Antioxidant responses of rice seedlings to salinity stress
Introduction
Salinity in soil or water is of increasing importance to agriculture because it causes a stress condition to crop plants. Particularly for rice (Oryza sativa L.), a species native to swamps and freshwater marshes, secondary salinization is becoming an increasingly serious production constraint [1]. Because of the inherent sensitivity of rice plant to salt stress [2], there has been a great interest in developing varieties that are resistant to salinity. Defining salt tolerance, however, is quite difficult because of the complex nature of salt stress and the wide range of plant responses.
One of the biochemical changes possibly occurring when plants are subjected to harmful stress conditions is the production of activated oxygen species. The chloroplasts and mitochondria of plant cells are important intracellular generators of activated oxygen species. Electrons leaked from electron transport chains can react with O2 during normal aerobic metabolism to produce activated oxygen species such as superoxide (O2−), hydrogen peroxide (H2O2), and the hydroxyl radical (OH). Singlet oxygen (1O2) can also be produced through the energetic activation of ground state oxygen. These cytotoxic oxygen species are highly reactive and in the absence of any protective mechanism they can seriously disrupt normal metabolism through oxidative damage to lipids, protein and nucleic acids 3, 4. Fortunately plants possess a number of antioxidant enzymes that protect them against the damaging effects of activated oxygen species. Superoxide dismutase (SOD; EC1.15.1.1) is a major scavenger of O2−, and its enzymatic action results in the formation of H2O2 and O2. The hydrogen peroxide produced is then scavenged by catalase (EC 1.11.1.6) and a variety of peroxidases (EC 1.11.1.7). Catalase, which is apparently absent in the chloroplast, dismutates H2O2 into water and molecular oxygen, whereas peroxidase decomposes H2O2 by oxidation of co-substrates such as phenolic compounds and/or antioxidants.
This study was designed to determine, aside from growth, the effect of salt stress on antioxidant enzyme activities, lipid membrane peroxidation, electrolyte leakage and Na+ content of leaves of rice varieties exhibiting differences in salinity tolerance. Comparison of these responses could be useful in identifying differences related to the relative ability of each cultivar to cope with salinity. Results from this study can supply information on the possible involvement of activated oxygen species in the mechanism of damage by NaCl stress in rice plant, and also could allow deeper insights into the molecular mechanisms of tolerance to salt-induced oxidative stress.
Section snippets
Plant materials and salinity treatments
Four rice varieties differing in salt tolerance and being categorized into two ecogeographic landraces were used. The japonica landraces were Hitomebore (salt-sensitive) and Bankat (salt-tolerant) while the indica landraces comprised IR28 (salt-sensitive) and Pokkali (salt-tolerant). Seeds of each variety were sown individually in holes of a styrofoam board with a nylon net bottom (54 seeds of one genotype to an area of 200×300 mm constituted a site). The styrofoam boards were then floated on
Effect of salinity on growth
Based on shoot dry weight, the relative growth rates of the four O. sativa varieties subjected to 1-week salinity treatments are shown in Fig. 1. Varieties which are considered as salt-tolerant, that is, Bankat and Pokkali, showed higher growth rate values at 6 dS m−1 salinity level compared to the non-salt-treated plants. The salt-sensitive varieties, Hitomebore and IR28, on the other hand, did not show this growth stimulation at moderate salinity level. At 12 dS m−1 salinity level, all of the
Discussion
Considerable effort has been exerted in the selection and development of rice varieties resistant to salinity stress. Progress, however, seems slow primarily due to inadequate understanding of the mechanism of salt tolerance.
In rice, as well as in other crops, agronomic characteristics, such as survival, yield, leaf damage and plant height are the most commonly used criteria for measuring salt tolerance 11, 12. This is probably due to their ease of measurement and the fact that yield under
Acknowledgements
The authors wish to thank Drs Takaharu Hayashi and Shigeo Yashima, present and former head of the International Collaboration Research Section, respectively, for their managerial support. This work was undertaken when the first author was granted a Visiting Research Fellowship at the Okinawa Subtropical Station, Japan International Research Center for Agricultural Sciences, Ministry of Agriculture, Forestry and Fisheries, Japan.
References (33)
Protein damage and degradation by oxygen radicals I. General aspects
J. Biol. Chem.
(1987)Biological effects of the superoxide radical
Arch. Biochem. Biophys.
(1986)- et al.
Superoxide dismutase: improved assays and an assay applicable to acrylamide gels
Anal. Biochem.
(1971) - et al.
Assay of catalase and peroxidases
Methods Enzymol.
(1955) - et al.
Changes in soluble and cell wall-bound peroxidase activities with growth in anoxia-treated rice (Oryza sativa L.) coleoptiles and roots
Plant Sci.
(1995) A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding
Anal. Biochem.
(1976)- et al.
Effect of salinity (NaCl) stress on H2O2 metabolism in Vigna and Oryza seedlings
Biochem. Physiol. Pflanzen.
(1990) - et al.
Salt-induced oxidative stress in chloroplasts of pea plants
Plant Sci.
(1995) - et al.
Response of melon plants to salt. I. Growth, morphology and root membrane properties
J. Plant Physiol.
(1991) - et al.
Peroxidase-regulated elongation of segments from peanut hypocotyls
Plant Sci.
(1992)
Saline soil of South and Southeast Asia as potential rice lands
Crop response and management on salt-affected soils
Rice culture method for experiment III. Laboratory scale culture of rice
Plant Cell Tech.
Lipid peroxidation associated with accelerated aging of soybean axes
Plant Physiol.
Changes in plant response to NaCl during development of rice (Oryza sativa L.) varieties differing in salinity resistance
J. Exp. Bot.
Screening of rice (Oryza sativa L.) genotypes for physiological characters contributing to salinity resistance, and their relationship to overall performance
Theor. Appl. Genet.
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Present address: Environmental Resources Division, JIRCAS, Tsukuba, Ibaraki 305, Japan.