Reactive oxygen species and antioxidant machinery in abiotic stress tolerance in crop plants

To cope with environmental fluctuations and to prevent invasion by pathogens, plant metabolism must be flexible and dynamic. Active oxygen species, whose formation is accelerated under stress conditions, must be rapidly processed if oxidative damage is to be averted. The lifetime of active oxygen species within the cellular environment is determined by the antioxidative system, which provides crucial protection against oxidative damage. The antioxidative system comprises numerous enzymes and compounds of low molecular weight. While research into the former has benefited greatly from advances in molecular technology, the pathways by which the latter are synthesized have received comparatively little attention. The present review emphasizes the roles of ascorbate and glutathione in plant metabolism and stress tolerance. We provide a detailed account of current knowledge of the biosynthesis, compartmentation, and transport of these two important antioxidants, with emphasis on the unique insights and advances gained by molecular exploration.

ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control

Reactive oxygen species (ROS) are produced as a normal product of plant cellular metabolism. Various environmental stresses lead to excessive production of ROS causing progressive oxidative damage and ultimately cell death. Despite their destructive activity, they are well-described second messengers in a variety of cellular processes, including conferment of tolerance to various environmental stresses. Whether ROS would serve as signaling molecules or could cause oxidative damage to the tissues depends on the delicate equilibrium between ROS production, and their scavenging. Efficient scavenging of ROS produced during various environmental stresses requires the action of several nonenzymatic as well as enzymatic antioxidants present in the tissues. In this paper, we describe the generation, sites of production and role of ROS as messenger molecules as well as inducers of oxidative damage. Further, the antioxidative defense mechanisms operating in the cells for scavenging of ROS overproduced under various stressful conditions of the environment have been discussed in detail.

https://downloads.hindawi.com/archive/2012/217037.pdf

Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Photoreduction of dioxygen in photosystem I (PSI) of chloroplasts generates superoxide radicals as the primary product. In intact chloroplasts, the superoxide and the hydrogen peroxide produced via the disproportionation of superoxide are so rapidly scavenged at the site of their generation that the active oxygens do not inactivate the PSI complex, the stromal enzymes, or the scavenging system itself. The overall reaction for scavenging of active oxygens is the photoreduction of dioxygen to water via superoxide and hydrogen peroxide in PSI by the electrons derived from water in PSII, and the water-water cycle is proposed for these sequences. An overview is given of the molecular mechanism of the water-water cycle and microcompartmentalization of the enzymes participating in it. Whenever the water-water cycle operates properly for scavenging of active oxygens in chloroplasts, it also effectively dissipates excess excitation energy under environmental stress. The dual functions of the water-water cycle for protection from photoinihibition are discussed.

THE WATER-WATER CYCLE IN CHLOROPLASTS: Scavenging of Active Oxygens and Dissipation of Excess Photons

OXIDATIVE STRESS . . . . . . . . . . . . . .. . . . . .... . . . . .. . . . . .. . . . ... .. . . . . .... . . .. .. . . . . . ... . 84 RESPONSE OF SOD TO ENVIRONMENTAL STRESS . . . . . . . . . . . . . . . .. . . . .... . . .... . . . . . . 87 Photoinhibition . . . . . . . . . . .. . ... . . .. . . . .. . . . . ..... . . . , ... ", , ... ,' , ... . ,., . . . "" . .. . ,'.' . . ,' . . . . , ., 87 Paraquat and Other Herbicides . . .. , . . .... , ..... , . . . . ... . . . .. . . . . . . . . . . . . ,.. 91 Atmospheric Pollutants . . " .... , .... , " .... " , , . . , .... , ' 94 Waterlogging and Drought .. ", . . ... , . . . . . . , .. "", . . ", . . . . . ", . . . .. ", . . .. , . . . ... """", . . " 97 The Defense Response to Pathogens . ... . . . . "" ... "" .... " ...... " ,."" .... . , 98 The Phenomenon of Cross-Tolerance . . . , , .. . . . . ...... . . , . . . . . . , . . .... , .. . . . . . . . .. .. 101 The Mechanism of SOD Regulation ........ , , ...... , " 102 GENETIC ENGINEERING OF SOD IN PLANTS .. ' ...... ' . . . . . . . . . . . . . . . . . . . . . . . .. . . . , .... ' 104 Cu/ZnSOD and MnSOD Overexpression . . . . . .. . . . . . , . . . . . . .. . . . . . .. . . . . . , .... . . . . .. . . ,.... . . 105 Prospects for Stress Tolerance through Genetic Engineering of SOD . . . . ,,, .. , . . . . . . . 106

Superoxide dismutase and stress tolerance

Enhanced Tolerance to Photooxidative Stress of Transgenic Nicotiana tabacum with High Chloroplastic Glutathione Reductase Activity

The cellular polyamines putrescine, spermidine, and spermine are ubiquitous in nature and have been implicated in a wide range of growth and developmental processes. There is little information, however, on mutant plants or animals defective in the synthesis of polyamines. The Arabidopsis genome has two genes encoding spermidine synthase, SPDS1 and SPDS2. In this paper, we describe T-DNA insertion mutants of both of these genes. While each mutant allele shows normal growth, spds1-1 spds2-1 double-mutant seeds are abnormally shrunken and they have embryos that are arrested morphologically at the heart-torpedo transition stage. These seeds contain significantly reduced levels of spermidine and high levels of its precursor, putrescine. The embryo lethal phenotype of spds1-1 spds2-1 is complemented by the wild-type SPDS1 gene. In addition, we observed a nearly identical seed phenotype among an F2 seed population from the cross between the spds2-1 allele and SPDS1 RNA interference transgenic lines. These data provide the first genetic evidence indicating a critical role of the spermidine synthase in plant embryo development.

Spermidine Synthase Genes Are Essential for Survival of Arabidopsis

Employing classical two-dimensional electrophoresis (2-DE), amino acid sequencing and immunoblot analysis, we examine for the first time the effect of ozone, a highly notorious environmental pollutant, on rice seedling proteins. Drastic visible necrotic damage to leaf by ozone and consequent increase in ascorbate peroxidase protein(s) was accompanied by rapid changes in the 2-DE protein profiles, over controls. Out of a total of 56 proteins investigated, which were reproducible in repeated experiments, 52 protein spots were visually identified as differentially expressed over controls. Six proteins were N-terminally blocked, and the sequence of 14 proteins could not be determined, whereas 36 proteins were N-terminally and one was internally sequenced. Ozone caused drastic reductions in the major leaf photosynthetic proteins, including the abundantly present ribulose-1, 5-bisphosphate carboxylase/oxygenase, and induction of various defense/stress related proteins. Most prominent change in leaves, within 24 h post-treatment with ozone, was the induced accumulation of a pathogenesis related (PR) class 5 protein, three PR 10 class proteins, ascorbate peroxidase(s), superoxide dismutase, calcium-binding protein, calreticulin, a novel ATP-dependent CLP protease, and an unknown protein. Present results demonstrate the highly damaging effect of ozone on rice seedlings at the level of the proteome.

Proteome analysis of differentially displayed proteins as a tool for investigating ozone stress in rice (Oryza sativa L.) seedlings.

Chitosan activates defense/stress response(s) in the leaves of Oryza sativa seedlings

To better understand the role of active oxygen species (AOS) in acquired resistance to increased levels of ultraviolet (UV)-B irradiation in plants, we isolated an Arabidopsis mutant that is resistant to methyl viologen, and its sensitivity to UV-B was investigated A complementation test revealed that the obtained mutant was allelic to the ozone-sensitive radical-induced cell death1-1 (rcd1-1) Therefore, this mutant was named rcd1-2 rcd1-2 was recessive and nearly 4-fold more resistant to methyl viologen than wild type It exhibited a higher tolerance to short-term UV-B supplementation treatments than the wild type: UV-B-induced formation of cyclobutane pyrimidine dimers was reduced by one-half after 24 h of exposure; the decrease in quantum yield of photosystem II was also diminished by 40% after 12 h of treatment Furthermore, rcd1-2 was tolerant to freezing Steady-state mRNA levels of plastidic Cu/Zn superoxide dismutase and stromal ascorbate peroxidase were higher in rcd1-2 than in wild type, and the mRNA level of the latter enzyme was enhanced by UV-B exposure more effectively in rcd1-2 UV-B-absorbing compounds were more accumulated in rcd1-2 than in wild type after UV-B exposure for 24 h These findings suggest that rcd1-2 methyl viologen resistance is due to the enhanced activities of the AOS-scavenging enzymes in chloroplasts and that the acquired tolerance to the short-term UV-B exposure results from a higher accumulation of sunscreen pigments rcd1 appears to be a mutant that constitutively shows stress responses, leading to accumulation of more pigments and AOS-scavenging enzymes without any stresses

Hikaru Saji

Papers

Enhanced Tolerance to Photooxidative Stress of Transgenic Nicotiana tabacum with High Chloroplastic Glutathione Reductase Activity

Spermidine Synthase Genes Are Essential for Survival of Arabidopsis

Proteome analysis of differentially displayed proteins as a tool for investigating ozone stress in rice (Oryza sativa L.) seedlings.

Chitosan activates defense/stress response(s) in the leaves of Oryza sativa seedlings

A Methyl Viologen-Resistant Mutant of Arabidopsis, Which Is Allelic to Ozone-Sensitive rcd1, Is Tolerant to Supplemental Ultraviolet-B Irradiation