An anti-petunia glycine-rich protein 1 (ptGRP1) antibody was used for biotin-streptavidin-alkaline phosphatase localization of this protein. In petunia stem and leaves grown under different light conditions, these studies revealed a complex pattern of cell localization for this protein. Levels of ptGRP1 were shown to decrease with developmental age of the tissue, appearing to correlate directly with expansive growth and inversely with lignification. Significantly, plants grown under low light (approximately 32 mumol m-2 sec-1 at noon) showed at least an eightfold increased level of ptGRP1 protein throughout ptGRP1's expression period when compared to plants grown under higher light (approximately 80 mumol m-2 sec-1 at noon). Evidence also indicated that for one cell type in which ptGRP1 is localized, this protein is imported rather than synthesized. In addition, confocal microscopy studies suggested that ptGRP1 is deposited at the cell wall/membrane interface rather than within the cell wall.