The present study was carried out to study the effect of salt stress on cell membrane damage, ion content and antioxidant enzymes in wheat (Triticum aestivum) seedlings of two cultivars salt-tolerant KRL-19 and salt-sensitive WH-542. Seedlings (4-d-old) were irrigated with 0, 50 and 100 mM NaCl. Observations were recorded on the 3 rd and 6 th day after salt treatment and 2 nd day after salt removal. The relative water content declined with induction of salt stress, more in WH-542 than in cv. KRL-19. K + /Na + ratio in KRL-19 was higher than in WH-542. WH-542 suffered greater damage to cellular membranes due to lipid peroxidation as indicated by higher accumulation of H 2 O 2 , MDA and greater leakage of electrolytes than KRL-19. The activities of catalase, peroxidase and ascorbate peroxidase and glutathione reductase increased with increase in salt stress in both the cultivars, however, superoxide dismutase activity declined. Upon desalanization, partial recovery in the activities of these enzymes was observed in KRL-19 and very slow recovery in WH-542.Additional key words: ascorbate peroxidase, calatase, glutathione reductase, hydrogen peroxide, malondialdehyde, peroxidase, superoxide dismutase, Triticum aestivum.

Chickpea plants were subjected to salt stress for 48 h with 100 mM NaCl, after 50 days of growth. Other batches of plants were simultaneously treated with 0.2 mM sodium nitroprusside (NO donor) or 0.5 mM putrescine (polyamine) to examine their antioxidant effects. Sodium chloride stress adversely affected the relative water content (RWC), electrolyte leakage and lipid peroxidation in leaves. Sodium nitroprusside and putrescine could completely ameliorate the toxic effects of salt stress on electrolyte leakage and lipid peroxidation and partially on RWC. No significant decline in chlorophyll content under salt stress as well as with other treatments was observed. Sodium chloride stress activated the antioxidant defense system by increasing the activities of peroxidase (POX), catalase (CAT) superoxide dismutase (SOD) and ascorbate peroxidase (APX). However no significant effect was observed on glutathione reductase (GR) and dehydro ascorbate reductase (DHAR) activities. Both putrescine and NO had a positive effect on antioxidant enzymes under salt stress. Putrescine was more effective in scavenging superoxide radical as it increased the SOD activity under salt stress whereas nitric oxide was effective in hydrolyzing H 2 O 2 by increasing the activities of CAT, POX and APX under salt stress.

No abstract

Accumulation of salts in irrigated soils is one of the primary factors limiting yield in South Asia. We investigated whether exogenous nitric oxide (NO) supplementation as sodium nitroprusside has any ameliorating effect against NaCl induced oxidative damage in chickpea leaves. NaCl treatment (250 mM) alone and in combination with two concentrations of SNP (0.2 and 1 mM) were given to 50 days old chickpea plants for 2, 4 and 6 days. Salt stress adversely affected the relative membrane injury, lipid peroxidation levels, relative water content (RWC) and H 2 O 2 content. The effect was time dependent. SNP treatments could ameliorate the toxic effect of short term salt stress of 2 days on relative membrane injury and partial amelioration was observed with 4 and 6 day stress treatment. A partial ameliorative effect of SNP was observed with lipid peroxidation levels, H 2 O 2 content and RWC. Salt stress activated the antioxidant system by increasing the activities of SOD, POX, APX and DHAR. However no obvious change was observed in GR activity and CAT activity decreased under salt stress. Both the SNP treatments had a positive effect on antioxidant enzymes SOD, CAT, APX, GR and DHAR under salt stress. NaCl treatment resulted in a decline in the GSH/GSSG and ASC/DHA ratio. SNP treatments increased the reduced form of both the metabolites thus elevating the ratio of GSH/GSSG and ASC/DHA. This study concludes that exogenous application of NO protects chickpea leaves from NaCl induced oxidative stress.

No abstract

A membrane-bound, sulphide-linked nitrite reductase from Thiobacillus denitrz3cans was solubilized and after further purification its properties were examined. The purified enzyme, mol. wt 120000, contained cytochromes c and din the ratio of 1 : 1. Both cytochromes were reduced by sulphide and re-oxidized with nitrite or air. Oxidation by nitrite resulted in the appearance of an absorption peak at 572 nm. The kinetics of the reduction of the enzyme with sulphide indicated that cytochrome c was reduced before cytochrome d. The redox potential of cytochrome d was 22 mV more positive than that of cytochrome c. Cytochromes c and d were dissociated from the purified enzyme by treatment with sodium dodecyl sulphate. The purified nitrite reductase also had cytochrome oxidase activity and both the activities were stimulated by cytochrome c-55 1 isolated from T. denitriJicans. Reduced cytochrome c-551 was an effective electron donor for the purified enzyme with either nitrite or air as the terminal electron acceptor. Neither cytochrome c-554 (also isolated from T. denitrzjicans) nor mammalian cytochrome c was effective as reductant for the enzyme. NO and N 2 0 were identified as the products of nitrite reduction by the purified sulphidelinked nitrite reductase.

No abstract

A membrane-bound nitrate reductase from Thiobacillus denitrificans can utilize either sulphite or NADH as an electron donor. The sulphite-dependent nitrate reductase activity was released from the membrane by treatment with sodium deoxycholate. Cytochrome c and FAD were separated from the solubilized enzyme by heat treatment and subsequent chromatography on DEAE-cellulose. The bacterial cytochrome c and a preparation of horse-heart cytochrome c served as electron mediators to the solubilized sulphite-dependent nitrate reductase activity with apparent K,, values of I -5 and I -3 ,UM respectively. The NADH-linked enzymic activity, which was unstable during storage, was re-activated with reduced glutathione. It was also inactivated after treatment with deoxycholate but this effect was reversed by menadione. A possible scheme for electron transport for the sulphite-and NADH-dependent enzyme is proposed.