Summary auto-generated
This study compared the antifungal properties of chitinases from plant grains (wheat, barley, maize) with those from three bacterial species (Serratia marcescens, Streptomyces griseus, Pseudomonas stutzeri). Chitinases were tested for their ability to inhibit hyphal growth of two fungi: Trichoderma reesei and Phycomyces blakesleeanus. Plant chitinases showed potent antifungal activity at concentrations as low as 1 microgram, whereas bacterial chitinases had no effect even at 50 micrograms. This difference correlated with distinct enzymatic mechanisms: plant chitinases functioned as endochitinases (cleaving chitin internally) and possessed lysozyme activity, while bacterial chitinases were exochitinases (cleaving from chitin chain ends) lacking lysozyme activity. The researchers also identified p-nitrophenyl-β-D-N,N'-diacetylchitobiose as a novel chromogenic substrate for bacterial exochitinases but not plant endochitinases. These findings support the hypothesis that plant chitinases evolved to defend against fungal pathogens, and suggest that genetic engineering approaches to enhance plant disease resistance should use plant chitinase genes rather than bacterial ones.
Key findings
- Plant grain chitinases inhibited fungal hyphal growth at 1 microgram or less, while bacterial chitinases showed no antifungal activity even at 50 micrograms.
- Plant chitinases function as endochitinases with associated lysozyme activity, whereas bacterial chitinases are exochitinases lacking lysozyme activity.
- The difference in antifungal activity correlates with substrate specificity and mechanism of action rather than overall chitin-degrading capacity.
- p-Nitrophenyl-β-D-N,N'-diacetylchitobiose serves as an excellent chromogenic substrate for bacterial exochitinases but is resistant to plant endochitinases.
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
SUMMARY: Chitinases were isolated from the grains of wheat, barley and maize, and compared with those obtained from Serratia marcescens, Streptomyces griseus and Pseudomonas stutzeri for antifungal activity and enzyme specificity. The six enzymes were tested for antifungal activity using an assay based upon inhibition of hyphal extension of the fungi Trichoderma reesei and Phycomyces blakesleeanus. Antifungal activity was observed with as little as 1 μg of each of the grain chitinases, whereas none of the bacterial chitinases had any effect on hyphal extension, even at 50 μg chitinase per assay. This difference in antifungal activity correlated with the different mechanisms of action of the two classes of enzymes. In common with other plant chitinases, the grain chitinases functioned as endochitinases and contained lysozyme activity. In contrast, the bacterial enzymes were exochitinases and hydrolysed the chromogenic trisaccharide analogue p-nitrophenyl-β-D-N, N'-diacetylchitobiose, which proved to be an excellent substrate for assaying bacterial chitinases. These experiments strengthen the hypothesis that plant chitinases function to protect the host against fungal infections.