Electron microscopy of susceptible and resistant near-isogenic (sr6/Sr6) lines of wheat infected by Puccinia graminis tritici. II. Expression of incompatibility in mesophyll and epidermal cells and the effect of temperature on host–parasite interactions in these cells

Abstract

Primary leaves of near-isogenic lines of Chinese Spring wheat, either with or without the temperature-sensitive resistance gene Sr6, were inoculated with an avirulent race of stem rust, maintained at 19, 26, or 28 °C, and harvested 1–4 days after inoculation. The infected tissues were examined with an electron microscope to determine the effects of these temperatures on the expression of the Sr6 gene. At 26 °C in the Sr6 line about one-half of the haustoria in mesophyll cells were disorganized or collapsed. None of the haustoria in epidermal cells showed any structural abnormality. In the susceptible (sr6) line, most haustoria were structurally normal at 26 °C whether they were in mesophyll or epidermal cells. There were no signs of disorganization or necrosis of infected host cells of either (Sr6 or sr6) line at 26 °C. At 28 °C in both lines, all haustoria in mesophyll cells were necrotic or collapsed, but those in epidermal cells were not. No host cell necrosis was observed in genotypically resistant leaves. At 19 °C, most haustoria and invaded mesophyll cells in the Sr6 line were necrotic. In the invaded epidermal cells neither haustoria nor host protoplasts were necrotic. In contrast, in a backcross line of Marquis wheat containing resistance gene Sr5 and infected with an avirulent race, both invaded mesophyll and epidermal cells were necrotic.