Hint of polar distribution in calcium channels under PIXE analysis.

Pollen tubes ofLilium longiflorum were treated for 10-30 min with 10(-5) M CoCl2, which binds to calcium channels in the plasma membrane and blocks them. Cobalt analyses were performed with the Heidelberg proton microprobe, using 3 MeV protons, a beam current of about 200 pA, and a spot size of 3×5 µm(2). X-ray spectra revealed that coblat has much higher concentrations in the cell than in the surrounding dried medium. The line scans, taken along the longitudinal cell axis in 1-µm steps, showed a cobalt gradient similar to the calcium gradient of the same cell. Based on our findings, we can conclude that neither do the cobalt signals come from the cell wall nor is the cobalt exclusively bound to the intracellular calcium-binding sites. There-fore, the present results suggest a polar distribution in calcium channels in the plasma membrane of pollen tubes.