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Title: Fluctuations in the endogenous abscisic acid content of Alnus glutinosa (L.) Gaertn
Author: Watts, Susan H.
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1985
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Abstract:
This thesis concerns an investigation of the distribution of the plant growth substance abscisic acid (ABA) in the deciduous tree Alnus glutinosa (L. ) Gaertn. , a species which bears nitrogen-fixing root nodules. The study was divided into two areas: (i) the identification and quantification of endogenous ABA in Alnus (ii) the transport of applied [2-14C] ABA; results are presented in two sections accordingly. In part 1.1 of the Results, the development of a schema suitable for the purification of ABA from Alnus tissues is described. ABA was successfully identified in Alnus roots, leaves and nodules using the technique of combined gas-chromatography/mass-spectrometry (GCMS ); this is the first report of the occurrence of ABA in perennial root nodules. Routine quantification of ABA in extracts was by gas-chromatrography using an electron-capture detector (GCECD ) ; all extracts incorporated an internal [2-14C] ABA standard to correct for purification losses, and further checks of the methods employed were made. The variation in plant root, leaf and nodule ABA content was investigated in greenhouse-grown plants, and it was demonstrated that whilst there were significant differences in the 'total' ('free' plus 'bound') ABA content of all three tissues, and between the 'free' ABA content of the leaves and the roots/ nodules (but not between the roots and the nodules) there were no significant differences in the 'free', 'total' or 'bound' ABA content of replicate batches of 20 plants each. In part 1.2 of the Results, experiments involving the quantification of endogenous ABA in Alnus are described. An investigation of seasonal fluctuations in nodule 'free' ABA levels in plants growing under natural photoperiod but frost-free conditions was made in 1980/1981, and correlated with seasonal changes in nodule nitrogenase activity (acetylene reduction). There was no clear relationship between nodule ABA content (which ranged from 101 - 879ng g 1 f. wt in this season) and the onset of nitrogen fixation in March after winter dormancy, although there was a broad inverse correlation between rates of nodule acetylene reduction and nodule ABA levels in this season. The possibility of diurnal fluctuations in leaf and nodule ABA content was next examined in greenhouse-and growth-room-grown plants. Careful analyses of 'free' and 'bound' cis and trans ABA levels failed to demonstrate any fluctuations in leaf or nodule ABA content over a 24h period. Root-applied 0.1mol m-3 synthetic (+) ABA led to increased endogenous ABA levels and to the onset of bud dormancy in plants growing in water culture in long day conditions. In part 2 of the Results, the translocation of radioactivity and ABA following [2-14C] ABA application is described. In plants grown under short photoperiods for at least 34 d, less radioactivity was translocated out of the donor leaf 24h following [2-14C] ABA application than in long-day conditions and of that translocated, at least 3 times more was recovered in the tissues below the site of application than above it. In plants grown under long days, at least as much C was transported acropetally as to tissues underlying the donor leaf. TLC of tissue extracts following petiolar [2-14C] ABA application demonstrated that [2-14C] ABA distribution was similar to that of 14C m plants growing under both long and short photoperiods. However, [2- 14C] ABA levels (expressed as a percentage of the radioactivity present) in the stem and leaf tissues beneath the donor leaf were up to 12. 6 and 5.9 times greater respectively in short-day treated plants than those observed in plants grown under long days, illustrating the influence of photoperiod on tissue ABA metabolism. Experiments described in 2.1.4 indicated that ABA is phloem-translocated in Alnus shoots, although phloem s xylem exchange may occur in the root system. Finally, in section 2.2 of the Results, the translocation of radioactivity and ethyl-acetate-soluble radioactivity following root [2-14C] ABA application for 5d to young plants growing in water culture is described. In the presence of 2.52 x 10-5mol m-3 [2-14C] ABA, 6.3 % of the total ABA available in the culture solution was taken-up by the plants (assuming that all of the radioactivity recovered in the plants entered the root system as [2-14C] ABA). Uptake of [2-14C] ABA represented only 2.3 - 2.6 % of the total synthetic ABA available to plants in root-contact with 0.1mol m-3 synthetic ABA 'spiked' with [2-14C] ABA. The implications of the results described in this thesis are considered in the Discussion which also highlights the problems encountered, and possible directions for further research concerning plant growth substances.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.795794  DOI: Not available
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