K-252a inhibits the response of tomato cells to fungal elicitors in vivo and their microsomal protein kinase in vitro

Two characteristic responses of plant cells to fungal elicitors, induction of phenylalanine ammonia-lyase activity and of ethylene biosynthesis, were studied in suspension-cultured tomato cells. Induction of both responses was completely blocked by 500 nM K-252a, a known inhibitor of mammalian protein kinases. About 100 nM K-252a caused half-maximal inhibition. In vitro, K-252a inhibited protein kinase activity in microsomal preparations from tomato cells. Inhibition was competitive with respect to ATP and had a K 1 of about 15 nM. Thus, protein kinases sensitive to K-252a occur in plants and might be important for the plant's response to fungal elicitors.