Ethylene and the control of axillary bud growth in Phaseolus vulgaris L

Yeang, Hoong Yeet (1980) Ethylene and the control of axillary bud growth in Phaseolus vulgaris L. PhD thesis, University of Glasgow.

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Abstract

This thesis is concerned with investigations into the involvement of ethylene in the control of axillary bud growth in Phaseolus vulgaris L. Ancillary studies on the characteristics of axillary bud outgrowth and on the methodology of quantitative ethylene analyses were also carried out. Growth of the leaves, internodes and axillary buds of intact young Phaseolus plants was governed by a fine degree of correlative control. The 1st trifoliate axillary bud, which was the bud studied in most of the experiments, showed slow but continuous growth at the time the plants were used for experiments (19 - 29 days old). Decapitation of the plant at the 3rd internode induced vigorous growth of this bud. The time lag between the decapitation stimulus and the detection of increased growth, determined by a photographic technique, was found to be 3-5 h. Much of the initial increase in the length of the bud internode may be attributed to cell expansion. Vascular transport to axillary buds was investigated using decolorised basic fuchsin as a tracer. The results indicate that functional xylem continuity was already well established between the stem and the inhibited buds. The lack of vascular supply was not, therefore, the cause of growth inhibition. Phloem transport was not studied directly, but free lateral transport of radioactivity from labelled sucrose from the xylem to the more peripheral tissues was demonstrated. The internal gaseous content of Phaseolus shoot tissue was sampled by vacuum extraction. The identities of ethylene and ethane in the gaseous extracts of apical shoots were established conclusively by a GC-MS selective ion detection method. Changes in the volume and composition of the gases recovered were observed when the evacuation conditions during extraction were altered. These changes were different in the primary leaves and in the 2nd trifoliate leaves. Thus, estimates of internal ethylene and ethane concentrations in plant tissues were influenced by the morphology of the tissue and the evacuation conditions employed. The internal ethylene concentrations in the primary, 1st trifoliate and 2nd trifoliate leaves, considered together, were correlated to their respective rates of ethylene emanation. Only trace emanation of ethane was recorded. Physical confinement of the developing apical shoot inhibited its growth and promoted the growth of axillary buds located basipetal to the treated portion of the shoot. These developments were thought to be brought about by ethylene since (a) the internal ethylene concentration and the rate of ethylene emanation were significantly increased in the treated tissue and (b) similar responses in shoot inhibition and axillary bud outgrowth were observed on plants with apical shoots treated with ethephon or ethylene. There is evidence to suggest that the promotion of axillary bud development by ethylene action on the apical shoot was associated with the availability of freely diffusible ethylene in the tissues of the treated shoot. Loss of apical dominance was not, apparently, directly dependent on either the internal ethylene concentration (i.e. concentration in the vacuum-extracted gases) or on the rate of ethylene emanation. Although treatment of the shoot with tri-iodobenzoic acid (TIBA) induced various morphological responses in the plant, including axillary bud outgrowth, which appeared similar to the responses to ethylene, the initial effect of TIBA is not thought to be ethylene-mediated. Applications of ethephon or ethylene inhibitors - Ag+ or aminoethoxy-vinyl glycine (AVG) - directly to the axillary buds of the intact plant were ineffective in eliciting bud development. When applied in appropriate dosages to the axillary bud of the decapitated plant, ethephon or ethylene inhibitors inhibited the outgrowth of the released bud. The general conclusion that may be drawn from these observations is that ethylene is essential in maintaining normal axillary bud growth in the decapitated plant, but the absence of bud development in the intact plant is not due to a lack of free ethylene. (Abstract shortened by ProQuest.).

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J R Hillman
Keywords: Plant sciences
Date of Award: 1980
Depositing User: Enlighten Team
Unique ID: glathesis:1980-71973
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 May 2019 13:34
Last Modified: 17 May 2019 13:34
URI: http://theses.gla.ac.uk/id/eprint/71973

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