The roles of light and the nucleus in the regulation of reproductive onset in Acetabularia acetabulum |
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Authors: | René F Kratz Dina F Mandoli |
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Institution: | (1) Department of Botany, Box 355325, University of Washington and Center for Developmental Biology, Seattle, WA 98195, USA, US |
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Abstract: | At reproductive onset the marine green alga Acetabularia acetabulum (L.) P.C. Silva redirects growth from vertical elongation of the axis of the plant to lateral expansion of a disk-shaped
reproductive structure, the “cap.” We used amputation to synchronize cap initiation and to facilitate investigation of the
light requirements during amputation-induced cap initiation. Following amputation of a nascent cap, most plants initiate one
whorl of vegetative hairs and then a cap. Both hair and cap initiation required photosynthesis, as indicated by studies with
3-(3′,4′-dichlorophenyl)-1, 1-dimethylurea, but did not require the nucleus. Amputation-induced hair initiation occurred in
red light, but 10 min of blue light given in a background of red light significantly increased hair initiation, supporting
previous studies that hair initiation is a blue-light-triggered photomorphogenic event. Amputation-induced cap initiation
also occurred in red light, but daily 10-min flashes of blue light given in a background of red light did not significantly
enhance cap initiation. We also examined the light requirements of intact plants at each phase of development. In the absence
of blue light, juveniles and adults with ≤13.7 ± 4.3 whorls of hairs arrested in development and failed to initiate caps.
In contrast, very late adults with ≥13.7 ± 4.3 whorls of hairs initiated caps in the absence of blue light, suggesting that
there is a point in late adult development beyond which cap initiation does not require blue light. Several plausible interpretations
of the role of light and the nucleus in the regulation of reproductive onset are discussed to try to reconcile these data
with those in the literature.
Received: 18 March 1999 / Accepted: 13 May 1999 |
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Keywords: | Key words:Acetabularia Morphogenesis Phase change Photobiology Reproductive onset |
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