Responses of barley cells to puncture by microneedles and to attempted penetration by Erysiphe graminis f.sp. hordei

Abstract

Responses to puncture by microneedles were compared with responses to attempted penetration by Erysiphe graminis f.sp. hordei in epidermal cells of coleoptiles of Hordeum vulgare. Wounds left by needles were repaired within a few minutes so that cells could withstand development of turgor, although no plug was visible at the wound site and cytoplasmic aggregation at the site was not necessary for repair. These initial (stage I) repairs were more effective in the cutinized than in the non-cutinized cell surface. Stage I was followed by a second set of repairs (stage II) in which cytoplasm aggregated at the wound site where a visible wall apposition (wound plug) was deposited. Similar appositions were deposited as encasements on the surfaces of needles left in cells or as papillae at sites of attempted penetration by E. graminis. Cytoplasm aggregated in cells adjacent to cells under fungal attack but not in cells adjacent to cells with needle punctures. Furthermore, histochemical tests indicated that needle-induced wound plugs and encasements contained cellulose and pectin, whereas fungal-induced papillae did not; and papillae contained phenols and basic staining material, whereas wound plugs and encasements did not. The differences between the stage II wound response and fungal-induced response suggest that fungal attack generates inducing factors not produced by mechanical penetration.