Poster: Intracellular Signaling

Abs # 836: Mitochondrial-targeted aequorin facilitates measurement of mitochondrial calcium dynamics in planta.

Presenter:	Logan, David C, david.logan@st-and.ac.uk
Authors	Logan, David C (A)   Knight, Marc R (B)   Hetherington, Alistair M (C)
Affiliations:	(A): University of St Andrews (B): University of Oxford (C): University of Lancaster
Web Site:	http://www.st-and.ac.uk/~dclogan

The role of mitochondrial Ca²⁺ in plant cell signalling has received little attention due to difficulties in measuring in vivo changes in mitochondrial Ca²⁺ concentration ([Ca²⁺]_m). This poster describes the unprecedented use of targeted aequorin to produce transformed Arabidopsis plants that enable analysis of mitochondrial Ca²⁺ dynamics in planta. Monitoring changes in cytoplasmic Ca²⁺ concentrations ([Ca²⁺]_cyt) in planta using the Ca²⁺ sensitive photoprotein, aequorin, has provided insights into our understanding of plant Ca²⁺ dynamics. This technique has been refined to offer greater resolution of cellular Ca²⁺ dynamics by targeting aequorin to specific subcellular locations. The data in this poster include the first direct measurements of the elevations in [Ca²⁺]_m resulting from physiological or environmental stimuli. Cold or osmotic stress led to an elevation in [Ca²⁺]_m, mirroring greater increases in [Ca²⁺]_cyt, which are most likely to have resulted from Ca²⁺ uptake from the cytosol into mitochondria. This suggests that mitochondria might be playing a role in buffering the [Ca²⁺]_cyt changes in response to these two stresses. However, the parallel rapid changes in [Ca²⁺]_m also provide a mechanism whereby the [Ca²⁺]_cyt could be modulated by different rates of uptake in different subcellular domains. The resulting spatial and temporal modulation of the Ca²⁺ signal could provide a fine-tuning mechanism enabling agonist specific signatures. Touch induced a [Ca²⁺]_m signature distinct from the [Ca²⁺]_cyt signature while oxidative stress elevated [Ca²⁺]_m to the same level as in the cytoplasm. Taken together the touch and oxidative stress induced perturbations indicate that there is a discriminating and autonomous mitochondrial Ca²⁺ signaling pathway in plant cells.