ASGSB 1998 Annual Meeting Abstracts

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ASYMMETRIC LOCALIZATION AND REDISTRIBUTION OF ANNEXINS IN GRAVISTIMULATED PEA PLUMULES.    G.B. Clark, M. Dauwalder, D.S. Rafati, and S.J. Roux. Department of Botany, Univ. of Texas, Austin.

Annexins are a multigene family of calcium-dependent, membrane- binding proteins which have been implicated in secretory processes, polar growth, and cell wall formation in plant cells. One of the signalling steps leading to gravitropism appears to require calcium and involve a redistribution of calcium across the region of tropistic bending. The gravitropic growth response is also known to involve the asymmetric secretion of new wall materials. An objective of our laboratory is to test a possible role for annexins in gravitropism. Using immunocytochemical techniques we investigated the effects of gravistimulation on annexin localization in etiolated pea shoots. In both longitudinal and cross-sections an asymmetric annexin immunostaining pattern was observed in groups of cells located in and close to a zone of cell differentiation just below the growing apex. This area has been traditionally referred to as the leaf gap. Some of the cells in this region show high levels of PAS staining in their cell wall. Changes in annexin localization were able to be detected within 15 minutes of gravistimulation. These data are the first to show annexins may be an early target of calcium action during the gravitropic response in plant shoots. (Supported by NASA: NAGW 1519).

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