Evaluation of the emerging coleorhiza and radicle of Bromus tectorum using SEM and light microscopy

Abstract

The coleorhiza is a nonvascular sheath that encloses the embryonic radicle in Gramineae, and is generally the first tissue to emerge during germination. Coleorhiza cells develop extensions similar to root hairs, which are difficult to study quantitatively in situ because they are extremely sensitive to desiccation and breakage. Protective, absorptive and adhesive roles have been postulated for this tissue, but have received limited attention, This study used scanning electron microscopy (SEM) and light microscopy (LM) to characterize the coleorhiza and radicle during germination of Bromus tectorum, a species that often emerges from the soil surface in semiarid habitats.Caryopses (seeds) were imbibed at various water potentials over solutions of polyethylene glycol (PEG) or in soil until coleorhizae had emerged. For SEM, seeds imbibed over PEG were frozen in liquid freon and then freeze dried, Seeds imbibed in soil were frozen in liquid nitrogen and then freeze dried. For LM, seeds imbibed over PEG were subjected to freeze substitution in dry acetone with 1% OSO4 at -80°C for 19 days.