PLANT PHYSIOLOGY , Vol 115, Issue 2 683-692, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
A Secreted Factor Inducs Cell Expansion and Formation of Metaxylem-Like Tracheary Elements in Xylogenic Suspension Cultures of Zinnia
A. W. Roberts, S. G. Donovan and C. H. Haigler
Department of Biological Sciences, University of Rhode Island, 10 Ranger Road, Kingston, Rhode Island 02881 (A.W.R, S.G.D.)
Conditioned medium from mesophyll cell-suspension cultures of Zinnia
elegans L. has striking effects on cell expansion and tracheary element
differentiation when applied to cultures of freshly isolated mesophyll
cells. These effects include (a) induction of early cell expansion, (b)
delay in differentiation by 48 h or more, (c) reduction in the synchrony of
differentiation, and (d) early formation of very large, metaxylem-like
tracheary elements. Like reduced osmotic potential and buffering at pH 5.5,
conditioned medium appears to have its primary effect on cell expansion.
Partial characterization of the expansion-inducing factor indicates that it
is heat stable, of low molecular mass, and is resistant to protease. It
also binds reversibly to concanavalin A but is not adsorbed by charcoal. We
suggest that the secreted factor may be an oligosaccharide involved in the
coordination of cell expansion and differentiation and the regulation of
the protoxylem-like to metaxylem-like transition in xylogenic suspension
cultures.
