Anatomical features at the disarticulation zone in florets of fatuoid and nonfatuoid oat (Avena sativa L.)

Abstract

In oat (Avena sativa L.), the manner by which mature florets separate from the inflorescence depends on whether the plant is fatuoid or nonfatuoid and on whether it has naked or hulled grain. The anatomical basis for these differences is not well understood. Here, anatomical features were examined at the intersection of rachilla and lemma callus (disarticulation zone) in florets of fatuoid hulled-grain oat, which "shatter", and of nonfatuoid hulled-grain oat, fatuoid naked-grain oat, and nonfatuoid naked-grain oat, none of which shatter. A layer of one to several rows of small, thick-walled cells usually occurred at the disarticulation zone of fatuoid hulled-grain florets. This layer was less frequently observed at the disarticulation zone of nonfatuoid florets or fatuoid naked-grain florets. Visible at the early stages of development, these rows of small cells apparently form an abscission layer in mature florets of hulled-grain fatuoids. Disarticulation of florets is further assisted by the disintegration of medial parenchyma tissues of the lemma callus, resulting in the formation of lacunae around the vascular bundles. Although a layer of small cells in the disarticulation zone was often seen in mature fatuoid naked-grain florets, it did not function as an abscission layer.Key words: Avena, oat, fatuoid, disarticulation, abscission, shattering.