PHOTOSYNTHETIC ELECTRON-TRANSPORT IS DIFFERENTIALLY AFFECTED DURING EARLY STAGES OF CULTIVAR/RACE-SPECIFIC INTERACTIONS BETWEEN POTATO AND PHYTOPHTHORA-INFESTANS

The influence of the early stages of fungal infection on chloroplast metabolism was studied in cultivar/ race-specific interactions between potato (Solanum tuberosum L. cv. Datura) and the late-blight fungus Phytophthora infestans. The accumulation of several mRNAs encoding components of the photosynthetic apparatus was not affected, either in compatible or in incompatible interactions, However, within 3 h after inoculation of potato leaves with fungal spores, a change in the photochemistry of photosystem II was detectable by measuring chlorophyll a fluorescence. Characteristic fluorescence parameters, such as maximum fluorescence yield (F-m), variable fluorescence yield (F-v) and photochemical efficiency (F-v/F-m), were specifically reduced in the compatible host/pathogen interaction. Analyses of photochemical and nonphotochemical fluorescence quenching showed an increase in the photochemical fraction. The amounts of two selected thylakoid membrane proteins and of total chlorophyll remained unchanged during this process, suggesting that the functional modification of the electron-transport system was not correlated with a change in the composition of the photosynthetic apparatus. The alterations of photosynthetic electron transport represent a rapidly detectable and sensitive physiological marker for compatible interactions in the potato/Phytophthora infestans pathosystem.