Annals of Botany Lecture
Roux, Stanley .
Signals that Regulate Germination and Polarized Growth in Pollen and Fern Spores.
The germination of both pollen and fern spores results in the emergence of a single cell—pollen tube from pollen; rhizoid from spore- that grows in a polar fashion, primarily at its apical end. In both of these tip-growing cells, the delivery of secretory vesicles to the growing end is guided in part by a calcium gradient, with calcium entering at the tip where it is most highly concentrated. Disruption of this gradient by calcium channel blockers disrupts polar growth in both cell types, and, in pollen, re-positioning sites of calcium entry changes the direction of polar growth. In both pollen tubes and primary rhizoids, annexin proteins, some of which may be acting as calcium channels, are concentrated at the growing tip. In spores of the fern Ceratopteris richardii that are germinating in a fixed orientation, the polarization of their development is directed by the vector of gravity within the first 18 h after light induces the spores to germinate. Gravity also directs a calcium current that enters the bottom of the spore and exits from the top. Inversion of the spore rapidly inverts the direction of the current, and blocking the current with calcium channel blockers disrupts the ability of gravity to direct the polarity of spore development. For the germination of both pollen and spores of Ceratopteris, the nitric oxide (NO) signaling pathway appears to play a critical role, for inhibitors of this pathway disrupt the process. Nitric oxide synthase is a calcium-regulated enzyme, and this connection may link the NO and calcium-signaling pathways. The interplay of these diverse signals in similar ways in both pollen and fern spores suggests these pathways became important regulators of germination and growth early in the evolution of land plants. (Supported by grants from NASA and NSF)
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1 - University of Texas at Austin, Section of Molecular Cell & Developmental Biology, 1 University Station A6700, Austin, Texas, 78712, USA
annexin, calcium, gravity.
Presentation Type: Special Presentation
Location: Salon J - Austin Grand Ballroom/Hilton
Date: Tuesday, August 16th, 2005
Time: 2:00 PM