Poster: Tropisms

Abs # 418: Role of calcium transporters in the touch and gravity responses of Arabidopsis roots

Presenter:	Swanson, Sarah J., sjs31@psu.edu
Authors	Swanson, Sarah J. (A)   Gilroy, Simon  (A)
Affiliations:	(A): Penn State University, University Park PA 16865

Roots can combine gravitropic and thigmotropic information to yield an appropriate integrated growth response. Although it appears that touch stimulation can down-regulate the gravity response, the molecular mechanism for this signal integration remains poorly defined. We have therefore examined the potential role of ionic signaling in mediating this signal processing. Touch stimulation of the peripheral cells of the root cap elicited an increase in cytosolic Ca²⁺ that propagates from cell to cell throughout the cap. This observation supports the idea that the Ca²⁺ homeostatic system is altered when a root encounters an obstacle. We therefore have screened a T-DNA insertional library consisting of multiple alleles of all putative Arabidopsis Ca²⁺ pumps for effects on the responsiveness of their roots to growth along a solid barrier. The wild type response is characterized by the establishment of a fixed angle of the root tip relative to the barrier. Mutants altered in this response may help identify Ca²⁺ transporter systems involved in mediating the touch and/or gravity signaling response. The spectrum of Ca²⁺ transporter mutants showed a range of angles as the roots track along the barrier. While the majority of mutants, such as cax1-1, established an angle similar to wild type (32.4±5.5^o), a few maintained a steeper angle (e.g. the double mutant aca12-1/13-1, 52.8±5.2^o) or grew flat along the barrier (e.g. aca11-2, 18.6±1.8^o). Touch-induced calcium changes in these mutants are currently being investigated. These results suggest that calcium pumps play an important role in the Ca²⁺-dependent touch signaling system, which ultimately results in an appropriate tropic growth response. This work was supported by grants from NASA and NSF.