Cellular responses to endogenous electrochemical gradients in morphological development.

Endogenous electric fields give vectorial direction to morphological development in Zea mays (sweet corn) in response to gravity. Endogenous electrical fields are important because of their ability to influence: 1) intercellular organization and development through their effects on the membrane potential, 2) direct effects such as electrophoresis of membrane components, and 3) both intracellular and extracellular transport of charged compounds. Their primary influence is in providing a vectorial dimension to the progression of one physiological state to another. Gravity perception and transduction in the mesocotyl of vascular plants is a complex interplay of electrical and chemical gradients which ultimately provide the driving force for the resulting growth curvature called gravitropism. Among the earliest events in gravitropism are changes in impedance, voltage, and conductance between the vascular stele and the growth tissues, the cortex, in the mesocotyl of corn shoots. In response to gravistimulation: 1) a potential develops which is vectorial and of sufficient magnitude to be a driving force for transport between the vascular stele and cortex, 2) the ionic conductance changes within seconds showing altered transport between the tissues, and 3) the impedance shows a transient biphasic response which indicates that the mobility of charges is altered following gravistimulation and is possibly the triggering event for the cascade of actions which leads to growth curvature.