Table Of ContentLight as an Energy Source
and Information Carrier in
Plant Physiology
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Volume 287 - Light as an Energy Source and Information Carrier in Plant Physiology
edited by Robert C. Jennings, Giuseppe Zucchelli, Francesco Ghetti, and
Giuliano Colombetti
Series A: Life Sciences
Light as an Energy Source
and Information Carrier in
Plant Physiology
Edited by
Robert C. Jennings and
Giuseppe Zucchelli
University of Milan
Milan, Italy
and
Francesco Ghetti and
Giuliano Colombetti
CNR Institute of Biophysics
Pisa, Italy
Plenum Press
New York and London
Published in cooperation with NATO Scientific Affairs Division
Proceedings of a NATO Advanced Study Institute on
Light as Energy Source and Information Carrier in Plant Photophysiology,
held September 26 - October 6, 1994,
in Volterra, Italy
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Library of Congress Cataloging-in-Publication Data
On file
ISBN-13: 978-1-4613-8039-9 e-ISBN-13: 978-1-4613-0409-8
001: 10.1007/978-1-4613-0409-8
© 1996 Plenum Press, New York
Softcover reprint of the hardcover 1 st edition 1996
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PREFACE
A NATO Advanced Study Institute on "Light as Energy Source and Information
Carrier in Plant Photo physiology" was held at Volterra, Italy, from September 26 to October
6, 1994, in order to consider the fundamental role that light plays in plant growth and
development. This book summarises the main lectures given at this meeting which
concentrated on both photochemical energy conversion and signalling (photosensing)
aspects.
Light harvesting and conversion into chemical energy in photosynthesis occurs at the
level of chlorophyll/carotenoid containing photosystems in plants. Pigments are non-
covalently bound to a variety of polypeptides which serve as a specific scaffolding, necessary
to determine the energy coupling between pigments and thus allowing rapid excitation
energy trasfer from the antenna to the special reaction centre chlorophylls. Data from
transient, time resolved spectroscopies, in the femtosecond and picosecond domain, together
with model calculations, suggest that this process occurs in the 20-100 picosecond time
span. The special ~ll u~ture of reaction centre complexes, ensures rapid primary charge
separation, probably in the order of 1-3 picoseconds, with subsequent charge stabilisation
reactions proceeding in the hundreds of picoseconds range. The recently resolved
crystallographic structure of LHCII, the principal antenna complex of plants, allows precise
determination of pigment-pigment distances and thus permits calculation of approximate
chlorophyll-chlorophyll Forster hopping rates, which are in good agreement with time
resolved measurements.
A number of lectures dealt with the complex phenomenon of light induced inhibition of
photosynthetic activity (photoinhibition) and the protective mechanisms plants have evolved
to counteract this. These processes occur mainly at the level of photo system II with reaction
centres of this photo system being particularly sensitive to high iight fluxes. Quenching
mechanisms, which thermally degrade excited states and which appear to be mainly localised
in the external antenna complexes of photo system II, are effective in reducing excited state
levels many-fold, in a fashion which is modulated by the light flux itself. The fact that the
chlorophyll spectral forms are not organised as an energy "funnel" with respect to reaction
centres in photosystem II increases the effectiveness of such control mechanisms.
The effect of ultraviolet radiation on both terrestrial and aquatic ecosystems was also
dealt with. Increases in ultraviolet fluxes, particularly interacting with other environmental
stress factors, can induce significant damage in plants, with photosystem II being particularly
sensitive. The effect of ultraviolet radiation on the vertical distribution phytoplankton in the
water column may be significant.
Photosensing processes are based on a variety of strategies which detect either time-
integrated light quantity, spectral quality, light direction via intracellular light gradients in
which such optical phenomena as absorption, refraction, intereference and dichroism are
involved. Action spectroscopy is the principal technique which permits identification of a
photoreceptor though problems associated with host-induced absorption shifts, absorption
v
screening and scattering can be considerable. Genetic and molecular biological manipulations
can also be an important tool in identifYing photoreceptors as demonstrated by recent studies
on the different morphogenetic roles of the family of phytochrome types via the use of
specific phytochrome mutants. Phytochrome, by far the best characterised
photomorphogenic photoreceptor, has ideal absorption characteristics to sense the dramatic
changes in the terrestrial light environment within and underneath plant canopies. Progress
has been made in recent years in understanding phytochrome phytochemistry.
Phototransformation involves Z{l5)--E{l5) isomerisation which occurs within a few
picoseconds. Subsequent changes in the a-helical folding near the N-terminus may be
important in determing the biochemical and physiological activity of the phototransformed
molecule.
R.C. Jennings
G. Zuc~helli
F. Ghetti
G. Colombetti
Milano, Italy
Pisa, Italy
vi
CONTENTS
Photosynthesis: An Overview ............................................. .
G. Forti
Photosynthetic Electron Transfer and Energy Transduction in Plants . . . . . . . . . . . . . .. 17
D. R. Ort and J. Whitmarsh
Specific Features of Excitation Migration in Photosynthesis ..................... 31
A. Yu. Borisov
Biochemistry and Molecular Biology of Pigment Binding Proteins . . . . . . . . . . . . . . .. 41
R. Bassi, E. Giuffra, R. Croce, P. Dainese, and E. Bergantino
Spectral Heterogeneity and Energy Equilibration in Higher Plant Photosystems ..... 65
R. C. Jennings, G. Zucchelli, L. Finzi, and F. M. Garlaschi
Photosynthetic Reaction Centers ........................................... 75
P. Mathis
Photoinhibition of Photosynthesis .......................................... 89
N. R. Baker
Nonphotochemical Quenching of Chlorophyll Fluorescence ..................... 99
P. Horton
Regulation of Excited States in Photosynthesis of Higher Plants .................. 113
J.-M. Briantais
Chirally Organized Macrodomains in Thylakoid Membranes. Possible Structural and
Regulatory Roles .................. : ................................ 125
G. Garab
Interaction ofUV Radiation with the Photosynthetic Systems .................... 137
J. F. Bornman
Molecular Basis of Photoreception .......................................... 147
F. Lenci, N. Angelini, and A. Sgarbossa
Photomorphogenic Systems ............................................... 159
W. R. Briggs, E. Liscum, P. W. Oeller, and J. M. Palmer
vii
Overview of Photos en sing in Plant Physiology ................................ 169
W. Haupt
Mechanisms of Photoreception: Energy and Signal Transducers .................. 185
D.-P. Hader
Light Signal Transduction Mediated by Phytochromes .......................... 197
D. Sommer and P.-S. Song
Light Penetration into the Canopy of Terrestrial Ecosystems ..................... 219
M. G. Holmes
Light Penetration and Effects on Aquatic Ecosystems ........................... 231
D.-P. Hader
Interception of Light and Light Penetration in Plant Tissues ..................... 243
M. G. Holmes
Photosensory Transduction in Flagellated Algae ............................... 263
R. Marangoni, E. Lorenzini, and G. Colombetti
Action Spectroscopy ..................................................... 275
F. Ghetti and G. Checcucci
Photoregulation of Fungal Gene Expression .................................. 285
E. Cerda-Olmedo and L. M. Corrochano
Phototropism in Phycomyces .............................................. 293
E. Cerda-Olmedo and V. Martin-Rojas
What Can Errors Contribute to Scientific Progress? ............................ 301
W. Haupt
Index ................................................................. 311
viii
Light as an Energy Source
and Information Carrier in
Plant Physiology
PHOTOSYNTHESIS: AN OVERVIEW.
Giorgio Forti
Centro di Studio CNR sulla Biologia Cellulare
e Molecolare delle Piante.
Dipartimento di Biologia dell'Universita di Milano,
Via Celoria 26, Milano, Italy.
INTRODUCTION
Oxygenic photosynthesis of green plants and cyanobacteria utilizes water as an electron
donor, light energy and CO2 to generate carbohydrates and other organic substances,
according to the overall equation :
(1)
The photochemical system involved, which is bound to the photosynthetic membranes
(the thylakoids) utilizes two photochemical reactions in series to transfer electrons against
the electrochemical gradient from H20 (Em= 810mY at pH 7) to the iron-sulphur protein
ferredoxin (Fd, Em= -420 mY at pH 7). Reduced ferredoxin is then utilized by a membrane
bound flavoprotein to reduce NADP (Em= -320 mY at pH 7). The electrochemical work of
1.23 ev is accomplished through the cooperation of two photochemical reactions. Electron
transport is coupled to the synthesis of ATP from ADP+Pi (inorganic OIthophosphate).
The stable products of photosynthetic electron transport ATP and NADPH are then
utilized to activate and reduce CO2 to the level of carbohydrates by a muItienzyme system
present as a dense protein solution in the stroma of the chloroplasts (or in the cytoplasm of
cyanobacteria) where the thylakoids are embedded. This latter process will not be discussed
in this paper, which is limited to the photochemical events and electron transport producing
NADPH and ATP.
In green plants, including the unicellular green eukariotes, the overall process of
photosynthesis is therefore accomplished within the chloroplast (see fig. 1), through the
cooperation of the events occurring within and on the surface of the thylakoids (light
absorption and excitation energy migration to the reaction centres, primary photochemical
reactions, electron transport and ATP synthesis) and those occurring in the stroma (C02
assimilation).
Light as an Energy Source and Information Carrier in Plant Physiology
Edited by Jennings et al.. PleI11Ull Press, New York, 1996
