Effects of zucchini yellow mosaic virus infection on the subcellular distribution of glutathione and its precursors in a highly tolerantCucurbita pepocultivar

Abstract

Glutathione (γ-glutamyl-cysteinyl-glycine) is an antioxidant that plays important protective roles during pathogen attack. Glutathione synthesis is a highly compartment-specific pathway and relies on the supply of its precursors cysteine, glutamate, and glycine. To study the importance of glutathione in the development of tolerance and resistance, glutathione and its precursors were quantified with cytohistochemical methods in a highly tolerant cultivar (‘Quine’) of Cucurbita pepo L. during zucchini yellow mosaic virus (ZYMV) infection. Glutathione concentrations were strongly increased in almost all cell compartments of younger leaves (up to 247% in peroxisomes), older leaves (up to 73% in the cytosol), and roots (up to 104% in nuclei) during ZYMV infection. In addition, glutathione precursor concentrations were generally unchanged or increased in all cell compartments of younger leaves and roots, indicating that glutathione synthesis in these organs was not limited by low levels of glutathione precursors. The lower increase of glutathione in older leaves could be caused by strongly decreased levels of glycine in plastids (42%) and the cytosol (53%) during ZYMV infection, as they are the main centers for glutathione synthesis. Nevertheless, as the increase in glutathione was in general much higher than that observed in a highly susceptible cultivar in previous studies, we can conclude that elevated glutathione concentrations can be strongly correlated with the development of tolerance during ZYMV infection.