THE DIFFERENTIAL-EFFECTS OF CELL-WALL-ASSOCIATED PHENOLICS, CELL-WALLS, AND CYTOSOLIC PHENOLICS OF HOST AND NONHOST ROOTS ON THE GROWTH OF 2 SPECIES OF AM-FUNGI

Experiments were conducted to test the hypothesis that cellular compou nds, especially wall-associated compounds, released during emergence o f secondary roots, stimulate the growth of arbuscular mycorrhizal (AM) fungi. Purified cell walls, crude cell-wall extracts, crude cytoplasm ic extracts, and phenolic compounds previously identified as cell wall -associated, from Ri T-DNA-transformed roots of host (Daucus carota L. ) and non-host (Beta vulgaris L.) were incorporated into growth medium and tested for their effects upon growth of the AM fungi Gigaspora gi gantea (Nicol. & Gerd.) Gerdemann and Trappe and Gigaspora margarita B ecker and Hall. Purified cell walls of both plants had little effect o n G. gigantea but non-host cell walls inhibited the growth of G. marga rita. Ferulic acid, a major constituent of non-host root, depressed th e growth of both fungi. Nothing tested which was unique to the non-hos t root affected hyphal growth to the point that contact would be prohi bited. Caffeic acid, found in D. carota cytoplasm, also depressed grow th of both fungi. Para-hydroxybenzoic acid, a constituent of D. carota roots, stimulated growth of G. margarita hyphae, but did not affect h yphal growth of G. gigantea. Vanillic acid, unique to D. carota root c ell-wall extracts, stimulated hyphal growth and branching of both fung i, and should increase the probability of contact between fungus and h ost root.