Probing Cytosolic [Ca2+] as Signal Transducer using Fluorescent Dyes

Many of the techniques developed for measuring intracellular Ca in animal cells cannot be readily applied to plant cells. Because of rigid cell wall, wall-associated esterase activities and turgor pressure of plant cells, conventional methods for introducing probes into the cytoplasm are ineffective. Several popular fluorescent Ca indicators are rapidly sequestered into the plant vacuole, resulting both in loss of probe from the cytoplasm as well as in erroneous measurements. Autofluorescence from the plant cell walls and chloroplasts can also severely limit the detectability of fluorescent probes. The present article provides information on the selection criteria for various fluorescent Ca probes, excited by ultraviolet irradiation, visible light and aequorin - a bioluminescent Ca indicator. Recent cloning of apoaequorin cDNA has permitted many new uses of this photoprotein, including its ability to express in specific cells and subcellular structures.