Induced accessibility and inaccessibility to ¤Blumeria graminis¤ f.sp. ¤hordei¤ in barley epidermal cells attacked by a compatible isolate

First leaves of the barley line Riso-5678S were subjected to a double inoculation procedure ('inducer' followed by 'challenger') with conidia of a genetically compatible isolate of Blumeria graminis (DC.) Speer (Syn. Erysiphe graminis DC.). In control leaves, attacked by appressoria from a single inoculation, approximately 67% of penetration attempts successfully formed haustoria.

However, in epidermal cells successfully penetrated by the inducer, almost all attacks by the challenger succeeded (> 90%). Thus, accessibility was induced in these cells. In some cases, accessibility was also induced in immediately adjacent cells, but not in more distant cells. In contrast, where inducer attack failed, almost all attacks by the challenger failed (< 5% succeeded).

Thus, inaccessibility was induced in these cells. Inaccessibility was also induced in immediately adjacent cells, but not in more distant cells. The size of papillae formed in challenged cells could not account for induced inaccessibility. However, induced accessibility appeared to be associated with suppression of localized autofluorescent host cell responses to challenger attack, whereas inaccessibility was associated with increased frequency and intensity of such responses.

This implies that induced changes may relate to modification in cells' ability to synthesize phenolic compounds as a defensive response. (C) 1999 Academic Press.