CHOLINE-INDUCED AND ACETYLCHOLINE-INDUCED CHANGES IN THE MORPHOLOGY OF FUSARIUM-GRAMINEARUM - EVIDENCE FOR THE INVOLVEMENT OF THE CHOLINE TRANSPORT-SYSTEM AND ACETYLCHOLINESTERASE

The response of Fusarium graminearum to choline, acetylcholine and a n umber of related analogues was investigated and their ability to induc e a morphological response quantified. A number of mutants resistant t o the alkylating agent nitrogen mustard (nim strains) were generated a nd found to have lost the ability to transport choline. These mutants were found to be insensitive to choline and acetylcholine but not to b etaine, ethanolamine and other analogues. In addition, the non-competi tive inhibitor hemicholinium-3 was also found to reduce the morphologi cal effect of choline, proving that transport of choline into the hyph a is essential for the morphological response. Acetylcholinesterase in hibitors blocked the morphological response to acetylcholine but had n o effect on the response to choline, suggesting the presence of a memb rane- or wall-bound acetylcholinesterase that hydrolyses acetylcholine to choline which subsequently induces the morphological response. Stu dies on the in vivo chitin synthase activity revealed that addition of choline caused a transient 75% increase in chitin synthase activity w ithin 30 s, the rate rapidly returning to that observed before the add ition of choline. No such effect was observed with the nim mutants.