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Metabolic Regulation in Diseased Leaves II. Changes in Nicotinamide Nucleotide Coenzymes in Barley Leaves Infected With Powdery Mildew ¹

Biochemistry Department, University of Sydney, Sydney, Australia

Nicotinamide nucleotide coenzymes were estimated spectrophotometrically in noninfected barley leaves and leaves infected with Erysiphe graminis var hordei (powdery mildew). Amounts of NADH, NADP⁺ and NADPH were not altered by infection. In contrast, the NAD⁺ content rose sharply and at 144 hours was 100% greater than in noninfected leaves. The respiratory rate was increased in infected leaves and the pattern of this increase was similar to that of NAD⁺.

The effect of infection on the intracellular distribution of NADP⁺ was examined by fractionating lyophilized leaves in a nonaqueous medium. In noninfected leaves almost all of the NADP⁺ was localized in the chloroplasts. In infected leaves where some chloroplast breakdown occurs, about 60% of the NADP⁺ was detected in the nonchloroplast part of the cell. This intracellular redistribution of NADP⁺ is discussed in relation to the increased pentose-P pathway activity occuring after infection.