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  • Author or Editor: Loyd E. Powell x
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Abstract

The analysis of plant extracts or diffusates for hormones has always bordered on the mysterious, and has been fraught with pitfalls for even determined investigators. Many of the problems have arisen from the exceedingly low concentrations in which hormones generally occur, and which consequently have necessitated the employment of bioassays. In recent years improved instrumentation has made it increasingly feasible to employ physical methods for detection and measurement of these substances. The options available are confusing, particularly to those new to the field. It is the purpose of this brief review to put in perspective the various methods available to an investigator, and to elaborate on the direction we seem to be moving.

Open Access
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Abstract

Seedlings of Malus hupehensis Rehd., M. domestica Borkh. cv. Northern Spy and Betula papyrifera Marsh were grown under short and long photoperiods, with other environmental conditions being similar. M. hupehensis seedlings stopped elongation under short days (SD) and continued growth under long days (LD). There was no significant difference in abscisic acid (ABA) content in shoot tips taken from seedlings under either photoperiod. ‘Northern Spy’ seedlings ceased growth under SD, but neither did they grow vigorously under LD. Shoot tips of these seedlings were not significantly higher in ABA content when grown under SD. Betula seedlings discontinued elongation under short photoperiods, while LD promoted growth. Betula shoot tips from LD seedlings had more ABA than from seedlings grown under SD. These data do not support the hypothesis that SD causes cessation of shoot elongation by inducing a build up of ABA.

Open Access

Abstract

Abscisic acid (ABA) inhibited bud break and shoot elongation in seedling stem explants of apple (Malus domestica Borkh cv. Northern Spy) cultured in vitro. Inhibition was complete in culture medium containing 100 μM ABA. Transfer of buds from ABA-containing medium to basal medium resulted in increases in both bud break and shoot elongation. ABA levels in such buds declined rapidly following transfer, and growth began when ABA concentration in the buds dropped below a threshold value.

Open Access

Abstract

Axillary buds from apple shoots when cultured aseptically in vitro readily develop into new shoots. A nutrient medium is used consisting of sucrose and macro and micro elements. Buds grown in stationary culture develop into shoots with small leaves and short internodes. The miniature condition appears to be due to inability of the rootless explants to absorb sufficient nutrients. When buds are cultured in rotating culture where the developing leaves are bathed in nutrient solution, shoots of near normal size and appearance are produced. Light is essential for growth. Low concn of abscisic acid prevents growth of the buds.

Open Access

Abstract

The growth of excised grape shoots in the absence of roots was investigated using asceptic culture. Sustained shoot development was observed only when cytokinins were present in the media. We used ‘Concord’ (Vitis labruscana Bailey) in most experiments, but the response was observed in other cultivars including those of Vitis vinifera L. Better response was obtained with cytokinin ribosides than with free bases. If roots developed, the requirement for an exogenous source of cytokinin was nullified.

Open Access

Abstract

Endogenous abscisic acid (ABA) decreased during chilling in buds of several cultivars of Vitis vinifera L., Vitis riparia Michx. and Vitis labruscana Bailey, both in field grown and greenhouse vines. During bud burst, ABA decreased on a concentration basis only, until just prior to leaf unfolding. Bud scale removal hastened bud burst. Although ABA content was higher in scales than in primordia, changes in ABA level during chilling and bud burst occurred only in primordia. Lateral buds, which are committed to grow the year of formation, had higher ABA levels than dormant axillary buds which require a chilling period to grow. Applications of ABA, gibberellic acid (GA3), and (2-chloroethyl)trimethylammonium chloride (CCC) to dormant, chilled grape cuttings had no effect on time to burst, while zeatin hastened burst. These results suggest that, if there is an interaction between chilling and ABA, it is of secondary importance in bud burst of grape.

Open Access

Abstract

When apple (Malus sylvestris Mill) seedlings are fed abscisic acid (ABA), a water soluble complex of ABA and glucose is rapidly formed. This may be a mechanism for inactivating ABA. Similarly, the trans isomer of ABA (trans-ABA) gives rise to a water soluble complex, which is also presumed to be a glucose complex. Apple seedlings did not convert ABA to trans-ABA during feeding experiments, suggesting that small amounts of trans-ABA occasionally found in apple seedling extracts may be artifacts.

Open Access

Abstract

Removal of bud scales hastened bud burst of several early and late blooming apple cultivars. Descaling was most effective during the onset and end of rest. During deep rest, bud scale removal was effective only when applied 2 weeks before forcing conditions. Extracts of bud scales inhibited apple bud break in vitro. Abscisic acid (ABA) may have been responsible for part or all of this bioactivity, since ABA occurred in bud scale diffusates and could replace or reinforce the bud scales in vitro. Wound-produced ethylene was not involved in the bud scale removal response.

Open Access