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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
I.
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 .
A 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.
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 two-thirds of the level of undefoliated plants. Sucrose was marginal ly more effective than glucose with little difference between concentrations 1-6�. Benzyladenine and indole-acetic-acid marginally increased elongation in the presence of sucrose. Dark-treated plants responded in a similar manner 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 two-thirds 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-
nique used to measure soluble carbohydrates was not sensitive enough to permit analysis of the root tips and thus oheck the
III .
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 dark-tr�ats� plants. The nature of this factor was not determined •
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ACKNOWLEDGEMENTS
The guidance of Professor R. G. Thomas and Dr. E . D . Perm,y , Bo"tany Department is gratefully aCknowledged. Appreciation is e xpressed 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 assist
ance . The facilities for this at� were provid ed by Graaslands Division , D . S . I . R .
TABLE OF CONTENTS
PAGE
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1 INTRODUCTION 1
2 MATERIALS AND JWrHODS
2 . 1 Introduction •••• • • • • • •• • ••••• • • • ••• •••• •• • • • • • •• 3 2 . 2 Choice of experimental material • • �••• • • •• • •• • ••• 4 2 . 3 Parameters studied and methods used •••••••••••••• 5
3 EFFECTS OF DEFOLIATION AND SHADING ON ROOT GROW'm
) . 1 Introduction • ••••••• • • • • • • • • • • • • • • • • •• • • • • • • • • • • 7 3.2 Effeot of a single defoliation •• • •••• • • •• • ••• • • • 9 3·3 Effect of repeated defoliation •••·••••• ••••• • • • •11 3·4 Effect of shading • • • • • • • • • •• • • ••• ••••• • • • • • • • • ••13 3•5 Discussion • •••••• • • • • • • • ••• • •• • •• • •• •• • • • •• •••••14 4 MECHANISM OF DEFOLIATION ABD SHADING EFFECTS
LITERATURE
4 • 1 Introduction •• • ••• • •• • •• • • • • • • •• • ••• • • • •• • • • • • ••18 4.2 Carbohydrate levels in roots ••• • ••• •• • ··�··• • • • •18 4 · 3 Importance of substances other than
carbohydrates •••• • •• • • ••• • • • •••20 4·4 Excised root atudies�••• • • • •• •• • • •• • • • • •• •• • • • • ••21
5 RESPONSE TO SUGAR IN DEJULIA'l'ED PLANTS
5.1 Introduction •• • ••• • • • • • • •• • • •• • • • •••• •• • • • • • • • • 23 5.2 Effect of glucose • • • •• • • • •• • • •• • • • • ••• • ••••• • •• 23 5·3 Comparision of gl•\cose and suorose as
nergJ souroea •••• ••• ••• • • • • • • 25 5·4 Optimum sucrose level • • • • • ••••• • • • • • •• • • ••• • • • • 26 5 · 5 Response to sucrose a:t several defoliation
levels • • ••• • • • ••••• •• • • • • • •• • • 29 5 . 6 Discussion •• ••• • · • •• • • • • • • • • • • • • •• • •• •••• • • • • • • 33
6 EFFECT OF GROWTH SUBSTANCES
6 . 1 Preliminary experiment • • • • • •• • • • • • • • • • • • • • • • • • • 34 6.2 Effect of benzyladenine without sucrose ••••••• • 35
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CHAPTER
6.3 Optimttm benzyladenine concentration •••••••••••
PAGE
36 6.4 Effect of gibberellic acid •••••••••••••••••••• 38 6 . 5 Effect of indole acetic acid ••••••••••••••• •• • 39 6.6 Combinations of benzyladenine and other
substances ••••••••••••••••••• 40 6.7 Discussion •••••••••• · • · • · ••••••••••••••• •••••• 40
7 GROWTH IN THE DARK
7 . 1 Introduction •••••••••• ••••••••••••••••••••••• 42 7.2 Growth at constant temperature •••••••••••••••• 42 7 ·3 Effect of dark and return to light •••••••••••• 43 7•4 Time course of growth depression •••••••••••••• 45 7•5 Effect of sucrose in the dark ••••••••••••••••• 46 7.6 Effect of defoliation on dark-plus-sucrose
-treated plants ••••••••••• •• • 47 1·1 Effect of low intensity light ••••••••••••••• •• 48 7.8 Discussion •••••• · · · ••••••••••••••••••••••••••• 50
8 SOLUBLE CARBOHYDRATE LEVELS
8.1 Introduction ••••••••••,••••••••••••••••••••••• 52 8.2 Effect of a single defoliation •••••••••••••••• 52 8.3 Effect of dark •••••••••• ••••••• ••••••••••••••• 55 8.4 Soluble carbohydrate movement following
defoliation •••••••••••••••••• 58 8.5 DisouAsion ••••• · · · •••••••••••••••••••••••••••• 60
9 CHANGES IN '!HE ROOT APEX
9.1 Introduction ••• • ••••••••• · • · •••••••••••••••••• 61 9.2 Effect of defoliation on the root apex •••••••• 6 1 9 · 3 Cell length depression in roots o f dark
-treated plants •••••••••••••• 65 9•4 Discussion •••••••••••• •••• •••••••••••••••••••• 65
1 0 DISCUSSION 68
APPENDIX PAGE
1 Measurement of total root length and apex numbers ••• 74 2 Glass tronted containers ••• ••••••• •••••••••••••••••• 77 3 Effect of nutrient concentration •••••••••••••••••••• 81
APPENDIX
4 Effect of temperature •••• • •••••••••••••••••••••••••••
PAGE 84 5
6 7 8 9
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 ••••••••••••••••••• 94 10 Application of glucose to individual roots ••••••••••• 96 11 Effect of indole acetic acid on seminal root growth •• 98 1 2 Effect of benzyladenine on root growth ••••••••••••••• 99 1 3 Effect of gibberellic acid on root growth ••••••••••••100 14 Soluble carbohydrate analysis ••••••••••••••••••••••••1 01 15 Trial washing of roots •••••••• •••••••••••••••••••••••1 02
BIBLIOGRAPHY ••• •••••••••••••••••••••••••••••••••••••••• •••••103 PAPER PUBLISHED ON PRELIMINARY S'ruDIES
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LIST OF FIGURES
FIGURE FULLOWING PAGE
1 Single defoliation on root elongation •••••••••••••••••••••10 2 Repeated defoliation on root elongation ••••••• ••••••••••••1 1 3 Three levels of shading on root elongation ••••••••••••••••1 3 4 Response of defol iated plants to glucose •••••••• ••••••••••24 5 Comparison of sucrose and glucose on root elongation •••••• 25 6 Two sucrose levels on defoliated and undefoliated
plants ••••••••••••••••••••••••• ••••27 7 Four sucrose levels on defoliated plants ••••••••••••••••••28 8 Effect of sucrose at two defoliation levels •••••••••••••••30 9 Effect of sucrose on laxly defoliated plants ••••••••••••••31 1 0 Four defoliation levels on sucrose-treated plants •••••••••32 11 Combinations of growth substances - prelimiDary
experiment •••••• • •• • ••• • • • •. • • · ••• · •• 35 1 2 Effect o f benzyl adenine without sucrose •••••••••••••• · ••••• 36 1 3 Four benzyladenine concentrations with sucrose ••••••••••••37
� Effect of four gibberellic acid concentrations ••••• •••••••�39 15 Effect of four indole aoetic acid concentrations •••• � ••••• � 3 '?
1 6 Combinations of benzyladenine and other growth
substanoes ••••••••••••••••• ••••••••40 1 7 Four hour root elongation at constant temperature ••••••••• 43 18 Response to placing planta in dark and returning
to light ••••••••••••.••• ••••• • ••• • •• 44 1 9 Fall in root elongalion on defoliating or plao1ng
1n dark ••••••••••••••••••••••••••••45 20 Effect of sucrose on plants in dark •• •••••••••• •••••••••••47 21 Defoliation on plants supplied sucrose in dark ••••••••••••48
22 Low intensity l ight on plants supplied sucrose ••••••••••••49 23 Comparison of high light, low light and dark •••••••••· ••••49 24 Fall in root elongationJ effect of low intensit7
light ··· · · · ···50 25 Effect of defoliation on cell length pattern of root
oortu •••••••••••• ·., ••••••••••••• · •• 62 26 Effeot of defoliation and dark on cell length in
mature cortex tissue ••••••••••• ••••64
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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 ••••••••• 1 1 3 Effect of shading on root morphology ••• ••••••••••• ••••••••1 4 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
