Measuring Intracellular Ca²⁺ Levels in Plant Cells Using the Fluorescent Probes, Indo-1 and Fura-2

Recent advances in the development of methods for measuring cytoplasmic Ca(2+) levels in higher plant cells are discussed. Emphasis is placed on the new generation of Ca(2+)-sensitive fluorescent dyes particularly fura-2 and indo-1. These dyes offer many advantages for the measurement of cytosolic Ca(2+) levels. They can be introduced into cells in a nonintrusive manner, their K(d) for Ca(2+) matches plant cell cytoplasmic Ca(2+) levels, and shifts in their emission (indo-1) or excitation (fura-2) spectra following Ca(2+) binding permit accurate quantitation of Ca(2+) activities. Examples of cytoplasmic Ca(2+) levels measured in plants with fura-2 and indo-1 are presented, and the prospects for applying more advanced technologies to fluorescent dye measurement are discussed.