FURTHER STUDIES OF OSMOTIC AND PERMEABILITY RELATIONS IN PARASITISM

Abstract

Changes in host cell permeability induced by fungus parasites selected from several distinctive types of disease relationship were studied by plasmolytic methods.Puccinia graminis Tritici race 21 causes an increase in permeability to cells of the susceptible wheat varieties, Mindum and Little Club.Resistance of Mindum wheat to race 36 is associated with a local decrease of host cell permeability.Narcotization of Mindum wheat increases permeability and renders this variety more susceptible to race 36 of Puccinia graminis Tritici. This information, together with a hypothesis, already expounded, explaining mechanisms involved in food uptake by rusts, was used in the formulation of a theory illustrating a basic component of the factors responsible for rust resistance. This theory seems to interrelate the two main contrasting theories hitherto propounded.Permeability increase is also demonstrated as an effect of tissue invasion by Botrytis cinerea, Sclerotinia Sclerotiorum, and Phytophthora infestans on their respective susceptible hosts. This fact is allied with other information to explain the characteristic symptoms associated with the diseases caused by these fungi, and to propose an accessory role of permeability increase in the parasitism of these organisms.The probable cause of wilting induced by hadromycotic fungi is discussed, and the role of a permeability increase demonstrated for leaf cells of tomato subjected to the action of a filtrate of a culture of Fusarium Lycopersici is discussed in this connection.A decrease found in the permeability of tissues of swede "root" near the margin of a necrotic lesion caused by Phoma lingam was interpreted as being a change in accord with Brown's suggestion that a dry rot is determined by the ability of the host plant to restrict the amount of water reaching the parasite and so arrest the progress of its enzymic activity at some intermediate stage.