Hormone transport in relation to geotropism in Zea mays and Helianthus annuus seedlings

Webster, Janet Hilary (1977) Hormone transport in relation to geotropism in Zea mays and Helianthus annuus seedlings. PhD thesis, University of Glasgow.

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Abstract

The possible involvement of gibberellins in the geotropic response of roots and shoots has been investigated using intact seedlings of Zea mays and Nelianthus annuus. The characteristics of the transport and metabolism of oxogenously applied (14C) GA, and (3H) GA, within the plant, has been examined using the classical agar donor block method for segments of plant tissue and the more precise micropipette technique for whole plants. With agar donor blocks, very little longitudinal movement of radioactivity from (14C) GA, was found to occur in Zea coleoptile segments and even after transport periods of 24 h, there was virtually no movement of radioactivity into agar receiver blocks at either the apical or basal end of the segment. The application of a pulse of (14C) GA3, as an aqueous solution in a micropipette, to excised intact coleoptile apices confirmed that there was no obvious longitudinal polarity and no movement of radioactivity into receiver blocks. Similarly the application of a pulse of (14C) GA, to geotropically stimulated roots of intact Zea seedlings, resulted in a very limited capacity for both acropetal and basipetal movement. Most of the radioactivity remained adjacent to the original point of application, even after 12 h transport periods. Lateral transport studies, whereby a pulse of either (14C) GA3 or (3H) GA, was applied to roots and shoots of horizontally and vertically orientated Zea seedlings, confirmed the minimal longitudinal movement of radioactivity. However, a significant net upward lateral movement of radioactivity from (14C) GA3 was found to occur in both roots and shoots of Zea seedlings that were geotropically stimulated. No lateral redistribution of radioactivity from (3H) GA, was found to occur in either Zea roots or shoots. Little metabolism of either (14C) GA3 or (3H) GA1 occurred in either Zea roots or shoots and it was a apparent that the translocation pattern of radioactivity in these organs reflected that of gibberellin. Experiments using intact Helianthus seedlings showed a very slight acropetal movement although much of the radioactivity remained in the region of application. No enhanced lateral redistribution of radioactivity was observed in either epicotyls or hypocotyls, as a result of prolonged geotropic stimulation. Attempts were made to determine whether gibberellins were present naturally in the shoot apices of both Zea and Helianthus seedlings and if so, whether they might undergo lateral redistribution or differential synthesis or release as a result of geotropic stimulation. The classical techniques of extraction, collection in agar and bioassay were employed. Extensive experimentation confirmed the presence of endogenous gibberellins in Helianthus shoot apices but failed to demonstrate their existence in Zea coleoptiles.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Malcolm B Wilkins
Keywords: Plant sciences
Date of Award: 1977
Depositing User: Enlighten Team
Unique ID: glathesis:1977-72803
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: http://theses.gla.ac.uk/id/eprint/72803

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