Differential absorption and localization of two Sclerotinia sclerotiorum endo-polygalacturonases in soybean hypocotyls

Abstract

The isolate B-24 of the necrotrophic fungus Sclerotinia sclerotiorum produces two major endo-polygalacturonases (PG-II and PG-IV) during infection of soybean seedlings. By a combination of biochemical, immunofluorescence and morphological techniques it was shown that they were differentially absorbed by soybean hypocotyl tissue, becoming located preferentially at different sites. PG-IV was absorbed much more than PG-II and it was able to permeate the unwounded surface of the hypocotyl and accumulate in the cortical cell layer where it produced an increase of autofluorescence and a marked loss of adhesion of cortical cells. When applied to the cut-end surface of the hypocotyl PG-IV remained localized near the site of the treatment. In contrast PG-II was not absorbed through the epidermis but, when applied to the cut surface of hypocotyl it was transported some distance into the tissue possibly via the vascular bundles, The different behaviour of the two PGs together with their different properties suggest they play a different but complementary role in the pathogenic strategy of S. sclerotiorum.