Table Of ContentPHOTOSYNTHESIS,
PHOTORESPIRATION, AND
PLANT PRODUCTIVITY
ISRAEL ZELITCH
Department of Biochemistry
The Connecticut Agricultural Experiment Station
New Haven, Connecticut
Academic Press 1971
New York and London
COPYRIGHT © 1971, BY ACADEMIC PRESS, INC.
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Preface
In this book I have attempted to provide advanced undergraduates, graduate
students, teachers, and research workers in a number of disciplines with a
perspective of photosynthesis and how it may be increased. Thus many
processes other than photosynthesis that affect the productivity of plants
have been examined from the standpoint of enzyme chemistry, chloroplasts,
leaf cells, and single leaves. Finally, the function of all of these in a stand
of plants growing outdoors and subject to the overriding influence of
climate has been considered. I have had to deal with elements of physics,
biochemistry, plant physiology, genetics, climatology, agronomy, and other
sciences to varying degrees. Wherever possible I have tried to evaluate our
more recent knowledge, to point out areas of uncertainty, and to indicate
promising approaches for future investigation. Examples were taken from
higher plants when they were available, although studies with algae and
photosynthetic bacteria have also been examined.
Most of this book deals with the advances of the sixties, but sufficient
historical background is provided so that the foundations on which this
ix
χ Preface
knowledge was based may be fully appreciated. The past decade may be
remembered for the Green Revolution in which agricultural scientists
demonstrated that with an input of suitable genetic material and increased
nutrient supply the yield of certain crops which had only doubled in the
previous one hundred years was at least doubled again. But scientists
believe that the next large increases in productivity must come from the
application of the newer findings about photosynthetic carbon assimila-
tion. Fortunately, research during the last decade has created impressive
advances in our understanding of these processes.
Some of the newer and often unexpected knowledge revealed during the
sixties that I have considered includes the realization that rates of enzymatic
reactions are often controlled by small regulator molecules; findings about
the detailed structure and function of chloroplasts and other organelles
and their variability; substantial evidence that photosynthesis requires at
least two separate photoacts; the unraveling of many details about the
mechanism of photosynthetic electron transport and photophosphoryla-
tion; the appreciation of the importance of diffusive resistances to carbon
dioxide assimilation, especially the role of stomata; the grasping of the
importance of dark respiration in diminishing productivity; the discovery
that the great differences in net photosynthesis that occur between many
species and varieties is largely caused by a newly recognized type of respira-
tion—photorespiration turned on by light; and the coping with the com-
plexities of illumination and climate within the real canopies made by the
leaves of crops that feed us.
Readers may wonder how a biochemist became interested in these
diverse subjects and even learned the language used by investigators in
other disciplines. For this I must thank my colleagues at The Connecticut
Agricultural Experiment Station with whom I have had the opportunity
to discuss these important problems for many years. Thus by sometimes
asking what might have appeared to be "foolish" questions, in due course
I began to converse about these subjects relatively painlessly.
By sharing the fruits of these conversations with readers, it is my fondest
hope that we may be able to work together more easily in order to alleviate
the widespread suffering that will otherwise result from an inadequate
world food supply.
ISRAEL ZELITCH
Acknowledgments
The orderly completion of this book involved the cooperation of a number
of people. I wish to thank Dr. Graham Berlyn, Dr. Vernon E. Gracen, Jr.,
Mr. Fritz Goro, and Dr. Eldon H. Newcomb for providing illustrations,
some of them before publication. Material in advance of publication was
also received from Dr. William A. Jackson, Dr. Jack Preiss, and Dr. Peter
Trip. Dr. Paul E. Waggoner kindly supplied unpublished data that was
used extensively in Chapter 9. Miss M. Gregory, Jodrell Laboratory,
Royal Botanic Garden, Kew, England, provided an analysis of earlier
investigations about chloroplasts in the bundle-sheath cited in a footnote
in Chapter 2.
Friendly critics in several departments of The Connecticut Agricultural
Experiment Station (and nearby) offered suggestions about various chapters:
Dr. Peter R. Day, Dr. Kenneth R. Hanson, Dr. Evelyn A. Havir, Dr.
Jean-Yves Parlange (Engineering and Applied Science, Yale University),
Dr. Raymond P. Poincelot, Jr., Dr. Ernest G. Uribe (Biology Department,
Yale University), and Dr. Paul E. Waggoner. Two colleagues read the entire
xi
xii Acknowledgments
manuscript at one or more stages, and thus I am especially grateful for the
counsel of Dr. Η. B. Vickery (Biochemist Emeritus) and Dr. Gary Heichel
(Department of Ecology and Climatology).
I have been greatly helped in many ways by Mrs. Ruth DiLeone, who
drafted most of the figures and also typed the manuscript, and by Mr.
John A. Marcucci, who assisted with library searches.
Conversion Units
LIGHT AND ENERGY
Illumination of 1 foot candle (ft-c) = 10.764 lumens m"2 (lux)
Total maximum incident sunlight = 10,000 ft-c = 108,000 lux
1 watt = 107 erg sec-1
1 cal = 4.186 χ 107ergs
Maximum incident solar irradiation at earth's surface = 1.2 cal cm"2 min"1
1 watt m"2 = 103 erg sec"1 cm"2 = 1.43 χ 10"3 cal cm"2 min"1 (400 to
700 nm)
Maximum visible solar irradiation (400 to 700 nm) = 0.6 cal cm -2 min"1 =
42 χ 104 erg sec"1 cm"2 = about 9 iieinsteins cm"2 min"1 absorbed
by an average leaf
OTHER CONVERSIONS
1 nm = 10"9 m = 1 ιημ = 10 Angstrom (A)
ppm of C0 = μΐ per liter by volume
2
xiii
xiv Conversion Units
300 ppm of C0 = about 9 χ 10 ~6 Μ free C0 in solution in pure water
2 2
1 acre = 2.47 hectare (ha) or 2.47 χ 104 m2
1 pound per acre = 1.12 kg ha-1
Wind speed of 100 cm sec"1 = 2 miles per hour
AVERAGE LEAF COMPOSITION
1 dm2 projected area = 2.0 gm fresh weight of lamina = 3.0 mg chloro-
phyll = 6 mg protein Ν = 40 mg protein
1 Morphology of Leaf Cells
An aim of this monograph is to provide a basis for understanding the
main factors concerned with regulating plant productivity in communities
of plants. However, before one can evaluate how plants function in a stand,
it is first necessary to examine the biochemical, physiological, and physical
activities of single leaves. Hence it becomes necessary to study the nature
of the kinds of cells in leaf tissues as well as the organelles they contain,
and to examine especially the biochemical and physiological functions
associated with these various parts.
Leaf cells possess the fundamental capabilities and carry out the processes
common to all other living cells, but perhaps of greater importance in this
discussion are the unique properties not encountered elsewhere. Some of
these special attributes include the unusual cell wall structure surrounding
the cell protoplasm; the effects of specific growth regulators; and the
anatomic features specially adapted to the control of the uptake of inorganic
salts and water and the movement of oxygen and carbon dioxide to and
from the atmosphere. Higher plants are autotrophic organisms, obtaining
3
4 /. Biochemical and Photochemical Aspects
most of their carbon compounds from atmospheric carbon dioxide; hence
the photosynthetic apparatus is of special interest. The photosynthetic cells
of higher plants are fairly autonomous and carry out large numbers of
biochemical reactions, some of which result in the biosynthesis of unique
natural products. Many such substances have still not been identified and
many other compounds are known to be present for which nb metabolic
role has yet been perceived. In this discussion, I shall consider only those
biochemical and physiological aspects of higher plant metabolism that are
believed to be closely related to productivity.
A. THE CUTICLE AND SURFACE WAXES
Certain anatomic features of leaves must first be considered. Examina-
tion of the cross section of typical leaf blades (Figs. 1.1, 1.2, 1.3) shows
that a waxy layer covers the surface of the cuticle. These waxes, so-called
because of their physical rather than their chemical characteristics, were
studied intensively by A. C. Chibnall and his colleagues during the period
between 1930 and 1950. They were able to isolate and identify many of the
substances present by laborious fractional crystallization followed by X-
ray analysis. Present-day techniques of separation and identification, espe-
cially thin-layer chromatography and gas chromatography, coupled with
mass spectrometry, have made the task of identifying the compounds of
leaf waxes much easier and more certain.
FIG. 1.1. Cross section of a maize leaf showing chloroplasts in the bundle-sheath as well as in
the mesophyll (provided by G. Berlyn).
