An Arabidopsis Mutant Depleted in Glutathione Shows Unaltered Responses to Fungal and Bacterial Pathogens. Mike J. May. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, 0X1 3RB, UK. Jane E. Parker (2), Michael J. Daniels (2), Christopher J. Leaver (1), and Christopher S. Cobbett (3). (1) Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, 0X1 3RB, UK; (2) The Sainsbury Laboratory, Norwich Research Park, Colney, Norwich, NR4 7UH, UK; (3) Department of Genetics, The University of Melbourne, Parkville, Australia, 3052. MPMI 9:349-356. Accepted 1 March 1996. Copyright 1996 The American Phytopathological Society.

We have previously shown that the leaf glutathione (GSH; (-glutamylcysteinyl glycine) content of a cadmium-sensitive mutant of Arabidopsis thaliana, cad2-l, was decreased to 30% of that in the wild-type parental accession Columbia (Col-0) (R. Howden et al., Plant Physiol. 107:1067-1073, 1995). Here we show that GSH deficiency in this mutant does not alter responses to fungal and bacterial pathogens. The timing and extent of asexual (sporangiophore) and sexual spore (oospore) development of a virulent strain of Peronospora parasitica, Noco2, in cad2-l were identical to those in Col-0. The resistance of cad2-l to a strain of P. parasitica, Welal, which is avirulent in Col-0, was not altered. Furthermore, attempted infection by Welal was associated with a 2.5-fold increase in the level of glutathione in cad2-l and a 1.3-fold increase in Col-0, and in accumulation of PRl mRNA in both mutant and wild-type plants. However, while in Col-0 levels of glutathione dropped to the initial levels 3 days after inoculation, the increase was maintained in the mutant, cad2-l. A virulent strain of Pseudomonas syringae pv. tomato (DC3000) grew at the same rate and to the same titer in both cad2-l and Col-0 and both plant lines were equally resistant to the same strain carrying the avirulence gene avrB from the soybean pathogen P. syringae pv. glycinea. Both cad2-l and Col-0 acquired resistance to Noco2 and P. syringae pv. tomato (DC3000) after treatment with 5 (M or 10 (M 2,6-dichloroisonicotinic acid (INA) and this was associated with accumulation of PRl mRNA. A 1.6-fold increase in the level of glutathione in Col-0 and a 2.3-fold increase in cad2-l were also observed and were maintained in both lines during the course of the experiment. These results demonstrate that the depletion of glutathione levels by 70% in Arabidopsis does not alter its responses to the pathogens analyzed. The impact of these results on the proposed functions of GSH and the way in which active oxygen species are generated and reduced in plant-pathogen interactions is discussed.