ENVIRONMENTAL-STRESS SENSITIVITY OF AN ASCORBIC ACID-DEFICIENT ARABIDOPSIS MUTANT

L-ascorbic acid (vitamin C) is a powerful reducing agent found in mill imolar concentrations in plants, and is proposed to play an important role in scavenging free radicals in plants and animals. However, surpr isingly little is known about the role of this antioxidant in plant en vironmental stress adaptation or ascorbate biosynthesis. We report the isolation of soz1, a semi-dominant ozone-sensitive mutant that accumu lates only 30% of the normal ascorbate concentration. The results of g enetic approaches and feeding studies show that the ascorbate concentr ation affects foliar resistance to the oxidizing gas ozone. Consistent with the proposed role for ascorbate in reactive oxygen species detox ification, lipid peroxides are elevated in soz1, but not in wild type following ozone fumigation. We show that the soz1 mutant is hypersensi tive to both sulfur dioxide and ultraviolet B irradiation, thus implic ating ascorbate in defense against varied environmental stresses. In a ddition to defining the first ascorbate deficient mutant in plants, th ese results indicate that screening for ozone-sensitive mutants is a p owerful method for identifying physiologically important antioxidant m echanisms and signal transduction pathways. Analysis of soz1 should le ad to more information about the physiological roles and metabolism of ascorbate.