Fine structural and biochemical studies on the infection of vicia faba l. by uromyces and botrytis

Abstract

(1) Fine structural and biochemical studies have been made on the infection of Vicia faba L. by Uromyces fabae (obligate parasite) and Botrytis fabae (facultative parasite). (2) Fine structural observations of host cells infected with U. fabae showed that they could be divided into two categories, (a) cells with increased capacity for synthesis (2-8 days after infection), which are characterised by an increase in the volume of the cytoplasm and by an increase in the size of cytoplasmic organelles (i.e. rough endoplasmic reticulum (ER), nucleus, mitochondria); (b) cells with decreased metabolic activities (12-20 days after infection) and characterised by senescence of the cytoplasm and by the reduction in the size of cytoplasmic organelles, especially chloroplasts. Numerous vesicles were found to be associated with the inner membrane of chloroplasts in such infected cells. (3) Electron microscopic observations showed that cells from leaves infected with B. fabae, can also be divided into two categories, (a) cells in the centre of the necrotic lesion which are characterised by blackening and the destruction of the tissues;(b) cells at the periphery of the necrotic lesion, which are characterised by an increase in the volume of the cytoplasm, an increase in the size of cytoplasmic organelles, by the presence of lomasomes, and by the presence of vesicular inclusions in the cytoplasm and electron dense bodies in the extracellular spaces.(4) The fine structure of U. fabae resembles that of other comparable obligate parasites, except for the presence of an electron dense ring in the middle part of the haustorial neck, and vesicular and tubular structures in the vacuoles of this fungus. The growth of B. fabae on the host tissues was found to be relatively limited as compared with its growth on artificial medium. Likewise, the cytoplasm and cytoplasmic organelles of B. fabae were found to be denser when the fungus was grown on artificial media. Lomasomes were found to be common in the cytoplasm of this fungus, and the relation of this structure to the hydrolysis of the host cell wall is discussed. (5) Several biochemical tests were made to assess the significance of some of the structural changes taking place in the host as a result of infection (i.e. amino acid composition, protein synthesis and photochemical activities of isolated chloroplasts). Special emphasis was placed on the effect of both infections on the latter process. The results can be summarised as follows:- (a) infection with U. fabae caused an increase in the rate of the Hill reaction, cyclic phosphorylation (2-10 days after infection), followed by a decrease in such activity (12-20 days after infection). The infection also caused an alteration to ATP:e(^-) ratio. .(b) infection with B. fabae caused a marked reduction in all photochemical activities tested, (i.e. Hill reaction, cyclic and uncyclic phosphorylation).(c) The observed effects were found to be independent of the chlorophyll concentration and the reduction in the photosynthetic area.