Blue Light Inactivates Plasma Membrane H+-ATPase in Pulvinar Motor Cells of Phaseolus vulgaris L.

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Abstract
Unilateral blue light irradiation induces bending of pulvini of Phaseolus vulgaris towards the source of light. The pulvinar bending is caused by a decrease in turgor pressure of motor cells that are irradiated with blue light. Decrease in the turgor pressure is caused by the net efflux of K+ and counter anions, accompanying membrane depolarization. In the present study the effect of blue light on the activity of plasma membrane H+-ATPase was studied in relation to the membrane depolarization. The activity of the plasma membrane H+-ATPase was measured using protoplast suspensions prepared from laminar pulvini from primary leaves. A pulse of blue light under continuous red light irradiation induced both a transient increase in the external pH and transient inhibition of the vanadate-sensitive ATPase. Continuous blue light irradiation under continuous red light irradiation induced both a sustained increase in the external pH and sustained inhibition of the vanadate-sensitive ATPase. These results show that blue light inhibits the activity of the plasma membrane H+-ATPase. Inactivation of the plasma membrane H+-ATPase supports the membrane depolarization induced by the blue light irradiation.

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