New Root Formation in Plants and Cuttings

277 Pages·1986·6.015 MB·English

by  R. L. Peterson, Carol A. Peterson (auth.), Michael B. Jackson (eds.)

NEW ROOT FORMATION IN PLANTS AND CUTTINGS
Developments in Plant and Soil Sciences
Volume 20
1. J. Monteith and C. Webb. eds .•
Soil Water and Nitrogen in Mediterranean-type Environments. 1981. ISBN 90-247-2406-6
2. J.C. Brogan. ed .•
Nitrogen Losses and Surface Run-off from Landspreading of Manures. 1981. ISBN 90-247-2471-6
3. J.D. Bewley. ed .•
Nitrogen and Carbon Metabolism. 1981. ISBN 90-247-2472-4
4. R. Brouwer. I. Galparlkova. J. Kolek and B.C. Loughman. eds .•
Structure and Function of Plant Roots. 1981. ISBN 90-247-2510-0
5. Y.R. Dommergues and H.G. Diem. eds .•
Microbiology of Tropical Soils and Plant Productivity. 1982. ISBN 90-247-2624-7
6. G.P. Robertson. R. Herrera and T. Rosswall. eds ••
Nitrogen Cycling in Ecosystems of Latin America and the Caribbean. 1982. ISBN 90-247-2719-7
7. D. Atkinson et al .• eds .•
Tree Root Systems and their Mycorrhizas. 1983. ISBN 90-247-2821-5
8. M.R. Saric and B.C. Loughman. eds .•
Genetic Aspects of Plant Nutrition. 1983. ISBN 90-247-2822-3
9. J.R. Freney and J.R. Simpson. eds .•
Gaseous Loss of Nitrogen from Plant-Soil Systems. 1983. ISBN 90-247-2820-7
10. United Nations Economic Commission for Europe.
Efficient Use of Fertilizers in Agriculture. 1983. ISBN 90-247-2866-5
11. J. Tinsley and J.F. Darbyshire. eds .•
Biological Processes and Soil Fertility. 1984. ISBN 90-247-2902-5
12. A.D.L. Akkermans. D. Baker. K. Huss-DaneU and J.D. Tjepkema. eds .•
Frankia Symbioses. 1984. ISBN 90-247-2967-X
13. W.S. Silver and E.C. SchrOder. eds .•
Practical Application of Azolla for Rice Production. 1984. ISBN 90-247-3068-6
14. P.G.L. Vlek. ed .•
Micronutrients in Tropical Food Crop Production. 1985. ISBN 90-247-3085-6
15. T.P. Hignett. ed .•
Fertilizer Manual. 1985. ISBN 90-247-3122-4
16. D. Vaughan and R.E. Malcolm. eds .•
Soil Organic Matter and Biological Activity. 1985. ISBN 90-247-3154-2
17. D. Pasternak and A. San Pietro. eds .•
Biosalinity in Action: Bioproduction with Saline Water. 1985. ISBN 90-247-3159-3.
18. M. Lalonde. C. Camire and J.O. Dawson. eds .•
Frankia and Actinorhiza1 Plants. 1985. ISBN 90-247-3214-X
19. H. Lambers. J.J. Neeteson and I. Stulen. eds .•
Fundamental. Ecological and Agricultural Aspects of Nitrogen Metabolism in Higher Plants. 1986.
ISBN 90-247-3258-1
20. M.B. Jackson. ed.
New Root Formation in Plants and Cuttings. 1986. ISBN 90-247-3260-3
21. F.A. Skinner and P. Uomala. eds .•
Nitrogen Fixation with Non-Legumes. 1986. ISBN 90-247-3283-2
22. A. Alexander. ed.
Foliar Fertilization. 1986. ISBN 90-247-3288-3.
23. H.G.v.d. Meer. J.C. Ryden and G.C. Ennik. eds .•
Nitrogen Fluxes in Intensive Grassland Systems. 1986. ISBN 9O-247-3309-x.
24. U.M. Mokwunye and P.L.G. Vlek. eds .•
Management of Nitrogen and Phosporus Fertilizers in Sub-Saharan Africa. 1986.
ISBN 9O-247-3312-x
New Root Formation in Plants
and Cuttings
Edited by
MICHAEL B. JACKSON
Long Ashton Research Station
University of Bristol
UK
1986 MARTINUS NIJHOFF PUBLISHERS ~.
a member of the KLUWER ACADEMIC PUBLISHERS GROUP"
DORDRECHT / BOSTON / LANCASTER
Distributors
for the United States and Canada: Kluwer Academic Publishers, 190 Old Derby
Street, Hingham, MA 02043, USA
for the UK and Ireland: Kluwer Academic Publishers, MTP Press Limited,
Falcon House, Queen Square, Lancaster LAI lRN, UK
for all other countries: Kluwer Academic Publishers Group, Distribution Center,
P.O. Box 322, 3300 AH Dordrecht, The Netherlands
Library of Congress Cataloging in Publication Data
Main entry under title:
New root formation in plants and cuttings.
(Developments in plant and soil sciences ; 20)
Includes indexes.
Bibliography: p.
1. Roots (Botany) 2. Plant cuttings. 3. Plant
regulators. I. Jackson, Michael B. II. Title:
Root formation in plants and cuttings. III. Series:
Developments in plant and soil sciences v. 20.
QK644.N48 1986 581.3 85-25902
ISBN-13: 978-94-010-8438-3 e-ISBN -13: 978-94-009-4358-2
DOT: 10 .1 007/978-94-009-4358-2
Copyright
© 1986 by Martinus Nijhoff Publishers, Dordrecht.
Softcover reprint of the hardcover lst edition 1986
All rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means, mechanical,
photocopying, recording, or otherwise, without the prior written permission of
the publishers,
Martinus Nijhoff Publishers, P.O. Box 163, 3300 AD Dordrecht,
The Netherlands.
In memory of The AFRC Letcombe Laboratory
(Deceased, 31st March, 1985)
VII
Introduction
The formation of roots is in some respects one of the least fundamentally
understood of all plant functions. Propagation by cuttings is the aspect that will
occur first to most gardeners and horticulturists, and it is certainly the most useful
application. But any observant traveller in the tropics can notice that some trees
have the habit of forming roots in the air. Climbers like Cissus bear long fine
strings of roots hanging down. Pandanus trees tend to have stout aerial roots
issuing from the bases of the long branches, while the tangle of roots around the
trunk of many of the Ficus species is characteristic. In Ficus bengalensis, in
particular, stout cylindrical roots firmly embedded in the ground from a height of
3 to 5 meters give support to the long horizontal branches, enabling them to
spread still further. In the big old specimen at Adyar near Madras, the spread of
these branches all around the tree, each with a strong root growing out every few
meters, makes a shaded area under which meetings of almost 5000 people are
sometimes held.
The history of how the formation of roots on stem cuttings was found to be
under hormonal control is worth repeating here. It was the demonstration by van
der Lek in Holland in 1924 that grape cuttings tended to form roots directly below
a young bud or shoot, and on the same side of the stem, that led to the modern
study of the physiology of root formation. Frits Went, who had always been
impressed by Julius Sachs' idea of a root-forming substance, went to work on the
subject in 1929 when he left Utrecht to work for a while in Java. Together with
Raymond Bouillenne; he found that 'Dedek', the extract of rice polishings that
had been prepared for Jansen and Donath's famous isolation of thiamine, pro
moted the rooting of Acalypha stem cuttings. Although the active factor in this
complex extract was not identified, the simple fact that there must be a root
forming or root-promoting substance in the extract did give reality to the Sachsian
idea. Thus when Went came to the California Institute of Technology in 1933,
where I had been working on the extraction and identification of auxin from
cultures of Rhizopus, it was natural that we should join forces to look for a root
forming substance, or 'rhizocaline', which evidently had a real existence. The
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auxin bioassay was, of course, for coleoptile elongation. It quickly became
apparent, however, that the highly concentrated and partially purified prep
arations of auxin had powerful rhizocaline action, and Went's ingenious and
highly repeatable bioassay with the stems of etiolated pea seedlings showed that,
surprisingly, the root-forming ability went parallel with the auxin action as
purification proceeded. To the last it seemed improbable that auxin, then viewed
as perhaps identical with Sachs' stem-forming substance, could be identical with
the proposed root-forming substance, but the crystallization of indole-acetic acid,
and the testing of analogues, clinched the matter. The induction of splendid root
systems on commercial cuttings - first on citrus by Bill Cooper - left no doubt of
the potential horticultural utility of the discovery. The story is a good example of
the highly practical and down-to-earth results that come from pure basic re
search, driven only by curiosity.
It was almost a quarter of a century later when Skoog and Miller discovered the
cytokinins and showed that they acted as 'shoot-forming substances', at least in
tissue cultures. As is well known, the cytokinins antagonize the inhibiting effect
of auxin on the development of lateral buds, and it is now beginning to seem
probable that this so-called 'apical dominance' exerted by auxin is actually a
balance between the polarly downward moving auxin that inhibits bud growth,
and an upward stream of cytokinin coming mainly from the roots that promotes
bud growth. What is less well known is that there is a corresponding balance in the
formation of lateral roots on a main root. Although auxin does inhibit root
elongation it promotes the formation of lateral roots (in line with its root-forming
action on stems) and here the cytokinins clearly act as inhibitors. Thus the
hormonal balance in roots is a sort of mirror image of that in shoots, with the roles
of auxin and cytokinin as inhibitor and promoter simply reversed. In this way the
organization and control of the plant's behaviour has remarkable symmetry.
However, comprehension of the biochemistry that underlies this symmetry will
be for the future. Some aspects ofthe hormonal balance within the root are taken
up in detail later in this book. Indeed, the book may represent the first occasion
when lateral root formation on roots is presented in the context of the more
extensively studied formation on roots on stem tissue.
As was said at the outset, certain mysteries remain. The basic difference
between plants that are easy to root and those that are difficult or refractive is still
elusive. So is the evident relationship between ease of rooting and juvenility of
form. So also, unfortunately, is the practical problem of inducing the difficult
plants to change their behaviour. In some cases there is apparently an inverse
relation between ease of rooting and rate of elongation. But then all the more
strange is the behaviour of such plants as the humble blackberry, which manages
to combine rapid elongation of internodes with profuse root formation at nodes.
It is ~aid that some six million acres of Chile is occupied by blackberries that,
following innocent introduction by some settler, have entrenched themselves in
this way. Thus although the present book is most valuable in presenting the
IX
quantity of knowledge and experience that has been accumulated about the
theory and practice of root formation, it also makes evident that generalizations
about the behaviour of 'plants' have still to be made with caution.
I am honoured to have the opportunity to introduce a book by such an array of
expert and knowledgeable authors, and I am certain that it will prove of great and
immediate value to both pure and applied researchers.
Santa Cruz KENNETH V. THIMANN
California
XI
Preface
The study of plant roots is currently enjoying something of a resurgence. Perhaps
we are coming to realize more keenly than before the benefits to agriculture and
horticulture that can flow from such work. Furthermore, the essential nature of
root research for any understanding of plants as whole organisms that interact in
complex ways with their environment is self evident. The key position of root
systems in the broader biological context is abundantly clear from a realization
that their evolution was a pre-requisite for the extensive colonization by plants of
'dry-land' some four hundred million years ago. The workings of roots are thus
central to the existance and survival of plants on the land and indeed indirectly to
the survival of almost all terrestrial creatures. Thus, one cannot at all easily
overestimate the importance of plant root systems and the need to understand
them.
The attributes of roots that assured the success of plants as terrestrial colonizers
are equally vital to the success of today's crops and forests. Their cultivation is
largely a matter of tending the root environment and thus of manipulating roots
and root-based processes. Recognition of this has led to the publication in recent
years of several books about roots. They concentrate principally upon root
system morphology, root growth and more especially on root functioning and its
interaction with environment (see the book list on page XIII). There is also
evidence that some authors, concerned with more natural environments and with
conservation matters, are also aware of the importance of plant roots for the
survival or successful management of vegetation in uncultivated areas. Sur
prisingly, very little is written in these publications about the formation of roots,
the underlying physiological processes that guide this formation nor of how this
knowledge can be of practical help, particularly in horticulture. One aim of the
present book is to begin to rectify this shortcoming.
In seven chapters, the formation of new roots on the existing framework of
older roots (lateral rooting), and the formation of adventitious roots from other
plant organs are considered. Lateral rooting and the branched structures it forms
are essential if plants are to extract water and inorganic nutrients efficiently from
XII
the soil. Lateral roots are also thought to be a source of hormones needed by the
shoot system. On the other hand, adventitious rooting lies at the heart of a huge
industry concerned with the vegetative propagation of desirable plant material,
mostly from cuttings. But adventitious roots have another dimension, as highly
diverse but functional organs of intact plants. This much neglected subject is also
considered in this volume.
The book is not addressed exclusively to anyone group. I hope that in the
reading, research workers, lecturers and students in the basic or applied plant
sciences, agriculturists, horticulturists, plant propagators and indeed anyone
whose· professional life or natural curiosity draws them to an interest in plant
roots will learn much that is useful and worthwhile.
Long Ashton, August 1985 MICHAEL B. JACKSON