Response of antioxidant systems and leaf water relations to NaCl stress in pea plants

Abstract

A pea (Pisum sativum cv. Puget) cultivar was grown on a medium containing different NaCl concentrations (0-160 mol m −$ ) in order to study the effects of salt stress on leaf water relations and on the activity of antioxidant enzymes. NaCl stress caused a rapid decline in chlorophyll content. Both leaf water (ψ l ) and osmotic potentials (ψ s ) decreased progressively with the severity of the stress (from 90-160 mol m −$ NaCl) whereas leaf turgor pressure (ψ p ) increased in treated plants. Pea leaves contained an iron-containing superoxide dismutase (Fe-SOD) isozyme in chloroplasts alongside a copper-zinc-containing (CuZn-SOD) form (CuZn-SOD II). The lowest NaCl concentration (70 mol m −$ ) had no effect on the activity of these antioxidant enzymes while higher concentrations (110-130 mol m −$ ) enhanced the activity of cytosolic CuZn-SOD I and chloroplastic CuZn-SOD II as well as that of mitochondrial and\or peroxisomal manganese-containing superoxide dismutase (Mn-SOD). These inductions were matched by increases in the activity of ascorbate peroxidase (APX) and monodehydroascorbate reductase (MDHAR). The increased activities coincided with decreased stomatal conductance and were unaffected by the severity of stress except in the case of CuZn-SOD II which fell to control values under the highest stress conditions (140-160 mol m −$ NaCl), when a concomitant increase in chloroplastic Fe-SOD activity was observed. Glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities were only induced under severe NaCl stress (130-160 mol m −$ ) and were accompanied by losses in the ascorbate and glutathione pools, lower ASC\DHA and GSH\GSSG ratios and increases in GSSG. Electron microscopy showed that the thylakoidal structure of the chloroplasts became disorganized and their starch content decreased in plants treated with 160 mol m −$ NaCl. Overall, the results suggest that salt stress is accompanied by oxidative stress, perhaps at the cell compartment level. The capacity of Puget cultivar to ensure cell turgor and to enhance the activity of enzymes involved in the defence against oxidative stress seems to be important in determining adaptation to moderate NaCl stress conditions. In plants exposed to severe NaCl stress (130-160 mol m −$ ) it seems that such resistance to oxidative stress is overcome, which might contribute to the deleterious effects of salt and significant growth reduction in these conditions.

Overexpression of AtMYB44 Enhances Stomatal Closure to Confer Abiotic Stress Tolerance in Transgenic Arabidopsis

“…Several AGPs were up-regulated in salt-treated 35S:AtMY44 plants, supporting observations that salt stress severely affects the maintenance of cell wall structure in seedling roots and ABA-induced seed dormancy (Van Hengel and Roberts, 2003;Lamport et al, 2006). Altered expression of several types of genes encoding chlorophyll biosynthetic enzymes, chlorophyll-binding proteins, thylakoid proteins, and other chloroplast-related proteins might be correlated with salt-induced chlorophyll disorganization and degradation (chlorosis; Hernandez et al, 1999). Enhanced expression of genes encoding subunits of magnesium-protoporphyrin-IX chelatase (Mg-chelatase), including CHLH, was also notable.…”

Effect of Potassium Levels on Antioxidant Enzymes and Malondialdehyde Content under Drought Stress in Sunflower (Helianthus annuus L.)

“…Being toxic for cells, AOS are efficiently eliminated by nonenzymatic (α-tocopherol, β-carotene, phenolic compounds, ascorbate, glutathione) and enzymatic antioxidants (Noctor and Foyer, 1998;Smirnoff, 1993 (Hegedus et al, 2001;Scandalios, 1993). H 2 O 2 is eliminated by various antioxidant enzymes such as catalases (CAT: EC 1.11.1.6) (Hernandez et al, 1999;Kono and Fridovich, 1983;Scandalios, 1993) and peroxidases (POX: EC 1.11.1.7) (Gara et al, 2003;Jablonski and Anderson, 1982) which convert H 2 O 2 to water. Other enzymes that are very important in the ROS scavenging system and function in the ascorbate-glutathione cycle are glutathione reductase (GR: EC 1.6.4.2), monodehydro ascorbat reductase (MDHAR: EC 1.6.5.4) and dehydroascorbate reductase (DHAR: EC 1.8.5.1) (Candan and Tarhan, 2003;Yoshimura et al, 2000).…”

Response of salt stressed barley seedlings to phenylurea

“…Saline (NaCl) stress in barley seedlings causes an increase in total phenolic compounds, flavonoids and enhancement of peroxidase and indoleacetic acid oxidase activities and consequent decrease in growth rate. The adverse effect of salt stress on germination, antioxidant enzymes, phenolic compounds, flavonoids can partially be rectified by phenylurea.Keywords: barley; phenylurea; salt stress; antioxidant enzymes; polyphenol oxidase; peroxidase; indoleacetic acid oxidase; phenolic compounds; flavonoids Environmental stresses are thought to result in the production of active oxygen in plant species, causing oxidative stress (Smirnoff 1993, Gossett et al 1994, Hernandez et al 1999). The ability of higher plants to scavenge the toxic active oxygen seems to be a very important determinant of their tolerance to environmental stress.…”

“…Environmental stresses are thought to result in the production of active oxygen in plant species, causing oxidative stress (Smirnoff 1993, Gossett et al 1994, Hernandez et al 1999). The ability of higher plants to scavenge the toxic active oxygen seems to be a very important determinant of their tolerance to environmental stress.…”