Meristems, Growth, and Development in Woody Plants: An Analytical Review of Anatomical

225 Pages·2011·10.63 MB·English

by  Romberger J.

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MICROCOPY RESOLUTION TEST CHART MICROCOPY RESOLUllON TEST CHART

NATIONAL BUREAU OF STAND~RD)-1963-A NATlOO,L BUREAU or ST ANOARDS-1963-A
MERISTEMS, GROWTH,

AND DEVELOPMENT

IN WOODY PLANTS

An Analytical Review of Anatomical,

Physiological, and Morphogenic Aspects

By J. A. Romberger
U.S. Department of A~riculture, Forest Servicfi
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(The author Is Plant Physiologist at the Forest Physiology
Laboratory, Plant Industry Station, Beltsville, Md.)
Technical Bulletin No. 1293 October 1963
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PREFACE
Apical meristems are small. Lateral meristems are. thin. Together
they constitute a physically insignificant fraction of the total mass
of a tree or shrub. Yet the whole fulure of the plant depends upon
the activity of jts meristems. Growth and morphogenesis! and the
control of these processes, are largely localized in the meristems
proper and in their uncillary regions of occasional cell division, con­
tinuing cell enlargement, and cell differentiation. TI~e subject area
encompassing meristems, growth, and development is basic to a wide
range ·of research problems in forestry and horticulture.
This bulletin is intended for students and research workers,in
plant physiology, horticulture, and the forest sciences, who are inter­
ested in the control of growth and development in woody plants.
It. is not a textbook. lllustrations duplicating those readily avail­
able in texts have not been provided. Readers are assumed to have
knowledge of the basic principles of the anatomy, physiology, and
biochemistry of plants, and to have access to textbooks on these sub­
jects.. I have attempted to go beyond the textbook level in analyzing
complex problems, in searching for interrelations between the various
islands of research information, and in providing a guide to the
early as well as the more contemporary literature.
The approach is nonauthoritarian. :Many questions are asked.
Few are answered. Readers are encouraged to speculate and to
doubt and question my interpretations as they see fit. I wish t.o be
regarded not as an expert, or a teacller, but as a fellow student.
Although growth control in woody plants has many special aspects,
it cannot be considered as a subject completely separate from that
of growth control in herbaceous species. :Uuch, or most, of the ex­
perimental work on growth regulators, photoperiodism, and photo­
morphogenesis was done "ith herbaceous species. Some of the evi­
dence discllssed and literature cited in this review is not directly
concerned with trees or shrubs, but such citation and discussion is
nonetheless prerequisite to intel1ige.nt consideration of the specific
problems of growth control in woody plants.
Throughout the reyiew, emphasis is put upon lines of work spe­
cifically aimed at increasing our basic knowledge of meristems and
the control of their act],·jties. The voluminous literature concerning
purely empirical experimentation aimed at eady application in the
field is not stressed.
As a knowledge of political !md social history is indispensable to
social scientists. a knOlylec1f!e of the history of biology is likewise
indispensable to the biological theoretician and experimenter. ~Vith­
ont the past, without an appreciation of past successes and failures,
and their significance to liS. Oll1' fllture aclYallCe would be wavering
ill direction and lacking in momentum. Such considerations. and
the belief that discussions of sincere attempts to arrive at truth are
III
IV PREFACE
never obsolete, prompted use of the historical method of exposition
in most sections of this review.
Plant names are generally the Latin names given in the works
cited. Many original sources give no authorities for the names em­
ployed. None are given here. Some of the names used herein are
not current or are in dispute. Readers who need current names and
authorities must seek information in the papers cited, and elsewhere.
No review of this type can cover all related areas in addition to
the central subject. The very important and closely related subjects
of the control of flowering in woody plants, and the physiology of
seed dormancy and the germination process, are treated only mci­
dentally. A]so outside the area of immediate concern are breaking
of dormancy by deliberate wounding of plants or by applications
of any of a great variety of chemicals having no known relation to
any endogenous l·egulators.
This review is not exhaustive even within the subjects covered.
The goal was to provide access to important lines of work rather
than to cite all significant papers. Some references were intention­
ally omitted because they are included in bibliographies of other
works cited. Some important papers were undoubtedly overlooked,
and numerous recent ones came to my attention too late to be included.
Coverage of some subject areas was modified because of the existence
of relatively recent and readily available reviews -by other authors.
With these limitations understood, I hope that these discussions will
encourage and facilitate further work on the fascinating subject of
meristems and their activity or dormancy in woody plants.
A written discussion is Jinear. Only one aspect of a subject can
be presented at a time. Words, sentences, and paragraphs follow
one another. Each separate fact or idea in turn briefly commands
the reader's attention. But the realm of ideas is not one dimen­
sional. The. numerous fact.s and ideas embodied in this review are
relat.ed to each other more like various points within the volume of
a sphere than like points on a straight line through space. To pro­
mote escape from linearity, numerous cross references have been
pro\-ided in the text. These are indicated in italics within parenthe­
ses, either alone or separated from citations to other works by a
semicolon.
I sincerely appreciate the assistance and advice received .from
many people during the preparation of this bulletin. Particularly
helpful were Edward R. Moser, Librarian, Division of Biology,
California Institute of Technology, and the staff members of the
National Agricultural Library in "Tashington, D.C., and Beltsvi1le,
:Md. D.rs. Bruce :M. Pollock, Harry A. Borthwick, Thomas O.
Perry, and Robert M. Allen made many constructive suggestions
a.fter reading a]] or parts of t.he man uscri pt.
CONTENTS
Pau.
Part 1. Anatomy and physiological morphology______________________ _ 1
Organization of meristems _______________________________________ _
1
Development of the meristem concept___________________________ _ 1
The ol'igin of eells _____________________________ .. ____________ _
1
The apical cell theory_______________________________________ _
3
The histogen theory of apical organization_____________________ _ 4
Transition to modern concepts_______________________________ _
5
Organizll;tion o~ gymnos~rm shoot apices ________________________ _ 6
CytohlstologlCal zonatIOn ____________________________________ _
6
Zone apicale, anneau initial, and meristcm ruedullaire ____________ 12
Urganization of angiosperm shoot apices__________________________ 13
Tuniea-corpus theory_________.-_____________________________ 13
Cytohistological zonation____________________________________ _
16
Meristcm d'attente, anneal! initial, and meristem medullaire______ 18
l\letrarneristem______________________________________________
20
Synopsis on shoot apices_____________________________________ _
20
Organization of root apices__________ ._________________________ _ 21
Root apex versus shoot apex_________________________________ _ 21
Apical cells and histogens____________________________________ _
22
Kiirper-Kappe theory _______________________________________ _
23
Many-celled promeristems versus central cells _____________ .. ____ _ 24
The quiescent center________________________________________ _
2i
Physiological morphology of shoot meristems and buds______________ _ 30
Reactivity of shoot meristems__________________________________ _
30
J\·letabolic differentiation within the meristem___________________ 30
Cultnre of isolated apices ____________________________________ _ 31
Morphogenic regions of the apex_____________________________ _ 32
Special significance of the subapical region_____________________ _ 34.
Origin of leaves, cataphylls, and vascular tissue __________________ _ 35
Initiation of primordia_______________________________________
35
Procambium__________ • ____________________________________
38
Development of leaves ______________________________________ _
41
Development of cataphylls________________• __________________ _ 44
Vegetative buds and the morphogenic cycle ______________________ _ 46
The bud concept____________________________________________
46
A peculiar anatomical feature-the crown ______________________ 4i
Terminal buds_____________________________________________ _
49
A..'(illary buds ______________________________________________ _
54
Adventitious buds__________________________________________ _
58
Physiological processes in buds__________________________________ 59
Shoot tip abortion ___ • ________________________________________ _
62
Inability to form terminal budL _____________________________ _ 62
Physiology of apical abortion ______________ . __________________ _ 63
Physiological anatomy and development in the cambium____________ _ 65
De,-clopmenbl anatomy_______________________________________ _
65
Morphogenic cycles in the vascular cambium________________ .____ _ 68
Part II. Episodic growth and dormancy of shoots____________________ _ il
Concepts, nomenclature, and definitions___________________________ _ il
The dormancy concept and its development._____________________ _ il
Kinds of dormancy-definitions________________________________ _ i3
Alternate growth and dormancy___________________________________ i6
Implications of episodic growth__________________________________ i6
Associated anatomical and cytological changes_________ --_________ _ i8
Analysis of the control problem_________________________________ _ 80
Internal physiological factors___________________________________ _ 80
Why summer growth inhibition?_____________________________ _ 80
Possible root influences ______________________________________ _ 81
Correlated inhibition and apical dominance ____________________ _ 81
v
VI CONTENTS
Part II. Episodic growth and dormancy of shoots-Continued
Analysis of the control problem-Continued Pap
Experimental control of growth and dormancy in various species______ 84
PAinn. Uin8 traoydlluJcet8iotmn t-o-- -p--h_o_to_p_e_r_i_o_d_i_sm__ _in_ _w_o__o_d_y_ p_l_a_n_t_s____ _.. _.. __________________ __ 84
86
89
C~~a~tailp!ay :s~~~~=~========================~============== 92
bign.onioides_______ ___________________________________ _
Weillela flqrida _____________________________________________ _ 93
RChoUrn8u aC yflpqhriindaa _ ____________________________________________________________________________________________ __ 94
95
Acer paeudoplatan.U8____ _____________________________________ _ 96
96
The significance of photoperiodism---------------~---------------- 97
Are photoperiodic receptor and response mechanisms general?_____ 97
Mechanistic implications of photoperiodic responses _____________ _ 99
Possible mechanisms of growth and dormancy controL______________ _ 100
Photomorphogenesis__________________________________________ _
100
Early work on light intensity and spectral quality______________ _ ItO
Duration of light___________________________________________ _
102
Etiolation_________________________________________________ _
104
Phytochrome-a photomorphogenic receptor___________________ _ 106
Responses to light of limited spectral regions____________________ 111
A second photomorphogenic receptor?_________________________ _ 115
Some kinetic aspects of photomorphogenesis and photoperiodism---- 117
Circadian rhythms in relation to photo-and thermoperiodism-------- 119
Endogenous circadian rhythms_______________________________ _
119
Circadian rhythms and photoperiodism------------------------­ 121
Circadian rhythms and thermoperiodism----------------------- 124
Endogenous growth regulators____________________________ ._____ _
Introduction_______________________________________________ _ 125
125
The auxin concept__________________.. _______________________ _
126
Auxins in buds and shoots___________________________________ _
128
Auxins in de\!eloping long shoota versus short shoots_____________ 130
Auxins and cambial activity__________________________. _______ _
133
TGhibeb seirgenlliifnicsa_n_c_e_ _o_f _a_u_x_i_n_s _i_n_ d_o__rm__a_n_c_y_ _c_o_n_t_r_o_L__-_-_-_-_-_-_--_-_-_-_-_-_-_-_- -_ 138
140
Kinins_______________ .. _____________________________________
146
Other possible regulators____________________________________ _
148
Endogenous growth inhibitors_________________________________
150
Interactions_______________________________________________ _
154
N~nP.E:~odic te~perature effects________________________________ _ 157
Chilling reqw.remenw _______________________________________ _
157
Unsatlsfied chillingrequiremellts and dwarfing_________________ _ 161
High temperature and rest induction__________________________ _ 163
W8l1Jl baths as rest breaking agents ___________________________ 164
Part III. Episodic growth and dormancy of roots_____________________ _ 166
Growth and dormancy in roots___________________________________ _
166
Definition of the problem______________________________________ _
166
Seasonal and episodic root growth______________________________ _ 166
Anatomical and physiological aspects____________________________ 171
Control of root growth________________________ _______________ _
~ 175
In retrospect______________________________________________________
177
Literature cited______ • ___________________________________________ _
180
PART I. ANATOMY AND PHYSIOLOGICAL

MORPHOLOGY

ORGANIZATION OF MERISTEMS
Development of the Mel'lstem Concept
~rhe Origin of Cells
The concept of meristems is a relatively recent one. Its formula­
tion depended upon prior evolution of ideas concerning the cellular
structure of organisms and the origin of cens. The evolution of
tllOseideas wa~ slow. Truths which seem obvious to us now were
arrived at by the efforts of generations of dedicated men.
There were undoubtedly many brilliant minds among the bota­
nists and microscopists of the 17th and 18th centuries. They did
an
they could do with the instruments aYailable to them. But the
results of their efforts advanced knowledge of cells and tissues only
a EttIe beyond the levels attained by Grew, Malpighi, and Leeuwen­
hoek. It was h.'lown that cork and wood are cellular jn structure,
but the cell was not recognizee} as the basic structural unit of all
plant parts. Nothing was kno'wll about the odgin of either cellular
structure or of cells.
The great barrier to progress was chromatic aberration in lenses.
Objects under the microscope shimmered with aU colors of the rain­
bow. Details were blurred out and misinterpretation was easy. The
development of achromatic lens systems was a breakthrough of
great significance to biology. Achromatic microscopes became gen­
erally available to biological research institutions in about 1830. A
resurgence of interest in plant anatomy and development began im­
mediately and a great wave of progress followed shortly thereafter.
In 1830 the fact that wood is composed of mostly empty cells was
generally accepted, altl10ugh some question remained about the cel­
lular orIgin of vessels, That other plant parts also consist of cells
was, however still not widely recognized. Modification of the cell
1
concept to include not only the empty, thick-walled chambers of
wood and cork, but. also thin-waned structural units filled with liq­
tI ids and gels came quickly after achromatic microscopes were jn use.
On the basis of detailed studies of the structure of mosses and
other plants Uirbel (1837) maintained that the cen is the funda­
1
mental unit of structure in the plant kingdom. Tre\Tiranus (1835),
J[jrbel (1837), and MoI11 (1845a, b) removed objections to the cel­
lular stl'ucture. of wood n~ssels by obRerving that vessels arise from
files of cel1s 'which lose their end walls.
Xllmel'; and dates In parentheses refer to Literature Citl'd. p. 180.
1
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