Responses of Antioxidative Systems to Drought Stress in Pendunculate Oak and Maritime Pine as Modulated by Elevated CO2

Abstract

The aim of the present study was t o investigate the effects of an enhanced CO, concentration alone or in combination with drought stress on antioxidative systems of a deciduous (oak; Quercus robur) and an evergreen (pine; Pinos pinaster) tree species. The seedlings were grown for one season in a greenhouse in tunnels supplied with 350 or 700 p L L-' CO,. The experiment was repeated i n a second year. Antioxidants, protective enzymes, soluble protein, and pigments showed considerable fluctuations in different years. Elevated CO, caused significant reductions in the activities of superoxide dismutases i n both oak and pine. The activities of ascorbate peroxidase and catalase were also reduced in most cases. The activities of dehydroascorbate reductase, monodehydroascorbate radical reductase, glutathione reductase, and guaiacol peroxidase were affected little or not at all by elevated CO,. When the trees were subjected to drought stress by withholding water, the activities of antioxidative enzymes decreased in leaves of pine and oak grown at ambient CO, and increased in plants grown at elevated CO, concentrations. The present results suggest that growth i n elevated CO, might reduce oxidative stress to which leaf tissues are normally exposed and enhance metabolic flexibility t o encounter increased stress by increases in antioxidative capacity.Most predictions suggest that the current mean ambient CO, concentration of 355 pL L-' will approximately double by the end of the next century (Roeckner, 1992). Increasing concentrations of CO, and of other greenhouse gases will result in an increase in mean temperature and cause changes in precipitation patterns (Roeckner, 1992). Climate models predict large-scale drought periods during summer for northern mid-latitudes (Roeckner, 1992). The availability of water is one of the most important factors determining vegetation diversity and plant productivity (Rochefort and Woodward, 1992). The effects of water deficits on plant performance and growth are mediated through decreases in stomatal conductance and photosynthesis and depend on the severity and duration of the drought period, the '

Field investigations of nitrogen dioxide (NO<sub>2</sub>) exchange between plants and the atmosphere

“…Previous studies suggest that mesophyllic characteristics like leaf ascorbate concentration may influence NO 2 exchange rates (Ramge et al, 1993;Teklemariam and Sparks, 2006). The apoplastic ascorbate concentration varies with species, environmental conditions (Polle et al, 1995;Schwanz et al, 1996) and stage of development (Luwe, 1996). Another reason could be a different colonization of the trees by chemolithoautotrophic nitrifying bacteria.…”

NH3 and NO2 fluxes between beech trees and the atmosphere – correlation with climatic and physiological parameters

“…Since disproportionation of NO # in water is thought to be slow at atmospheric NO # concentrations (Lee & Schwartz, 1981 ;Norby et al, 1989 ;Ramge et al, 1993), the reaction with apoplastic ascorbate might be of particular significance for maintaining a high flux of NO # into the leaves, and might prevent internal resistances. The apoplastic ascorbate concentration, however, is supposed to vary considerably between species (Polle et al, 1990Luwe, 1996 ;Schwanz et al, 1996a) and might depend on environmental factors (Polle & Rennenberg, 1992 ;Polle et al 1995 ;Schnug et al, 1995 ;Schwanz et al, 1996a, b) and\or stage of development (Luwe, 1996). Further experiments are required to correlate differences in internal resistances with apoplastic ascorbate concentrations.…”

Water stress induces overexpression of superoxide dismutases that contribute to the protection of cowpea plants against oxidative stress

“…Furthermore, it is often assumed that SOD activity determines O 2 .-concentration (Schwanz et al, 1996). According to the relation:…”