Germination Control. Metabolism, and Pathology

450 Pages·1972·6.722 MB·English

by  T.T. Kozlowski (Eds.)

PHYSIOLOGICAL ECOLOGY
A Series of Monographs, Texts, and Treatises
EDITED BY
T. T. KOZLOWSKI
University of Wisconsin
Madison, Wisconsin
T. T. KOZLOWSKI. Growth and Development of Trees, Volumes I and II -
1971
DANIEL HILLEL. Soil and Water: Physical Principles and Processes, 1971
J. LEVITT. Responses of Plants to Environmental Stresses, 1972
V. B. YOUNGNER AND C. M. MCKELL (Eds.). The Biology and Utilization
of Grasses, 1972
T. T. KOZLOWSKI (Ed.). Seed Biology, Volumes I and II - 1972; Volume
III — in preparation
YOAV WAISEL. The Biology of Halophytes, 1972
SEED BIOLOGY
Edited by
T. T. KOZLOWSKI
DEPARTMENT OF FORESTRY
UNIVERSITY OF WISCONSIN
MADISON, WISCONSIN
VOLUME II
Germination Control, Metabolism, and Pathology
ACADEMIC PRESS New York and London 1972
COPYRIGHT © 1972, BY ACADEMIC PRESS, INC.
ALL RIGHTS RESERVED
NO PART OF THIS BOOK MAY BE REPRODUCED IN ANY FORM,
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United Kingdom Edition published by
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LIBRARY OF CONGRESS CATALOG CARD NUMBER: 71-182641
PRINTED IN THE UNITED STATES OF AMERICA
LIST OF CONTRIBUTORS
Numbers in parentheses indicate the pages on which the authors' contributions begin
AREF A. ABDUL-BAKI (283), Seed Quality Investigations, Market
Quality Research Division, Agricultural Research Service, United
States Department of Agriculture, Plant Industry Station, Beltsville,
Maryland
JAMES D. ANDERSON (283), Seed Quality Investigations, Market Quality
Research Division, Agricultural Research Service, United States
Department of Agriculture, Plant Industry Station, Beltsville,
Maryland
KENNETH F. BAKER (317), Department of Plant Pathology, University
of California, Berkeley, California
TE MAY CHING (103), Department of Farm Crops, Oregon State Uni­
versity, Corvallis, Oregon
Dov KOLLER (1), Department of Agricultural Botany, The Hebrew Uni­
versity of Jerusalem, Rehovot, Israel
T. A. VILLIERS (220), Department of Plant Biology, University of Natal,
Durban, South Africa
vii
PREFACE
Man's existence and health are directly or indirectly dependent on
seeds. This fact has for many years pointed out the urgent need for a
comprehensive coverage of information on seed biology. The importance
of this work became even greater during the recent years of rapid popu­
lation increases throughout the world. It was with these thoughts in mind
that this three-volume treatise was planned to bring together a large body
of important new information on seed biology.
The subject matter is wide ranging. The opening chapter outlines man's
dependency on seeds as sources of food and fiber, spices, beverages,
edible and industrial oils, vitamins, and drugs. Harmful effects of seeds
are also mentioned. Separate chapters follow on seed development, dis­
semination, germination (including metabolism, environmental control,
internal control, dormancy, and seed and seedling vigor), protection from
diseases and insects, collection, storage, longevity, deterioration, testing,
and certification. These books were planned to be readable and inter­
disciplinary so as to serve the widest possible audience. They will be
useful to various groups of research biologists and teachers, including
agronomists, plant anatomists, biochemists, ecologists, entomologists,
foresters, horticulturists, plant pathologists, and plant physiologists.
The work has many practical overtones and will also be of value to seed
producers and users.
These volumes are authoritative, well-documented, and international
in scope. They represent the distillate of experience and knowledge of a
group of authors of demonstrated competence from universities and
government laboratories in England, India, Israel, South Africa, and the
United States. I would like to express my deep personal appreciation to
each of the authors for his contribution and patience during the produc­
tion phases. The assistance of Mr. W. J. Davies and Mr. P. E. Marshall
in index preparation is also acknowledged.
T. T. KOZLOWSKI
ix
CONTENTS OF OTHER VOLUMES
Volume I Importance, Development, and Germination
1. Importance and Characteristics of Seeds
T. T. Kozlowski and C. R. Gunn
2. Development of Gymnosperm Seeds
H. Singh and Β. M. John
3. Development of Angiosperm Seeds
S. P. Bhatnagar and Β. M. John
4. Anatomical Mechanisms of Seed Dispersal
Abraham Fahn and Ella Werker
5. Seed Germination and Morphogenious
Graeme P. Berlyn
6. Seed and Seedling Vigor
Bruce M. Pollock and Eric E. Roos
Author Index —Subject Index
Volume III Insects, and Seed Collection, Storage, Testing,
and Certification
1. Seed Insects
G. E. Bohart and T. W. Koerber
2. Seed Collection and Identification
Charles R. Gunn
3. Seed Storage and Longevity
James F. Harrington
4. Insects Attacking Seeds During Storage
R. W. Howe
5. Essentials of Seed Testing
Oren L. Justice
6. Seed Certification
J. Ritchie Cowan
Author Index — Subject Index
xi
1
ENVIRONMENTAL CONTROL
OF SEED GERMINATION
Dov Roller
I. Environmental Control of Germination and Its
Biological Significance 2
A. The Dormant State and Its Biological Implication 2
B. Termination of the Dormant State 3
C. Environmental Control 4
7
D. Dormancy and Survival 6
II. Environmental Indicators and Plant Perception
lz
A. Requirements and Indicators 7
4 1
B. Perception -
5 1
III. Immediate Responses
A. Temperature Regime
2 5
B. Radiation Regime ^5
C. Water Relations
8 6
D. Chemical Environment 59
E. Time
F. Interactions and Conditioning 71
IV. Postmaturation Conditioning 76
A. Effects of Dispersal Mechanisms 80
B. Temperature 82
C. Radiation 84
D. Water Relations 86
E. Biotic Influences 88
F. Fire 90
V. Prematuration Conditioning 91
References 93
1
2 DOV KOLLER
I. Environmental Control of Germination and Its Biological Significance
A. The Dormant State and Its Biological Implication
One of the most universal characteristics of practically all existing
plant species is that at least once, and in many instances several times,
during their life cycle they produce specialized cells, or multicellular
bodies, that exhibit the phenomenon which has become known as dor­
mancy. With few exceptions, these dormant structures are a develop­
mental antithesis of the tissues from which they develop. The latter are at
the peak of differentiation and at their lowest potential for resuming active
growth. On the other hand, the former are at their highest potential for
resuming active growth, to the extent of initiating an entirely new life
cycle, or a new phase of the existing cycle. At the same time, they are
essentially at their most undifferentiated state, although they may be
encapsuled in structures and tissues of the highest degree of complexity
and differentiation.
There is a dramatic quality to this dormancy, since formation of the
dormant structures is commonly associated with a remarkable intensifica­
tion of metabolic, synthetic, and morphogenetic activities, all of which
come to an abrupt and almost simultaneous end. Onset of dormancy
nevertheless appears to be much more than a mere cessation of the afore­
mentioned activities. It apparently involves a sequence of events as
orderly as that which is encountered in the formation of the dormant
structures. It is tempting to visualize the operation of sequential gene
activity as postulated by Heslop-Harrison (1963) for the process of
differentiation of a floral apex. However, our understanding of the mech­
anism which controls the sudden cessation in all these activities is both
fragmentary and elusive, and will be dealt with in other chapters of the
present volume.
The remarkable fact about this onset of dormancy is that it takes place
at a time when the external environment to which the plant is exposed is
in no apparent way unfavorable for continued metabolic, synthetic, or
morphogenetic activities. The imposition of dormancy is therefore most
likely to be controlled endogenously. The ultimate control is probably
located in the tissues of the mother plant. Nevertheless, there is ample
evidence that in many if not most plants the formation of the dormant
structures is initiated under a more or less specific combination of en­
vironmental variables. Thus, even when the morphological development
of these structures and their physiological transition to the dormant state
are under endogenous control, the primary timing mechanism which
initiates these events depends on perception of and response to environ-
1. ENVIRONMENTAL CONTROL OF SEED GERMINATION 3
mental signals, such as photoperiod or cold in the case of many flowering
plants, availability of minerals or light in many algae, etc.
The drastic reduction in physiological activities which is integrated in
the dormant state is commonly associated with development of external
protective tissues and (at least in seed plants) with a drastic reduction
in hydration of the cytoplasm. All these combine to make the dormant
structure much more resistant to unfavorable environments than the
plant which produced them. Dormancy thus becomes associated with
resistance against, or tolerance of adverse environmental conditions.
Dormancy must therefore have evolved primarily as a solution to the
periodic, as well as nonperiodic, changes in the environment, which
makes it difficult if not impossible for the plant to function properly, or
even exist, during certain periods. The life span of most higher plants is
limited by their very nature (monocarpic species), by limitations in their
environmental resources, or by pathogenic agents. The investment in
dormant cells or seeds which possess the highest potential for resuming
growth and forming a fresh individual is in the nature of general insurance
for survival of the species. Dormancy also appears to be a natural evolu­
tionary consequence of most forms of plant dispersal, with the exception
of fragmentation and the like, since the environments through which dis­
persal takes place are almost invariably hostile to active growth. More­
over, the time passed in transit through the hostile environment is rela­
tively indeterminate.
B. Termination of the Dormant State
The state of dormancy is overtly terminated when active metabolism,
synthesis, and finally growth are resumed. In seeds (and spores) the re­
sumption of these activities is identified with the term germination. Such
postgerminative activities can only take place in environments within
which the parent plant could function properly. The requirement for
photosynthetically active radiation and for external mineral supply may
be deferred for a length of time which depends on the size of the organic
and mineral reserves within the seed. This leaves the immediate post­
germinative growth activity with virtually few and simple requirements
from the environments. One of these is an adequate moisture supply, yet
which would not interfere with the gaseous exchange which is essential
for aerobic respiration and adequate supply of metabolic energy. Another
such requirement is for "normal" temperature, i.e., within the range which
is suitable for normal growth of the more mature seedling. Ostensibly,
therefore, exposure of the seeds to environments consisting of adequate
moisture, aeration and "normal" temperature, should suffice also for
germination to take place. However, experience of foresters, horti-
4 DOV KOLLER
culturists, and agronomists through the years has shown that germination
under such conditions can turn out to be negligible or is at best a slow
process and erratic to the point of unpredictability. Rapid, simultaneous
germination in high percentages under such conditions is the exception
rather than the rule. By far most exceptions occur among species which
have been longest under cultivation, such as cereals which originated in
the Old World (e.g., Tang and Chiang, 1955; Takahashi and Oka, 1957),
for the obvious reason that they had been continuously selected for high,
rapid, and simultaneous germination. The phenomenon of erratic, in­
complete, or otherwise unsatisfactory germination presented consider­
able difficulties for agriculture and therefore resulted in the establishment
of "seed testing" or "seed analysis," which was primarily aimed at
certifying seed quality in terms of expectancy of maximal potential field
performance. The vast amounts of experimental data which were gathered
by the efforts of numerous seed analysts showed that in a great number of
species germination can be hastened, its rates increased and its final per­
centages improved by a variety of means. The capacity for germination
was in many instances lowest soon after harvest and afterward improved
with time. As a result, the failure of apparently mature seeds to germin­
ate when provided with the moisture and temperature which are normally
adequate for growth was treated as a manifestation of dormancy, with the
idea that it was most probably a direct continuation of the primary dor­
mancy which the seeds enter in the normal course of their maturation, as
described above. Out of these studies also grew the realization that the
dormancy which is involved in preventing germination from taking place
readily under apparently "normal" conditions may be an evolutionary
safeguard against the uncertainty of the plant's environment. Catastrophies
which may occur will involve only a fraction of the seeds which had been
produced, and since the risk of annihilation is minimized, their effect on
the population of the species as a whole will therefore be temporary.
C. Environmental Control
The proceedings of various national seed testing associations, and of
the International Association (Comptes Rendus, Association Inter­
nationale d'Essais des Semences) provide a wealth of detailed informa­
tion on the different methods which were found most effective in obtaining
the maximal germination response in the different plant species. Some of
the treatments which were successful in inducing germination of such dor­
mant seed were clearly agrotechnical, in the sense that they were entirely
unavailable to the seed without man's technical assistance. Such was the
case, for instance, with seeds which responded to pretreatment in con­
centrated sulfuric acid, or in boiling water, or to mechanical damage to