Abstract
Water stress is known to induce active oxygen species in plants. The accumulation of these harmful species must be prevented by plants as rapidly as possible to maintain growth and productivity. The aim of this study was to determine the effect of water stress on superoxide dismutase isozymes (SOD, EC 1.15.1.1.) in two cowpea cultivars [Vigna unguiculata L. Walp., cv. Bambey 21 (B21) and cv. TN88- 63]. Plants were submitted to water stress by withholding water supply and the expression of SOD was characterized during stress induction. In the same time, photosynthesis characteristics were determined through the measurement of the quantum yield of PS II photochemistry and the energy absorption rate per reaction centre. Results show how water stress regulates the synthesis and the activity of superoxide dismutase isoforms and how these enzymes contribute to protect photosynthesis against the damageable effects of superoxide radicals in cowpea. Increased MnSOD and FeSOD activity and concentration were shown to be induced by water stress and associated with protection of photosystem II photochemistry and whole plant growth against oxidative stress in these plants. On the contrary, plants unable to express high MnSOD and/or FeSOD isoforms showed more sensitivity to water stress.
Highlights
The most feared and widespread plant stress agents are active oxygen species
We point out superoxide dismutase (SOD) isoforms in cowpea cultivars, and we study their activity during water stress induction
Variations of PS photosystem II (II) photochemistry and regulation of SOD activities were studied in two cowpea cultivars under water stress conditions
Summary
The most feared and widespread plant stress agents are active oxygen species These include redox intermediates in the reduction and oxidation between dioxygen and water; superoxide anion (O2.-), hydrogen peroxide (H2O2) and hydroxyl radical (HO.), and the electronically-excited oxygen species, singlet excited oxygen. These species are able to react with DNA, lipids, proteins, and almost any other constituent of plant or animal cells (Beauchamp and Fridovich, 1971; Demming and Björkman, 1987; Halliwell and Gutteridge, 1989). These reduced oxygen species are generated as by-products of endogenous biological reactions, and their formation increases during biotic and abiotic stresses. The three known types of this enzyme can be distinguished according to their metal cofactor made of manganese (MnSOD), iron (FeSOD) or copper and zinc (Cu/Zn SOD) (Bannister et al, 1987), and according to their be-
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