Metabolic Regulation in Diseased Leaves. I. The Respiratory Rise in Barley Leaves Infected with Powdery Mildew

Abstract

Photosynthetic and respiratory activities were measured in leaves of Hordeum vulgare var. Manchuria after infection with Erysiphe graminis var. hordei. Two isogenic lines, one resistant to infection and the other highly susceptible, were examined. Photosynthesis and chlorophyll content of resistant leaves was unaffected by infection. Respiration increased slightly and small increases were observed in the activities of enzymes of glycolysis, the pentose-P-pathway, and the tricarboxylic acid cycle. Infection of susceptible leaves resulted in a slight increase in photosynthesis 48 hours after inoculation, but subsequently photosynthesis rapidly declined in these leaves. Decreases were also noted in the Hill reaction, photoreduction of NADP+. NADPH-diaphorase, and aldolase. Respiration increased in infected leaves, reaching a maximum rate about 144 hours after inoculation. The activities of glucose-6-P dehydrogenase and 6-P-gluconate dehydrogenase showed changes similar to that observed for respiration. Respiration and the activities of these 2 enzymes did not change after infection of leaves lacking chloroplasts. It is suggested that the pathogen is not directly responsible for the increase in respiration in green leaves, but that this is a response of the host cells to a loss of photosynthetic capacity.