Poster: Tropisms

Abs # 659: Plastid position in endodermal cells of Arabidopsis seedlings: implications for models of graviperception

Presenter:	Kiss, John Z., kissjz@muohio.edu
Authors	Kiss, John Z. (A)   Palmieri, Maria  (A)
Affiliations:	(A): Botany Department, Miami University, Oxford OH 45056, USA

Plants possess statocytes, which are specialized cells containing dense organelles (i.e., amyloplasts) that are hypothesized to play a key role in gravity perception mechanisms. In numerous studies, amyloplast position has been examined in statocytes after exposure to a variety of gravity conditions (e.g., vertical, reorientation, clinostat, microgravity). Analyses of several different plant species grown during spaceflight experiments indicate that amyloplasts do not attain random positioning in the root statocytes (= columella cells) under microgravity. Rather, amyloplasts remain clustered and migrate to the geometric center of these cells. Although the cause of this nonrandom positioning is unknown, it has been proposed that plastid attachment to the actin cytoskeleton may play a role in this process. In the present study, we examine amyloplast position in hypocotyl statocytes (= endodermal cells) of wild-type and starch-deficient mutants of Arabidopsis grown in microgravity conditions as part of a study performed on Space Shuttle flight STS-84. In these experiments, there also was an in-flight 1-g control along with appropriate ground controls. We will determine if our results support a previous model for the modulation (via the cytoskeleton) of amyloplast responsiveness in statocytes to inertial acceleration. While there have been numerous experiments with roots, this is one of the first studies to examine plastid position in statocytes of stem-like organs in microgravity. [This work was supported by NASA grant NCC2-1200.]