Plant Molecular Biology 4:275-283 (1985). 9 1985Martinus Nijhoff/Dr W. Junk Publishers, Dordreeht. Printedinthe Netherlands. Patterns of post-infectional protein synthesis in barley carrying different genes for resistance to the powdery mildew fungus J. M. Manners, A. D. Davidson & K. J. Scott Department of Biochemistry, University of Queensland, St. Lucia, 4067, Australia Keywords: 2-dimensional electrophoresis, resistance genes, Erysiphe graminis, Hordeum vulgare, protein synthesis Summary Pairs of susceptible and resistant, near-isogenic cultivars of Hordeum vulgare which differ for the Mla, Mlk and Mlp genes for resistance to Erysiphe graminis f. sp. hordei were inoculated with race 3 of this pathogen and patterns of protein synthesis associated with primary infection mapped using pulse-labelling with L-[35S]methionine and 2-dimensional electrophoresis. Extraction of proteins with buffer containing detergent revealed the enhanced synthesis of 5 and 8 polypeptides at 25 and 30 h respectively after inoculation of barley carrying the Mla gene (cvMla). The enhanced synthesis of these same polypeptides together with l I additional polypeptides was observed at 48 h and 72 h after inoculation of barley carrying either the Mlp (cvMlp) or Mlk (cvMlk) genes. The labelling of several major constitutive polypeptides was suppressed in cvMla at 24 h after inoculation; the labelling of six of these polypeptides was also suppressed in both cvMlp and cvMlk but not until 48 and 72 h after inoculation. These results indicate that changes occur in the synthesis of some common polypeptides following infection of cultivars carrying different resistance genes but the timing and extent of these changes varies with the resistance gene in the host. Introduction The obligate plant pathogen, Erysiphe graminis f. sp. hordei exhibits a high degree of host specifici- ty. A series of paired near-isogenic lines of barley have been developed (18) to provide cultivars con- taining one of several dominant genes specifying resistance to the powdery mildew fungus or the corresponding recessive alleles in a common genetic background. Using these near-isogenic cultivars it has been established that the fungal development as determined by individual resistance genes can differ considerably (6, 11, 17, 23). For example, the Algerian gene at the Mla locus conditions an early and highly effective resistance response with very little development of the pathogen occurring be- yond I day after inoculation (2, 13), whereas the Kwan (Mlk) and Psaknon (Mlp) genes condition a weaker response (11, 17, 23), and some develop- ment of the pathogen continues for several days. Biochemical events associated with the expression of resistance conditioned by these genes of barley has proved technically difficult to investigate. Recent improvements in procedures for 2-di- mensional electrophoresis of leaf proteins of cereals (8) have made it possible to investigate protein syn- thesis associated with the expression of resistance. Using these methods, the patterns of protein syn- thesis associated with the resistance of barley condi- tioned by the Mla, Mlp and Mlk genes are de- scribed. Materials and methods Plant and fungal material Near-isogenic cultivars of Hordeum vulgare which are either susceptible (S) or resistant (R) to race 3 of Erysiphe graminis f. sp. hordei were culti-