Drought tolerance in a Saharian plant Oudneya africana: Role of antioxidant defences

Drought is one of the most limiting factors for plant survival mainly in arid areas. The predicted increase of temperature and dryness due to climate change will exacerbate this problem in many areas throughout the world. In this work, we analyze the mechanism involved in drought tolerance in a Saharan plant, Oudneya africana, by using two different irrigation regimes, a time course analysis, as well as re-watering after drought. The content of hydrogen peroxide (H2O2), NO, lipid peroxidation, enzymatic and non-enzymatic antioxidants and NADPH sources in leaves was analyzed. Drought induces the accumulation of H2O2 and NO, being the highest rate observed under the most severe conditions. The glycolate oxidase (GOX; EC 1.1.3.1) from photorespiration has been demonstrated to be one of the most important sources of H2O2. Water deficit produces disturbances in enzymatic and non enzymatic antioxidants to cope with the increase of reactive oxygen accumulation and differentially affected the pattern of superoxide dismutases (SOD; EC 1.15.1.1) and peroxidases (POX). The analysis of principal component shows a positive and significant relationship between the redox status (GSH/GSSG; ASC/DHA), glutathione reductase (GR; EC 1.6.4.2), the malate dehydrogenase (MDH; EC 1.1.1.37) and NADP-depend isocitrate dehydoregenase (NADP-ICDH; EC 1.1.1. 42) under long term treatment, suggesting that tolerance of Oudneya under these conditions is mainly due to the ASC-GSH cycle efficiency. Under medium drought stress the higher correlation was observed between DHA, ASC and glutathione S-transferase (GST; EC 2.5.1.18), while during the rehydration period catalase (CAT; EC 1.11.1.6), H2O2, GOX, NO and guayacol peroxidase (GPX; EC 1.11.1.7) show a high correlation, suggesting an important role of peroxidases and photorespiration in the adjustment of metabolic pathways during drought recovery. These results also show that longer exposure to medium stress has a stronger effect than shorter periods at higher intensity. The results obtained in this work suggest that Oudneya has the ability to activate a complex antioxidative defense system involved in the drought tolerance regulation probably involving H2O2-dependent signals.