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.
