Observations on the Scutellum. II. Histochemistry and Autofluorescence of the Cell Wall in Mature Grain and During Germination of Wheat, Barley, Oats and Ryegrass

Abstract

Histochemical studies and fluorescence microscopy of the scutella of wheat, barley, oats and ryegrass indicate that the cell walls of these grasses are basically similar in composition. They are all periodic acid-Schiff's positive, presumably owing to large amounts of hemicelluloses such as xylans. All scutellar cell walls stain with protein stains at all stages of germination, with the exception of the epithelial cell walls of oats which do not stain. Scutellar cell walls stain metachromatically red to purple (hydrated sections) or green (dehydrated sections) when stained with toluidine blue 0. The red to purple colour is indicative of free carboxyl groups, usually owing to the presence of pectin. However, this is not confirmed in this case since two pectin stains fail to react. The green coloration with toluidine blue staining is indicative of phenolic compounds (lignin). This conclusion is supported by the autofluorescence shown by the scutella of all genera. The autofluorescence of oats and rye- grass is initially low, especially at the apex, but increases as germination progresses. Wheat and barley lose fluorescence intensity 3 days after germination but later regain it.