Poster: Tropisms

Abs # 667: Simultaneous measurement of proton and calcium fluxes surrounding Arabidopsis roots before and after gravistimulation

Presenter:	Allen, Nina S
Authors	Xu, Yue  (A)   Johannes, Eva  (A)   Allen, Nina S (A)
Affiliations:	(A): North Carolina State University
Web Site:	http://cmif.bot.ncsu.edu/cmif

In columella cells of Arabidopsis thaliana roots we and others previously found that cytoplasmic pH (pHc) changes in response to gravistimulation and that pHc is a mediator in early gravitropic signaling (AC Scott, NS Allen [1999] Plant Physiol 121: 1291-1298), JM Fasano et al [2001] Plant Cell 13: 907-92). Detecting changes in Ca²⁺ has been more of a challenge. We have measured proton and calcium fluxes surrounding 3-4 day old Arabidopsis roots at the tip and at the elongation zones using non-invasive ion selective probes over time before and after gravistimulation. Measurements were made using two probes simultaneously while imaging the roots in the x/y (bottom view) and y/z axis (side view) in a newly designed 3D measurement chamber. Gravistimulated roots started bending around 30 mins. Oscillations of H⁺ and Ca²⁺ fluxes occurred in both the tip and elongation zones regardless whether roots were gravistimulated or not. Whereas control roots exhibited a symmetrical pattern of H⁺ and Ca²⁺ fluxes we found that after gravistimulation the flux pattern became asymmetric: We observed an increase in H⁺ efflux and an increase in Ca²⁺ influx in both the lower flank of the tip region and the upper flank of the bending elongation zone. The results suggest that differential proton and calcium ion fluxes are involved in gravity perception and response in these roots.