-ml aliquots of KCN at various concentrations were added to a centerwell. Dishes were immediately sealed with Parafilm, and 0.1 ml I N H2SO4 was injected into the centerwell through a tape-sealed pinhole in the cover of the dish. The hole was immediately resealed with tape.Exogenous HCN. HCN gas was generated separately by injecting 0.6 ml 10 N H2S04 into a sealed 50-ml Erlenmeyer flask containing 0.3 ml 1 N KCN. The generation flask was maintained at 50 C with stirring. HCN gas distilled through a sidearm connection to a collection flask containing 30 ml H20 held at ice temperature. After 24 h of incubation, aliquots of the collecting solution were withdrawn by syringe through a serum stopper, and cyanide was determined colorimetrically, according to the method of Robbie and Leinfelder (5). Once determined, precise volumes of aqueous HCN were removed and injected into sealed Petri dishes, either directly or after further dilution. This procedure permitted control of the dosage of HCN delivered to, and potentially available for, interaction with the enclosed seeds.Cyanide Reversibility. Seeds were incubated as described, either in H20 or in 3 mm KCN, within sealed Petri dishes. Seals were removed after 3 days, and seeds were maintained in test solutions for an additional 4 days. Germination was evaluated daily under green safelight without disturbing incubation conditions. Species Survey of Cyanide Sensitivity. Seeds of nine additi...
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