Poster: Signaling, cell-to-cell

Abs # 449: Calcium dynamics within elongating conifer pollen tubes differ from that seen in flowering plants.

Presenter:	Lazzaro, Mark D, lazzarom@cofc.edu
Authors	Lazzaro, Mark D (A)   Bhatt, Aadra P (A)   Cardenas, Luis  (B)   Hepler, Peter K (B)
Affiliations:	(A): College of Charleston (B): University of Massachusetts
Web Site:	http://www.cofc.edu/~lazzaro

Pollen tubes deliver sperm cells to the egg for fertilization in higher plants and are a model system for examining polarized cell growth. Rapidly elongating flowering plant pollen tubes require an influx of extracellular calcium which generates a steep, tip-focused cytoplasmic calcium gradient. Organelles move in a microfilament-myosin dependent reverse fountain into the tip. Conifer pollen tubes grow much slower and organelles move in an unusual fountain pattern into the tip. This pattern is controlled by microfilaments and myosin but is orchestrated by microtubules since microtubule disruption causes the pattern to switch direction into a reverse fountain (Justus, Anderhag, Goins, Lazzaro; Planta 2004). Using Picea abies (Norway spruce), we find that conifer pollen tubes also contain a weak, 2-fold tip focused calcium gradient, much less than in flowering plants. The gradient is dissipated by cytoplasmic injection of BAPTA or by reversible perfusion of extracellular caffeine. However, the basal calcium concentration in the cytoplasm also drops and triggers a large influx of extracellular calcium, which has not been seen in flowering plant systems. This influx causes a surge in elongation and alters organelle motility within the tip. Extracellular perfusion of lanthanides reversibly depletes the cytoplasmic calcium gradient. However, organelle motility also switches direction to a reverse fountain. Our model is that slower growing conifer pollen tubes normally require a weak influx of extracellular calcium and an elevated basal calcium level. When this basal level is diminished, calcium channels open at the plasma membrane. The unusual calcium dynamics in these cells also contributes to organizing the unusual pattern of organelle motility within the elongating tip.