Salt stress induces altered expression of genes encoding antioxidant enzymes in seedlings of a Brazilian indica rice (Oryza sativa L.)

Antioxidant defenses have evolved to protect cells from the potential hazardous effects of reactive oxygen species (ROS). In plants, unfavorable environmental conditions such as salt stress lead to increased production and accumulation of ROS. To access the effect of salinity on rice, a major crop in Brazil and the world, we analyzed the responses of transcripts corresponding to antioxidant enzymes in a Brazilian indica cultivar upon NaCl stress in two different developmental stages. In 11-day-old seedlings, APx, CatB, GR, SodCc1, and SodCc2 were up-regulated, while CatA, CatC, and GPx remained unaltered. In 6-week-old plants, higher mRNA levels were observed for CatB, GR, and SodCc2. Salt had no significant effect on APx, GPx, and SodCc1. Furthermore, in 6-week-old plants CatA and CatC displayed diurnal oscillations, cycling in opposite phases. Although cycling was. not disrupted by salt, CatA accumulation was significantly impaired. Several putative cis-elements involved in light regulation were identified by in silico analysis of both promoters. We propose a circadian clock control for CatC, similar to CatA. Our results show that salt triggered a differential modulation of antioxidant transcripts, possibly due to disruption of cell redox homeostasis. (C) 2003 Elsevier Ireland Ltd. All rights reserved.