Levels of elicitor-active β(1–4) linked N-acetyl-d-glucosamine oligosaccharides in the lignifying tissues of wheat**

The physiological significance of elicitor-active chitin oligosaccharides is generally unknown, both in terms of whether they are involved in the plant response to the polymer or whether they have any significance in fungal infections. In the experiments reported here we have investigated the significance of elicitor-active chitin oligosaccharides N -acetyl- d -glucosamine (GlcNAc) 4–6 in the induction of defensive lignification in wounded wheat leaves. Our aim was to determine whether these elicitor-active oligosaccharides could be detected in planta following treatment with chitin, and whether the levels detected could account for the lignification induced by chitin. The levels of chitin oligosaccharides (GlcNAc) 4 in wounded wheat leaves treated with chitin or the chitin tetramer (GlcNAc) 4 have been monitored by HPLC analysis of tissue extracts. Oligomer profiles from chitin-treated leaves show that the polymer is hydrolysed to produce monomer and oligosaccharides up to at least the hexamer, presumably due to the action of endochitinases and other hydrolytic enzymes. The tetramer (GlcNAc) 4 is also hydrolysed when applied to leaves, with the non-eliciting dimer and monomer being the major products. When concentrations of (GlcNAc) 4 sufficient to elicit lignification are administered, tissue levels of (GlcNAc) 4 observed over 12 h are considerably higher than the combined level of elicitor-active oligosaccharides (GlcNAc) 4–6 observed in leaves treated with chitin at an eliciting dose. Significantly, when the (GlcNAc) 4 is administered at a lower, non-eliciting, concentration which does not induce lignification, the measured level of (GlcNAc) 4 is still much greater than the level of elicitor-active oligosaccharides (GlcNAc) 4–6 observed in leaves treated with a concentration of chitin that does induce lignification. The experimental evidence therefore fails to support the hypothesis that the previously identified elicitor-active oligosaccharides (GlcNAc) 4–6 are solely responsible for elicitation of lignification by chitin, and hence casts doubt on their importance as key signals in triggering defensive lignification in wheat.