The Role of Wheat Awns in the Seed Dispersal Unit

TLDR

Wild wheat seed dispersal units feature two prominent awns that help balance the unit during descent. Cellulose fibrils bend the awns in response to humidity changes, while silicified hairs guide propulsion so the unit moves only toward the seeds. The awns act as a humidity‑driven motor, propelling seeds into the ground and enabling seed dispersal.

Abstract

The dispersal unit of wild wheat bears two pronounced awns that balance the unit as it falls. We discovered that the awns are also able to propel the seeds on and into the ground. The arrangement of cellulose fibrils causes bending of the awns with changes in humidity. Silicified hairs that cover the awns allow propulsion of the unit only in the direction of the seeds. This suggests that the dead tissue is analogous to a motor. Fueled by the daily humidity cycle, the awns induce the motility required for seed dispersal.