Hydrogen peroxide- and nitric oxide-induced systemic antioxidant prime-like activity under NaCl-stress and stress-free conditions in citrus plants

We tested whether pre-treatments of roots with H2O2 (10 mM for 8 h) or sodium nitroprusside (SNP; 100 mu M for 48 h), a donor of (NO)-N-center dot, could induce prime antioxidant defense responses in the leaves of citrus plants grown in the absence or presence of 150 mM NaCl for 16 d. Both root pre-treatments increased leaf superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities, and induced related-isoform(s) expression under non-NaCl-stress conditions. When followed by salinity, certain enzymatic activities also exhibited an up-regulation in response to H2O2 or SNP pre-exposure. An NaCl-stress-provoked decrease in the ascorbate redox state was partially prevented by both pre-treatments, whereas the glutathione redox state under normal and NaCl-stress conditions was increased by SNP. Real-time imaging of (NO)-N-center dot production was found in vascular tissues and epidermal cells. Furthermore, NaCl-induced inhibition in (OH)-O-center dot scavenging activity and promotion of (OH)-O-center dot-mediated DNA strand cleavage was partially prevented by SNP. Moreover, NaCl-dependent protein oxidation (carbonylation) was totally reversed by both pre-treatments as revealed by quantitative assay and protein blotting analysis. These results provide strong evidence that H2O2 and (NO)-N-center dot elicit long-lasting systemic primer-like antioxidant activity in citrus plants under physiological and NaCl-stress conditions. (C) 2009 Elsevier GmbH. All rights reserved.