Inhibition of chitinolytic activities from tree species and associated fungi

Effects of two inhibitors, allosamidin and (2-acetamido-2-deoxy-D-glucopyranosylidene)amino phenylcarbamate (PUGNAC), have been assessed on chitinolytic activities of two plants, Pinus sylvestris L. and Eucalyptus pilularis Sm., and of seven fungi. Pinus sylvestris and E. pilularis root endochitinase activities were inhibited by allosamidin. Activities of P. sylvestris were more sensitive to inhibition than those of E. pilularis. The mechanism of inhibition varied with the plant species and the enzyme involved. PUGNAC inhibited beta-N-acetylglucosaminidase and exochitinase activities in root extracts from both plant species. In all cases PUGNAC acted as a reversible competitive inhibitor. Both inhibitors also affected chitinolytic activities from the fungi screened. Allosamidin inhibited endochitinase activities from both the mycorrhizal and pathogenic fungi tested. In addition, exochitinase activity from the ectomycorrhizal fungus Paxillus involutus (Batsch) Fr. was inhibited by allosamidin. PUGNAC inhibited beta-N-acetylglucosaminidase activity from all the fungi tested. PUGNAC was also a potent inhibitor of both exo- and endochitinase activities from the fungi, except P. involutus. Competitive inhibition was the most common form. These findings show allosamidin does inhibit endochitinase activity in plants and the ability of PUGNAC to inhibit not only beta-N-acetylglucosaminidase activity but also fungal endochitinase activity may be useful to distinguish between host and fungal endochitinase activities in symbiotic or pathogenic dual systems.