Abstract The role of cysteine proteinases in the growth and development of healthy and PVY NTN infected potato plants ( Solanum tuberosum L. cv. ‘Desiree’) and the subcellular localization of a particular potato leaf cysteine proteinase PLCP-2 were studied in tissue culture. The immunolocalization of PLCP-2 on the ultrathin sections of potato plants was examined by electron microscopy. PLCP-2 was found in protein bodies in vacuoles, in cytoplasm and in cell walls of shoot tips, leaves, stems and root tips. PLCP-2 was observed at all locations where its endogenous inhibitors PCPI 6·6 and multicystatin were localized, which indicates the possible regulation of PLCP-2 by these inhibitors in vivo . In order to study the physiological role of cysteine proteinases in potato plants, their total activity was diminished by introducing Ep-475 into the growth media and further into the plant through root absorption. The morphological characteristics of healthy and PVY NTN infected plants grown on media with added Ep-475 were followed. The results suggest that cysteine proteinases are involved in the synthesis and transport of plant metabolites and in processes that lead to organogenesis. Observations also indicate that the ratio between cysteine proteinases and their endogenous inhibitors in potato plants is altered after infection with PVY NTN .