Effect of intensity and quality of light on peroxidase activity associated with Septoria leaf spot of tomato

Abstract

Extracts of tomato (Lyeopersicon esculentum Mill. cultivar Heinz 1350) leaves infected by Septoria lycopersici Speg. were examined for peroxidase activity throughout the period of infection and disease development. These experiments were made to determine whether peroxidase activity was influenced by light, and, if so, the degree of effect of various wavelengths and intensities, other environmental conditions being constant. Consequently, paper electrophoresis scans of peroxidase isozymes showed a bimodal pattern of a conspicuous increase in staining intensity reflecting a high level of enzymatic activity of major components in leaves 4 days after their inoculation with the fungus. At 6 days minimal values were obtained, whereas somewhat enhanced isozyme activity occurred at later stages in the progression of the disease and the maturation of pycnidia and pycnospores. As well, decreased light intensity increased both the severity of the disease and the peroxidase activity in the infected leaf. This effect of light intensity was most evident 10 days after inoculation. Furthermore, treatment with various wavelengths of light produced the most marked effects on enzyme activity in the later rather than in the earlier stages of disease development. Maximal peroxidase activity occurred 10 days after inoculation, with a major peak in green light and a second peak in red light. These results indicate that the light regime is an important factor to consider in evaluating not only symptom expression but also analyses of the enzyme activity in this leaf spot disease.