ASGSB 1999 Annual Meeting Abstracts

A RE-INVESTIGATION OF ACTIN ORGANIZATION IN THE COLUMELLA CELLS OF HIGHER PLANTS. G.Zsuppan, D.A.Collings, and N.S.Allen. Dept. of Botany, North Carolina State University, Raleigh.

In a recent review of the cytoskeleton and gravitropism, it was proposed that the columella cells of higher plant root caps have few actin bundles, in part to allow for the more rapid sedimentation of amyloplasts during gravisensing [Baluska and Hasenstein (1997) Planta 203: s69-s73]. By contrast, we have observed that gravisensing bundle sheath cells in maize pulvini contain extensive actin bundles organized into patterns similar to those in neighboring, non-gravisensing cells [Collings et al. (1998) Planta 207: 246-258]. Because our observations in pulvini suggest that either the reduced actin hypothesis is flawed, or that it is not general to all higher plant cells, we re-investigated the actin cytoskeleton in root cap cells of Zea mays using confocal immunofluorescence microscopy. Polyclonal and monoclonal antibodies gave extensive (and similar) labelling of F-actin in the elongation zone and meristem, and in peripheral root cap cells. Extensive labeling of actin is also present within the columella, although the degree of bundling and the relationship of this actin to the amyloplasts has been difficult to determine.

While similar immunofluorescence investigations of Arabidopsis thaliana root caps have not yet been possible, confocal visualization of transgenic plants expressing ER-targeted green fluorescent protein demonstrates that columella cells exhibit cytoplasmic streaming and that these cells contain actin bundles. Similar observations have also been made in the columella cells of Nicotiana benthamiana.

Taken together, these results indicate that the columella cells of higher plants most likely have an actin cytoskeleton similar to those in other cells types. Potential roles for this actin in gravisensing are currently being investigated.

(Supported by NASA grant #NAGW-4984.)

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