ASGSB 1999 Annual Meeting Abstracts

CYTOSKELETON, CALCIUM AND pH DYNAMICS IN GRAVISTIMULATED BUNDLE SHEATH CELLS OF MAIZE PULVINI. N.S.Allen, E.Johannes, D.A.Collings, and J.C.Rink. Dept of Botany, North Carolina State University, Raleigh.

The presumptive statocytes in the maize stem pulvinus are amyloplast-containing bundles sheath cells that surround the vascular tissue. To investigate gravitropic signal transduction in the maize stem, we have developed a protocol with which to isolate protoplasts and partially digested files of cells from this bundle sheath tissue. These highly vacuolate cells contain numerous amyloplasts that distribute throughout the cell because of rapid, actin-based cytoplasmic streaming. In cell files, there was a net preference for the amyloplasts to sediment to the lower side of cells, and for slow plastid sedimentation to occur over several to many minutes after gravistimulation. However, plastid sedimentation is more pronounced and faster (under a minute) in protoplasts following re-orientation. Analysis of cells loaded with AM esters of calcium-sensitive dyes has shown no significant change in cytosolic calcium in the minutes immediately following gravistimulation. Similarly, loading of AM esters of pH-sensitive dyes demonstrates that amyloplast sedimentation does not correlate with observable changes in cytoplasmic pH, even though pH changes can be induced experimentally by weak acids. It remains possible that this lack of response is either due to disruption of tissue polarity during cell file production, or to the continual stimulation that the cells receive during this process. Therefore, we will use the experience and information gathered in these studies as the basis for further experiments based on the microinjection of pulvinal tissue slices.

Supported by NASA grant #NAGW-4984.

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