Ascorbate-Glutathione Pathway and Stress Tolerance in Plants

462 Pages·2010·5.46 MB·English

by  Dariusz Latowski

Ascorbate-Glutathione Pathway and Stress
Tolerance in Plants
w
Naser A. Anjum Shahid Umar Ming-Tsair Chan
● ●
Editors
Ascorbate-Glutathione
Pathway and Stress
Tolerance in Plants
Editors
Naser A. Anjum Shahid Umar
Centre for Environmental and Marine Department of Botany
Studies (CESAM) and Faculty of Science
Department of Chemistry Hamdard University
University of Aveiro New Delhi
3810–193 Aveiro India
Portugal [email protected]
[email protected]; [email protected]
Ming-Tsair Chan
Academia Sinica Biotechnology Center
in Southern Taiwan
Sinshih Township
Tainan County 74146
Taiwan
[email protected]
ISBN 978-90-481-9403-2 e-ISBN 978-90-481-9404-9
DOI 10.1007/978-90-481-9404-9
Springer Dordrecht Heidelberg London New York
Library of Congress Control Number: 2010934293
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To
A Great Philanthropist, Thinker, Visionary
&
The Founder of Jamia Hamdard
(Hamdard University), New Delhi, INDIA
Janab Hakeem Abdul Hameed
(1908–1999)
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Foreword
Anti-scorbutic factor (Vitamin C), ascorbic acid, was isolated from paprika by
A. Szent-Gyorgyi, and its anti-scorbutic effect was confirmed in guinea-pigs
(Biochem. J. 27: 278-285 (1933). Occurrence of anti-scorbutic factor in fruits,
vege tables and adrenal glands of vertebrates had been deduced from their protective
effects against scurvy. However, its isolation from either lemon or adrenal glands
was a very heavy work in 1920-30, which required several tons (!) of the materials
and several years, because of its low contents and disturbing components. In 1933,
Szent-Gyorgyi in Szeged, Hungary, established a simple way for preparation of 450 g
crystalline ascorbic acid within a month from local paprika (Hungarian red pepper,
Capscicum annuum). This isolation was initiated by his finding of high reducing
potentials in paprika juice, as deduced by disappearance of blue dibromophenolin-
dophenol. Even in the current data book on food nutrients, the content of vitamin
C in paprika is one of the highest ones among vegetables and fruits, indicating a
sharp sense of Szent-Gyorgyi focusing to paprika as the starting material for the
isolation of anti-scorbutic factor. In those days, a large amount of ascorbate was
required for the determination of its structure, which was accomplished by W.
Haworth in England. The revealed structure opened a gate to synthesize ascorbate,
which was soon done by W. Haworth and T. Reichstein, independently. Thus,
ascorbate is the first vitamin which is chemically synthesized.
Based on these works and the following many works and surveys on the antioxi-
dants in plants, World Cancer Research Fund (2007) recommended; “Eat at least
five servings (total at least 400 g) of a variety of non-starchy vegetables and of
fruits every day, to protect from cancer”, as one of the personal recommendations
for foods to escape from cancer. This is a very reasonable one considering that
plants are always exposed to most stressful environments among organisms; strong
sun light, highest oxygen concentration in leaf tissues, and low homeostasis in
respects of temperature and other environmental factors. Thus, plants are expected
to contain very effective antioxidants at high contents for survival under natural
environments, therefore, both vegetables and fruits are very rich in the antioxidants
which are able to protect DNA from ROS.
Even though ascorbate isolated from plants has contributed so much to under-
stand its nutritional effect for human, the physiological and biochemical functions
of ascorbate in plants themselves have remained obscure for many years. In plants,
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it had been supposed that ascorbate (AsA), with glutathione (GSH), plays a role as
general antioxidants as in animals. However, ascorbate-specific reaction or enzyme
in plants was not identified, except for ascorbate oxidase, up to 1980.
When chloroplasts are exposed to higher photon intensities over that required for
CO-fixation, excess photons induce the reduction of oxygen in place of CO.
2 2
Mehler found the photoproduction of HO in chloroplasts and then, in 1970s, this
2 2
HO is shown to be produced through the SOD-catalyzed disproportionation of
2 2
superoxide, which is the primary photoreduced product of oxygen in PS I (Asada).
Because even very low amounts of HO inactivate the CO-fixation enzymes, plant
2 2 2
chloroplasts should equip the effective scavenging system of HO. Chloroplasts do
2 2
not contain any catalase, then, peroxidase is a possible scavenger of HO. In 1980-
2 2
81, ascorbate-specific peroxidase (APX) was found in Euglena cells (Shigeoka et
al.) which do not contain catalase, and also in plant chloroplasts (Nakano and
Asada). Further, the regeneration of AsA from the oxidized ascorbates (monodehy-
droascorbate, MDHA radical & dehydroascorbate, DHA) by respective reductases
has been characterized including glutathione peroxidase (GPX) and glutathione
reductase (GR), all of them are required to scavenge ROS in chloroplasts. Thus,
ascorbate-glutathione (AsA-GSH) and related enzymes are essential to scavenge
effectively ROS generated in chloroplasts under environmental stress.
In addition to chloroplasts, APX and other related enzymes for either scavenging
or adjustment of ROS levels have been found in other cell organelles, such as mito-
chondria, peroxisomes, plasma membranes, apoplasts and other cell compartments.
Further, the superoxide-generating, plasma membrane-bound NADPH oxidase has
been found and plays a role in the generation for physiologically functional ROS.
These systems have an intimate relation with AsA-GSH, as in chloroplasts.
The present monograph, edited by eminent scientists Drs. Naser A. Anjum,
Shahid Umar and Ming-Tsair Chan, covers the current progress on the physiologi-
cally functional ROS, in relation to AsA-GSH. I believe that the revealed mecha-
nisms of signaling and other functions of ROS with intimate correlations of
AsA-GSH pathway in plants, and its further progress should contribute to under-
stand the ROS-signal systems in responses to under biotic and biotic stresses.
Further, they should provide the focusing points to be analyzed further to support
higher crop yields. Furthermore, the ROS-related signaling system mediate signal-
ing system mediated or adjusted by AsA-GSH system in plants should give a clue
to understand the similar systems for human health, as have been done since AsA
was isolated from paprika.
July 29th 2010 Kozi Asada
Kyoto University (Emeritus)
Kyoto, JAPAN
e-mail: [email protected]
Preface
Since last several decades, increasing agricultural productivity has been a challeng-
ing task to fulfill the requirements of enough food to feed rapidly increasing world
population in the changing environment. Both biotic and abiotic stress factors are
continued to negatively affect various aspects of plant growth and development
leading to relative decrease in the potential maximum yields by more than fifty
percent. These stress factors have been shown to affect various aspects of plant
system including the acceleration in the formation of reactive oxygen species
(ROS). Although, reactive oxygen species are important signal molecules that regu-
late plant responses to environmental stress factors but these must be rapidly pro-
cessed and/or detoxified if oxidative damage is to be averted in cells. The ascorbate
(AsA)-glutathione (GSH) pathway is a key part of the network of reactions involv-
ing enzymes and metabolites with redox properties for the detoxification of ROS,
and thus to avert the ROS-accrued oxidative damage in plants.
Both AsA and GSH are intimately linked in terms of their major physiological
functions in AsA-GSH pathway and many of these processes are correlated with
endogenous AsA-GSH levels especially under stress conditions. In addition to having
major role during vital phases of the plant life cycle, AsA and GSH determine the
lifetime of reactive oxygen species within the cellular environment and provide cru-
cial protection against oxidative damage. While research into the responses of indi-
vidual components of plant antioxidant defense system has benefited greatly from
advances in molecular technology, the cross-talks and inter-relationships studies on
the physiological, biochemical and molecular aspects of the cumulative response of
various components of AsA-GSH pathway to stress factors and their significance in
plant stress tolerance have received comparatively very little or no attention.
The present book has concentrated more on cumulative responses of the compo-
nents of AsA-GSH pathway in plant stress tolerance with emphasis on the unique
insights and advances gained by molecular exploration than whole plant antioxi-
dant defense system. In fact, these studies/reports based on inter-relationships and/
or cross-talks are expected to lead to understand and improve the mechanisms of
stress tolerance in plants. Therefore, the present volume would definitely be an
ideal source of scientific information to the advanced students, junior researchers,
faculty and scientists involved in agriculture, plant sciences, molecular biology,
biochemistry, biotechnology and related areas.
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