ASGSB 1999 Annual Meeting Abstracts

CALCIUM FLUXES INTO MOSS FILAMENTS FOLLOWING GRAVISTIMULATION. E. Johannes and N. S. Allen. Botany Department, North Carolina State University, Raleigh NC.

Dark grown caulonemal filaments of the moss Physcomitrella patens respond to gravistimulation with a reorientation of tip growth away from the gravity vector [1]. A self-referencing Ca²⁺ selective ion probe was employed to locate regions of net Ca²⁺ influx and efflux along the apical cell after reorientation of the filament from a vertical to a horizontal position. The experiments were performed in dim green and infrared light, which does not inhibit the gravitropic response. We found that growing caulonemal filaments exhibit a Ca²⁺ influx at the apical dome which is similar to that reported previously for other tip growing cells [2]. However, in gravistimulated Physcomitrella filaments the region of Ca²⁺ influx is not confined to the apex but extends about 60 µm along the upper side of the filament showing a maximum influx (in the range of 2.5 to 3.5 pmol cm^-2 s^-1) about 15 to 20 µm proximal of the apex. Our results indicate an asymmetry in the Ca²⁺ flux pattern between the upper and lower side of the gravistimulated filament suggesting differential activation of Ca²⁺ permeable channels at the plasma membrane (supported by NASA grant #NAGW-4984).

References:

[1] Knight, C. D. and Cove, D. J. (1991) The polarity of gravitropism in the moss Physcomitrella patens is reversed during mitosis and after growth on a clinostat. Plant Cell Environ. 14, 995-1001.

[2] Pierson, E. S., Miller, D. D., Callaham, D. A., van Aken, J., Hackett, G. and Hepler, P. K. (1996) Tip localized calcium fluctuates during pollen tube growth. Dev. Biol. 174, 160-173.

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