Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and

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1 Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author.

2 I. THE EFFECTS OF DEFULIATION AND SHADING ON ROOT GROWTH OF LOLIUK PERENNE L. A thesis submitted for the degree of Dootor of Philosophy to Massey University P. s. Evans 1971

3 II. ABSTRACT The effects of defoliation, shading and dark on the growth and morphology of roots of Lolium perenne L. plants have been examined using glass tronted containers and a technique developed for measur ing root lengths and numbers of apices. single defoliation caused a rapid drop in root elongation followed b7 a more gradual recovery with the most severe defoliation treatment having the greatest effect. Repeated defoliation caused a prolonged depression of root elongation but some recovery occurred. The most severe treatment resulted in considerable root death. With shading, root elongation fell over the first 8 10 days and then rec overed to near the control level. Both defoliation and shading caused an increase in the length per unit weight of the root systems. Root elonga ion of plants placed in the dark fell rapidly to near zero, the effect being comparable with that of defoliating plants to 2.5 om or less. Defoliation of plants placed in the dark caused a more rapid fall in elongation. A Supplying glucose or sucrose to the roots of plants defoliated to the extent that root elongation would otherwise have ceased main tained elongation at up to twothirds of the level of undefoliated plants. Sucrose was marginal ly more effective than glucose with little difference between concentrations 16. Benzyladenine and indoleaceticacid marginally increased elongation in the presence of sucrose. Darktreated plants responded in a similar mann er to defoliated plants to sucrose. The level of soluble carbohydrates in the roots of plants defoliated or pl aced in the dark was seen to be low after root elongation ceased and recovered as root elongation recovered. However the level at the time.most roots ceased elongating was higher than in other experiments where root elongation was near optimum. That under these conditions the addition of sucrose or gluc ose maintains elongation at up to twothirds of the control level sug gests that translocation of soluble carbohydrates to the root apex m&7 be the limiting factor. This possibility is supported by the differ ence in levels of soluble carbohydrates in various parts of the plant following defoliation at two different times of the day. The tech

4 III. nique used to measure soluble carbohydrates was not sensitive enough to permit analysis of the root tips and thus oheck the hypothesis. Apart from the requirement for soluble carbohydrates and the apparent associated translocation factor there is evidentl7 some other factor {s ) limiting root elongation of defoliated and darktr ats plants. The nature of this factor was not determined

5 \. rv. ACKNOWLEDGEMENTS The guidance of Professor R. G. Thomas and Dr. E. D. Perm,y, Bo"tany Department is gratefully acknowledged. Appreciation is expressed to Mr. v. J. Thomas, Applied Mathematics Division, D.S.I.R., for helpful discussion and to Mr. P. DUks and Mr. M. H. Olsen for technical assistance. The fa cilities for this at were provided by Graaslands Division, D.S.I.R.

6 V TABLE OF CONTENTS PAGE 1 INTRODUCTION 2 MATERIALS AND JWrHODS Introduction Choice of experimental material Parameters studied and methods used 5 3 EFFECTS OF DEFOLIATION AND SHADING ON ROOT GROW'm ). 1 Introduction 3. 2 Effeot of a single defoliation Effect of repeated defol iation Effect of shading 3 5 Discussion 4 7 OF DEFOLIATION ABD SHADING EFFECTS LITERATURE MECHANISM 4 1 Introduction 4. 2 Carbohydrate levels in roots Importance of substances other than carbohydrates Excised root a tud i es 21 5 RESPONSE TO SUGAR IN DEJULIA'l'ED PLANTS 5.1 Introduction Effect of glucose Comparision of gl \cose and suorose as nergj souroea Optimum sucrose level Response to sucrose a:t several defoliation levels Discussion 6 EFFECT OF GROWTH SUBSTANCES 6. 1 Preliminary experiment 6. 2 Effect of benzyladenine without sucrose

7 CHAPTER PAGE 6.3 Optimttm benzyladenine concentration 6.4 Effect of gibberellic acid Effect of indole acetic acid Combinations of benzyladenine and other substances Di scussion 7 GROWTH IN THE 40 DARK 7. 1 Introduction 7.2 Growth at constant temperature 7 3 Effect of dark and return to light Time course of growth depression 7 5 Effect of s ucros e in the dark Effect of defoliation on darkplussucrose treated pl ants Effect of low intensity light Discussion 50 8 SOLUBLE CARBOHYDRATE 8.1 Introduction LEVELS, 8.2 Effect of a single defoliation 8.3 Effect of dark Soluble carbohydrate movement following defoliation DisouAsion 9 CHANGES IN '!HE ROOT 9.1 Introduction APEX 9.2 Effect of defol iation on the root apex Cell l engt h depression in roots o f dark treated plants D i s cus s ion 10 DISCUSSION APPENDIX PAGE 1 Measurement of total root length and apex numbers 2 Glass tronted containers 3 Effect of nutrient concentration

8 m APPENDIX 4 Effect of temperature PAGE Development of young plants 86 Effect of seed weight on plant size 89 Trial planting of glass frontad containers 91 Root diameter and growth rates 92 The effect of one per cent glucose on seedling root growth Application of glucose to individual roots Effect of indole acetic acid on seminal root growth Effect of benzyladenine on root growth Effect of gibberellic acid on root growth Soluble carbohydrate analysis Trial washing of roots BIBLIOGRAPHY 103 PAPER PUBLISHED ON PRELIMINARY S'ruDIES.

9 nn LIST OF FIGURES FIGURE FULLOWING 1 Singl e defoliation on root elongation 2 Repeated defol iation on root elongation 3 Three levels of shading on root elongation Response of defol iated pl ants to glucose Comparison of sucrose and glucose on root elongation Two sucrose levels on defoliated and undefoliated plants Four sucrose levels on defoliated pl ants 8 Effect of sucrose at two defoliation levels 9 Effect of sucrose on laxly defoliated plants Four defoliation levels on sucrosetreated plants Combinations of growth substances prelimidary experiment 6 PAGE Effect o f benzyl adenine without sucrose 13 Four benzyl adenine concentrations with sucrose Effect of four gibberellic acid concentrations Effect of four indole aoetic acid concentrations 16 Combinations of benzyladenine and other growth substanoes 3 '? Four hour root elongation at constant temperature 18 Response to placing planta in dark to light and 43 returning Fall in root elongalion on defoliating or plao1ng 1n dark Effect of sucrose on plants in dark Defol iation on plants supplied sucrose in dark 22 Low 24 Fall in root elongationj effect of low intensit7 light 50 Effect of defoliation on cell l ength pattern oortu intensity l ight on pl ants supplied sucrose Comparison of high light, low light and dark of root., 26 Effeot of defoliation and dark on cell length in mature cortex tissue 64

10 If LIS'!' OF 'l'ables TABLE FOLLOWING PAGE 1 Effect of a single defoliation on plant size 10 2 Etfeot of repeated defoliation on root morphology 11 3 Effect of shading on root morphology 14 4 Soluble carbohydrates and root elongation of defoliated plants 53 5 Level of soluble carbohydrates in roots of plants supplied with sucrose 55 6 Effect of dark and return to light on soluble carbohydrates in roots 56 1 Level of soluble carbohydrates in roots of plants supplied with sucrose 1D dark 57 8 Level of soluble carbohydrates in roots and shoots of plants defoliated to two levels at different times 59