Calcium channels and signal transduction in plant cells

An increasing number of studies indicate that changes in cytosolic free Ca 2+ ([Ca 2+ ] c ) mediate specific types of signal transduction in plant cells. Modulation of [Ca 2+ ] c is likely to be achieved through changes in the activity of Ca 2+ channels, which catalyse passive influx of Ca 2+ to the cytosol from extracellular and intracellular compartments. Voltage‐sensitive Ca 2+ channels have been detected in the plasma membranes of algae, where they control membrane electrical properties and cell turgor. These channels are sensitive to 1,4‐dihydropyridines, which in animal cells specifically affect one class of voltage‐regulated plasma membrane Ca 2+ channel. Ca 2+ ‐permeable channels with different pharmacological properties have been found in the plasma membrane of higher plants. Recent evidence suggests the existence of two discrete classes of Ca 2+ channel co‐resident in the vacuolar membrane (tonoplast) of higher plants. The first is gated by inositol 1,4,5‐trisphosphate, and bears a number of similarities to its animal counterpart which is located in the endoplasmic reticulum (ER). The second tonoplast Ca 2+ channel is voltage‐operated. However, the specific roles of these tonoplast channels in signal transduction have yet to be elucidated.