EFFECT OF FUNGAL TOXINS ON INDUCTION OF PHENYLALANINE AMMONIA-LYASE ACTIVITY IN ELICITED CULTURES OF HYBRID POPLAR

Eleven fungal phytotoxins were tested for their ability to selectively interfere with elicitor-induced increases in phenylalanine ammonia-ly ase (PAL) activity in hybrid poplar suspension cultures. The toxins va ried greatly in their impact on cell growth, oxygen consumption and PA L induction. At a concentration of 10(-4) M, cytochalasin A and zearal enone severely depressed values for all three parameters, while fusari c acid, cytochalasin B, fumonisin B, and fusarenone X were somewhat le ss inhibitory. Fumonisin B, displayed selectivity in that it strongly inhibited growth and respiration, while having no effect on PAL induct ion. By contrast, pinolidoxin and putaminoxin were also selective, sin ce at 10(-4) M they had little effect on cell growth but were able to suppress PAL induction by 40-50%. Selective suppression of PAL inducti on was also revealed when lower concentrations of fusarenone X were as sayed. These results suggest that, in addition to their cytotoxic effe cts, some phytotoxins could directly suppress specific defence respons es in plant cells during pathogenesis. (C) 1997 Elsevier Science Irela nd Ltd.