Endogenous control of senescence in Pisum sativum L. (the garden pea)

Malik, Nasir Saeed Ahmed (1973) Endogenous control of senescence in Pisum sativum L. (the garden pea). PhD thesis, University of Glasgow.

Abstract

Early work of the 19th Century suggests that removal of flowers can delay senescence in annuals, an explanation of this phenomenon was not offered until Moliach published his results in 1928. He suggested that the fruit acts, as a sink for plant food reserves, from alternatives explanation wag given by Leopold et al. (1959) who showed that removal of flowers from male spinach plants and defruiting of complete fruits in bean can also delay senescence in them. Lockhart & Gottschall (1961) substantiated Leopold's work in peas. Wareing & Seth (1967), by applying hormones as a substitute for developing fruit, demonstrated a mobilization of nutrients to the site of hormone application. Two hypotheses exist to explain senescence of annuals and possibly in herbaceous biennials. (i) Imbalance in nutrient distribution in whole plant resulting in death of apical meristenis. (ii) Autonomous hormonal control. In the most extreme case this could be a specific senescence hormone. My work with peas has been designed to confirm the second hypothesis and can be divided into, three main headings. (i) Protein studies. (ii) Homone studies. (iii) Surgical experiments. Protein studies In explant studies a frequent correlation is made between proteins and the organ senescence. It was therefore attempted to study protein changes in relation to whole plant senescence, and at the same time try to find an objective method for measuring senescence in plants. Isoelectric focusing of proteins on acrylamide gels was carried out for separating proteins in this and a new staining technique was developed. It reduced the working time from days to hours and was then published. The results of these studies showed that changes appearing in leaf proteins were independent of flower or fruit development. It was easy to correlate aging in leaves with changes appearing in their proteins, but no correlations between leaf protein at any stage were possible with the aging of whole plant. (ii) Hormone studies Quantitative studies of endogenous GAs, ABA and cytokinins were started with a view to correlating their levels with plant senescence. Standard procedure of methanol extraction was followed to extract these, hormones. A new method was, however, developed for the initial group separation of GAs and ABA on alkylated sephadex. This column chromatography gave a very good initial purification of the group along with separation of inhibitors. Final purification and separation of individual GAs, ABA and also cytokinins were carried out on TLC, and the amounts were quantified on the basis of their biological activities. Results from these studies showed that flower and fruit development had very little effect on endogenous levels of leaf hormones as compared with their deflorated control. The maturity of fruits however brings distinct changes in leaf hormones. Studies on unknown inhibitors were left over, due to shortage of time. (iii) Surgical experiments Both, of the nutrient and hormonal explanations to plant senescence were offered from the observations obtained in different kinds of surgical experiments. This kind of experimentation, therefore appeared to be another interesting way for further investigations. Initially the effects of removing flowers, fruits, leaves and apices were studied both individually and in combinations. Later all experiments were conducted to separate the effects of fruit maturity from fruit filling. In these experiments initial observations wore taken in an experiment where branching was induced in the plants and then different numbers of pods were allowed to develop at different sites while continuously deflorating rest of the plant. Other experiments were then carried out using grafts. With this grafting technique it was possible to study the effects of fruit development and fruit maturity independently of each other. The main observation in these experiments was the growth of the younger part of the graft was affected by fruit when compared with corresponding defruited controls. Results obtained from these experiments were very conclusive and for the first time distinct effects of fruit maturity independent of fruit filling were demonstrated. Besides many interesting observations it was clearly shown that fruit development is a nutritional phenomenon but does not exhaust the plant for further growth, and fruit ripening produces a distinct dramatic stimulus that results in senescence of the meristematic region and so cancels any possibilities of further growth. It was then possible to demonstrate complete development of fruits consecutively for the three times on the same rook stock.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: A MM Berrie
• Keywords: Plant sciences
• Date of Award: 1973
• Depositing User: Enlighten Team
• Unique ID: glathesis:1973-73899
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73899