Changes in the subcellular distribution of glutathione during virus infection in Cucurbita pepo (L.)

Changes in the subcellular distribution and quantification of glutathione were studied with electron microscopic immunogold cytochemistry in Zucchini yellow mosaic virus (ZYMV)-infected Styrian pumpkin plants (Cucurbita pepo L. ssp. pepo var. styriaca Greb.) two weeks after inoculation. The amount of gold particles bound to glutathione was statistically evaluated for different cell structures, including mitochondria, plastids, nuclei, peroxisomes, and cytosol. In general, ZYMV-infected plants showed higher gold labelling density in intact mesophyll cells of the 5th (older leaves) and the youngest fully developed leaves (younger leaves), and decreased levels of glutathione within root tip cells when compared to the control. In general, within older and younger leaves the highest amount of gold particles was found in mitochondria and the lowest amount in plastids. In ZYMV-infected older leaves, an increase in glutathione was found in peroxisomes (1.7-fold), the cytosol (1.6-fold), mitochondria (1.4-fold), and nuclei (1.2-fold), whereas glutathione levels in plastids did not differ significantly when compared to control cells. In ZYMV-infected younger leaves elevated glutathione contents were found in the cytosol (3-fold), nuclei (2.1-fold), peroxisomes (1.8-fold), and plastids (1.5-fold), whereas mitochondria showed an insignificant decrease in glutathione levels in comparison to the control. In root tip cells of ZYMV-infected plants the amount of gold particles bound to glutathione was decreased in all investigated cell structures by between 0.7- to 0.8-fold. Additionally, total glutathione contents were determined in older and younger leaves using high-performance liquid chromatography (HPLC), which revealed no significant differences between control and ZYMV-infected leaves. The relevance of the results of both methods were compared and are discussed.