Minisymposium 9: Global change

Abs # 22002: Modulation of cytosolic calcium pattern in stomatal carbon dioxide signal transduction

Presenter:	Young, Jared J., jyoung@biomail.ucsd.edu
Authors	Young, Jared J. (A)   Grill, Erwin  (B)   Schroeder, Julian I. (A)
Affiliations:	(A): Division of Biological Sciences, University of California, San Diego (B): Bot. Institut, Technische Universitat Munchen

Modulation of stomatal apertures by carbon dioxide, with high [CO₂] inducing stomatal closing and low [CO₂] inducing stomatal opening, is well-appreciated, but the signal transduction mechanisms that underlie these CO₂ responses are poorly understood. Because stomata are sensitive to [CO₂], the current large global increase in atmospheric [CO₂] being driven by human activity is likely to have a major effect on stomatal physiology. Furthermore, because CO₂ regulation of stomatal apertures during day/night periods impacts whole plant physiology, including such important parameters as carbon fixation rates, respiration, and water use efficiency, an enhanced understanding of the mechanisms underlying stomatal CO₂ responses would be desirable.

Repetitive increases in cytoplasmic calcium ([Ca²⁺]_cyt) have been shown to be important in many signal transduction processes, including stomatal closure in response to the drought stress hormone abscisic acid (Allen et al., 2001). Furthermore, guard cell CO₂ responses have been reported to be Ca²⁺-dependent. Thus we analyzed [Ca²⁺]_cyt during stomatal CO₂ responses using a protein-based “cameleon” calcium indicator. We observed that [Ca²⁺]_cyt elevations produced in Arabidopsis guard cells were modulated by high and low carbon dioxide, and that switching between CO₂ concentrations caused a corresponding modulation of [Ca²⁺]_cyt elevation patterns. These [Ca²⁺]_cyt elevations appear to be important for stomatal movements, since modifying extracellular calcium both affects the [Ca²⁺]_cyt elevations and prevents high CO₂-induced stomatal closure. Further genetic evidence for the importance of the [Ca²⁺]_cyt elevations comes from the ABA-insensitive gca2 mutant, which, unlike wildtype, does not alter the [Ca²⁺]_cyt pattern in response to changes in [CO₂] and impairs stomatal CO₂ responses. These observations suggest that modulation of the [Ca²⁺]_cyt pattern in guard cells is an important component of the stomatal response to changes in [CO₂].

Allen GJ, Chu SP, Harrington CL, Schumacher K, Hoffman T, Tang YY, Grill E, Schroeder JI. A defined range of guard cell calcium oscillation parameters encodes stomatal movements. Nature 411: 1053-1057 (2001)