2008). Several studies correlated improved plant tolerance to abiotic stresses upon pathogenic or mutualistic microbial infections with an observed increase in antioxidant or osmolyte concentrations and/or in antioxidant enzymes activities (Rouhier and Jacquot 2008). This may explain the development of systemic acquired resistance in plants following pathogenic infections where healthy plant parts gain more resistance to a subsequent infection by either the same or another microbe (Singh et al. 2011). The root colonizing endophytic fungus Piriformospora indica was discovered in association with woody shrubs in the Indian Thar Salubrinal purchase desert and was found to improve plant fitness of a variety

of host plants by growth enhancement under normal and stress conditions (Verma et al. 1998; Schäfer et al. 2007). The fungus was reported to activate nitrate reductase

GSK1904529A cell line and glucan-water dikinase enzymes resulting in increased nitrate acquisition and/or starch degradation in Arabidopsis and tobacco roots (Sherameti et al. 2005). Further studies indicated involvement of cytokinins in P. indica induced growth promotion of Arabidopsis plants, while auxins had little or no effect (Vadassery et al. 2008). In addition to growth promotion, P. indica, originally isolated from desert plants, was found to induce drought stress tolerance of Arabidopsis and Chinese cabbage (Brassica rapa) by stimulation the expression of stress-related genes in leaves (Oelmüller et al. 2009; Sun et al. 2010). In Chinese cabbage colonized by P. indica the activities of peroxidases, catalases and superoxide dismutases in the leaves were increased within 24 h in response to drought see more stress. The fungus also increased the amount of chloroplast-localized Ca2+ sensing receptor protein, which regulates stomatal function in response to elevations of external Ca2+ by modulating

cytoplasmic Ca2+ concentration (Weinl et al. 2008; Sun et al. 2010). Furthermore, the drought induced decrease in photosynthetic efficiency and the degradation of chlorophylls and thylakoid proteins were delayed (Sun et al. 2010). P. indica also induced salt tolerance to a salt-sensitive barley cultivar (Hordeum vulgare) by increasing the rate of metabolic activity to EPZ5676 chemical structure compensate salt-induced inhibition of leaf metabolism (Criddle et al. 1989; Baltruschat et al. 2008), by induction of antioxidant enzymes (Baltruschat et al. 2008), and by enhancing the ratio of reduced to oxidized ascorbate (Waller et al. 2005). The latter neutralizes oxygen free radicals and acts as a primary substrate in the ascorbate-glutathione cycle to detoxify hydrogen peroxide (Foyer and Noctor 2000). It may also act by accelerating root elongation and increasing root biomass (Córdoba-Pedregosa et al. 2005). Furthermore, P. indica enhanced the biosynthesis of polyamines and lowered that of ethylene by increasing methionine synthase levels (Peškan-Berghöfer et al.