Resistance responses of potato to vesicular-arbuscular mycorrhizal fungi under varying abiotic phosphorus levels

• Published in: Plant physiology (Bethesda) 1992-09, Vol.100 (1), p.341-351
• Main Authors: McArthur, D.A.J, Knowles, N.R
• Format: Article
• Language: English
• Subjects: ACTIVIDAD ENZIMATICA; ACTIVITE ENZYMATIQUE; Agronomy. Soil science and plant productions; ANTIMETABOLITE; ANTIMETABOLITOS; Biological and medical sciences; Cell walls; COMPOSE PHENOLIQUE; COMPUESTOS FENOLICOS; DISPONIBILIDAD DE NUTRIENTES; DISPONIBILITE D'ELEMENT NUTRITIF; ETHYLENE; Ethylene production; ETILENO; FOSFORO; Fundamental and applied biological sciences. Psychology; Fungi; GLOMUS; Glomus fasciculatum; Hyphae; Infections; Inoculum; Metabolism; Microbe-Plant Interactions; OXIDORREDUCTASAS; OXYDOREDUCTASE; Parasitism and symbiosis; PEROXIDASAS; PEROXYDASE; PHOSPHORE; Plant interaction; Plant physiology and development; Plant roots; Plants; RACINE; RAICES; SOLANUM TUBEROSUM; SUBSTANCE DE CROISSANCE VEGETALE; SUSTANCIAS DE CRECIMIENTO VEGETAL; Symbiosis
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.100.1.341

In mycorrhizal symbioses, susceptibility of a host plant to infection by fungi is influenced by environmental factors, especially the availability of soil phosphorus. This study describes morphological and biochemical details of interactions between a vesicular-arbuscular mycorrhizal (VAM) fungus and potato (Solanum tuberosum L. cv Russet Burbank) plants, with a particular focus on the physiological basis for P-induced resistance of roots to infection. Root infection by the VAM fungus Glomus fasciculatum ([Thaxt. sensu Gerdemann] Gerdemann and Trappe) was extensive for plants grown with low abiotic P supply, and plant biomass accumulation was enhanced by the symbiosis. The capacity of excised roots from P-deficient plants to produce ethylene in the presence or absence of exogenous 1-amino cyclopropane-1-carboxylic acid (ACC) was markedly reduced by VAM infection. This apparent inhibition of ACC oxidase (ACCox) activity was localized to areas containing infected roots, as demonstrated in split-root studies. Furthermore, leachate from VAM roots contained a potent water-soluble inhibitor of ethylene generation from exogenous ACC by nonmycorrhizal (NM) roots. The leachate from VAM-infected roots had a higher concentration of phenolics, relative to that from NM roots. Moreover, the rates of ethylene formation and phenolic concentration in leachates from VAM roots were inversely correlated, suggesting that this inhibitor may be of a phenolic nature. The specific activity of extracellular peroxidase recovered in root leachates was not stimulated by VAM infection, although activity on a fresh weight basis was significantly enhanced, reflecting the fact that VAM roots had higher protein content than NM roots. Polyphenol oxidase activity of roots did not differ between NM and VAM roots. These results characterize the low resistance response of P-deficient plants to VAM infection. When plants were grown with higher abiotic P supply, the relative benefit of the VAM symbiosis to