Cereal Chem 62:35-40   |  VIEW ARTICLE
A Microscopic Study on the Development of a Layer in Barley That Causes Hull-Caryopsis Adherence.

R. L. Gaines, D. B. Bechtel and Y. Pomeranz. Copyright 1985 by the American Association of Cereal Chemists, Inc. 

The cementing layer in barley that causes the hull to adhere to the caryopsis was investigated using transmission electron microscopy and cytochemistry. The cementing substance appeared on the surface of the pericarp two days after flowering prior to the physical contact between the caryopsis and the hull. The cementing layer increased in thickness throughout kernel development. The substance is secreted solely by the pericarp epidermis, as no cementing material is found associated with the hull until after pericarp-hull contact. Cytochemical tests for protein and carbohydrate gave negative results for the cementing layer. Thickness of the cementing layer in mature kernels is highly variable, ranging from 130 to over 600 nm. The cement has a distinct morphology, being nearly electronlucent and bearing faint lamellar striations. The junction between the hull and cement is smooth and distinct, whereas the junction between the cement and pericarp is very irregular. Mechanical separation of the hull from the caryopsis usually results in the cementing layer remaining attached to the pericarp.