THE PROTECTIVE EFFECT OF RUST INFECTION AGAINST OZONE, SULFUR-DIOXIDEAND PARAQUAT TOXICITY SYMPTOMS IN BROAD BEAN

A localized but highly protective effect of rust infection towards inj ury induced by the air pollutants ozone and sulphur dioxide, either al one or in mixture and the herbicide paraquat was found. The effect was proportional to inoculum density, was non-translocatable, and depende nt on temperature. Protection continued even after the infection was n o longer active, and was induced by different strains of the fungus in cultivars of both broad bean and pea. Protection was not due to the e xclusion of pollutants resulting from stomatal closure. Histopathorogi cal investigations indicated that the effect was present in uncolonize d tissues adjacent to the site of infection. Ultrastructural studies s howed normal cell structure in the green islands surrounding the infec tion centres, even when nearby regions had collapsed. Peroxidase activ ity was increased rapidly in the infected tissues both in the colonize d and in the adjacent non-colonized cells. Such activity was not detec table at significant levels in non-parasitized tissues. The results ar e discussed in connection with the possible mechanisms involved.