HYDROGEN PEROXIDE-ASSOCIATED AND GLUTATHIONE-ASSOCIATED MECHANISMS OFACCLIMATORY STRESS TOLERANCE AND SIGNALING

Plants adapt to environmental stresses through specific genetic respon ses. The molecular mechanisms associated with signal transduction, lea ding to changes in gene expression early in the stress response, are l argely unknown. It is clear, however, that gene expression associated with acclimatory responses is sensitive to the redox state of the cell . Of the many components which contribute to the redox balance of the cell, two factors have been shown to be crucial in mediating stress re sponses. Thiol/disulphide exchange reactions, particularly involving t he glutathione pool and the generation of the oxidant H2O2, are centra l components of signal transduction in both environmental and biotic s tresses. These molecules are multifunctional triggers, modulating meta bolism and gene expression. Both are able to cross biological membrane s and diffuse or be transported long distances from their sites of ori gin. Glutathione and H2O2 may act alone or in unison, in intracellular and systemic signalling systems, to achieve acclimation and tolerance to biotic and abiotic stresses.