Cellular mechanisms controlling light-stimulated gravitropism: role of calcium

An irradiation with visible light can alter the gravitropic responsiveness of shoots and roots. This indicates that light must affect some biochemical process in plant cells which is the same as, or importantly influences, a biochemical process that regulates gravitropism. In many cases, the light receptor for this effect is the pigment phytochrome, which initiates a variety of important photomorphogenic responses in plants. Recent results suggest that both gravistimulation and phytochrome photoactivation result in altered Ca²⁺ transport into and out of the affected cells. This article reviews the evidence that these Ca²⁺ fluxes may be the common biochemical process which modulates both gravitropism and photomorphogenesis.