THE PHYSIOLOGY OF HOST–PARASITE RELATIONS: II. THE EFFECT OF PUCCINIA GRAMINIS TRITICI ERIKS. AND HENN. ON THE RESPIRATION OF THE FIRST LEAF OF RESISTANT AND SUSCEPTIBLE SPECIES OF WHEAT

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Abstract
The first leaves of resistant (var. Khapli) and susceptible (var. Little Club) species of wheat were heavily inoculated with P. graminis (Race 15B). The effect of the frequency of the pustules on their size and on the leaves is described. The oxygen consumption, total dry weight, total nitrogen, and sugar contents of leaf disks were measured at frequent intervals after inoculation. At infections of Little Club massive increases in dry weight occurred in 10 to 15 days, but the percentage total nitrogen remained close to that of healthy leaves. Oxygen consumption per unit dry weight or per unit of tissue nitrogen rose to from 2.5 to 3.0 times that for healthy tissue and then fell off again. The duration and degree of the rise were dependent on environmental conditions. At infections on Khapli, both dry weight and the percentage total nitrogen declined rapidly and the leaves turned yellow and died in about eight days, suggesting a rapid breakdown of protein. Oxygen consumption per unit dry weight or per unit of tissue nitrogen rose more rapidly, to from 2.0 to 2.5 times that of healthy tissue, and declined again sooner than at infections on Little Club. With both species, the 'accumulation' at infections of radioactive glucose, or its products, roughly paralleled the course of respiration. With leaves of Little Club, initially low in carbohydrate and having a low respiratory quotient, a marked rise in the respiratory quotient occurred at developing infections; little or no rise occurred with Khapli. The results of the sugar analyses suggested that the increase in respiration following infection was not initially dependent on an increase in the sugar content above that found in the healthy leaf. The significance of the results is discussed.

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