http://biol.unt.edu/~rmittler/Papers/Reactive%20oxygen%20gene%20network%20of%20plants.pdf

Reactive oxygen gene network of plants

Drought-induced responses of photosynthesis and antioxidant metabolism in higher plants

Humans are unable to synthesise L-ascorbic acid (L-AA, ascorbate, vitamin C), and are thus entirely dependent upon dietary sources to meet needs. In both plant and animal metabolism, the biological functions of L-ascorbic acid are centred around the antioxidant properties of this molecule. Considerable evidence has been accruing in the last two decades of the importance of L-AA in protecting not only the plant from oxidative stress, but also mammals from various chronic diseases that have their origins in oxidative stress. Evidence suggests that the plasma levels of L-AA in large sections of the population are sub-optimal for the health protective effects of this vitamin. Until quite recently, little focus has been given to improving the L-AA content of plant foods, either in terms of the amounts present in commercial crop varieties, or in minimising losses prior to ingestion. Further, while L-AA biosynthesis in animals was elucidated in the 1960s, 1 it is only very recently that a distinct biosynthetic route for plants has been proposed. 2 The characterisation of this new pathway will undoubtedly provide the necessary focus and impetus to enable fundamental questions on plant L-AA metabolism to be resolved. This review focuses on the role of L-AA in metabolism and the latest studies regarding its bio- synthesis, tissue compartmentalisation, turnover and catabolism. These inter-relationships are considered in relation to the potential to improve the L-AA content of crops. Methodology for the reliable analysis of L-AA in plant foods is briefly reviewed. The concentrations found in common food sources and the effects of processing, or storage prior to consumption are discussed. Finally the factors that determine the bioavailability of L-AA and how it may be improved are considered, as well as the most important future research needs. # 2000 Society of Chemical Industry

Plant L‐ascorbic acid: chemistry, function, metabolism, bioavailability and effects of processing

It is now clear that hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H(2)O(2) generation, from a variety of sources. H(2)O(2) is removed from cells via a number of antioxidant mechanisms, both enzymatic and non-enzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H(2)O(2) and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H(2)O(2) and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.

Hydrogen peroxide and nitric oxide as signalling molecules in plants

Hydrogen peroxide (H 2 O 2 ) has been implicated in many stress conditions. Control of H 2 O 2 levels is complex and dissection of mechanisms generating and relieving H 2 O 2 stress is difficult, particularly in intact plants. We have used transgenic tobacco with ∼10% wild‐type catalase activity to study the role of catalase and effects of H 2 O 2 stress in plants. Catalase‐deficient plants showed no visible disorders at low light, but in elevated light rapidly developed white necrotic lesions on the leaves. Lesion formation required photorespiratory activity since damage was prevented under elevated CO 2 . Accumulation of H 2 O 2 was not detected during leaf necrosis. Alternative H 2 O 2 ‐scavenging mechanisms may have compensated for reduced catalase activity, as shown by increased ascorbate peroxidase and glutathione peroxidase levels. Leaf necrosis correlated with accumulation of oxidized glutathione and a 4‐fold decrease in ascorbate, indicating that catalase is critical for maintaining the redox balance during oxidative stress. Such control may not be limited to peroxisomal H 2 O 2 production. Catalase functions as a cellular sink for H 2 O 2 , as evidenced by complementation of catalase deficiency by exogenous catalase, and comparison of catalase‐deficient and control leaf discs in removing external H 2 O 2 . Stress analysis revealed increased susceptibility of catalase‐deficient plants to paraquat, salt and ozone, but not to chilling.

/pdf/catalase-is-a-sink-for-h2o2-and-is-indispensable-for-stress-2o9o35a49o.pdf

Catalase is a sink for H2O2 and is indispensable for stress defence in C3 plants.

A consequence of aerobic life is the formation of reactive forms of oxygen such as Superoxide radicals (O2•), hydrogen peroxide (H2O2), and hydroxyl radicals (OH•). In particular, hydroxyl radicals are one of the most reactive species known to chemistry, being able to react with DNA, proteins, lipids, and almost any other constituent of living cells (Halliwell, 1984). Its primary route of formation is thought to be an iron-catalyzed reaction of Superoxide radicals with hydrogen peroxide as follows

Oxidative Stress in Plants

A wide range of environmental stresses (such as chilling, ozone, high light, drought, and heat) can damage crop plants, with consequent high annual yield losses. A common factor in all these unrela...

/pdf/engineering-stress-tolerance-in-maize-2d724cz9rj.pdf

Marc Van Montagu

Papers

Oxidative Stress in Plants

Engineering Stress Tolerance in Maize

Engineering stress tolerance in maize.

Oxidative stress in plants

Oxidative Burst and the Role of Reactive Oxygen Species in Plant-pathogen Interactions