Lectins as Cytochemical Probes of the Developing Wheat Grain. Ii. Reaction of Wheat-Germ Lectin With the Nucellar Epidermis.

Abstract

Fluorescein-labelled wheat-germ lectin, which has a specific binding affinity for N-acetyl-D-glucosamine, has been shown to react specifically with nucellar epidermal cell walls in frozen and JB-4-embedded sections of developing wheat grain. The reaction was completely inhibited by preincubation of the lectin with diacetylchitobiose or triacetylchitotriose, two sugars known to be good inhibitors of the wheat-germ lectin combining sites. Labelled lectins with different specificities, and labelled non-lectin proteins such as bovine serum albumin, failed to react. Reaction with the nucellar epidermis increased to a maximum at approximately 14 days post anthesis (p.a.) and then progressively declined. At 35 days p.a., clear fluorescence was visible only in the inner crease area. Labelled wheat-germ lectin did not stain the nucellar projection at any stage of the developmental period studied. Treatment of wheat grain sections with chitinase almost completely abolished reactivity between nucellar epidermal cell walls and the lectin. Reactivity was slightly diminished following treatment with cellulase, but hemicellulase and two preparations of �-N-acetyl-D-glucosaminidase had no effect. These observations indicate the probable presence of a chitin-like structure in nucellar epidermal cell walls, which may be an endogenous saccharide receptor for wheat-germ lectin in developing or germinating wheat grains.