EARLY PHYSIOLOGICAL-RESPONSES ASSOCIATED WITH RACE-SPECIFIC RECOGNITION IN SOYBEAN LEAF TISSUE AND CELL-SUSPENSIONS TREATED WITH PSEUDOMONAS-SYRINGAE PV GLYCINEA

Pseudomonas syringae pv. glycinea race 4 (Psgr4) induces a compatible reaction on soybean cv. Mandarin leaves while race 6 (Psgr6) induces an incompatible hypersensitive response (HR). A single Psgr6 avirulence gene, avrA, when transformed into Psgr4, causes the resultant Psgr4(pAVRA) to induce a HR on Mandarin leaves. Mandarin leaf discs and suspension cells were inoculated and monitored for the K+ H+ and active oxygen responses, two early physiological events believed to be associated with recognition of HR-causing bacteria. Mandarin leaf discs exhibited a strong K+ H+ response following infiltration with either Psgr6 or Psgr4(pAVRA) but not Psgr4. Suspension cells derived from Mandarin hypocotyls reacted similarly when tested for the K+ H+ response to the Psg isolates. Luminol-dependent chemiluminescence (LDC) assays with suspension cells revealed active oxygen production concomitant with the K+ H+ response for both Psgr6- and Psgr4(pAVRA)-treated cells, but no such response was observed for Psgr4-treated cells. The data indicate that the K+ H+ and active oxygen responses are tightly correlated with recognition of the Psgr6 avrA gene or its products by Mandarin soybean leaves and suspension cells. © 1992.