Studies on Leaf Orientation Movements in Kidney Beans(Phaseolus vulgaris L.). IV. Effect of water spray on leaflet inclination.

Abstract

Leaflet movements in response to a reduction of leaf temperature by water spray was examined under severe plant water stress at fine midday, using the lateral leaflets of the third trifoliolate leaves in potted plants of two kidney bean (Phaseolus vulgaris L.) cultivars : Hime-tebo and Taisho-kintoki. All lateral leaflets not sprayed with water (the control) largely inclined and oriented themselves to their terminal leaflet. The water spray (the spray treatment) rapidly decreased the twisting angles of the leaflets, but did not change the vertical angles. In the control, stomata closed completely (except for abaxial surface of cv. Taisho-kintoki) and water saturation deficit was much higher. However, in the spray treatment, although not significant, the stomata of leaflets slightly opened and the water saturation deficit rose rather slightly. The decrease of the twisting angle synchronized with a reduction of leaf temperature. The change in the twisting angle of the lateral leaflets seemed to be associated with leaf temperatures, not with leaf water potentials. Further, this response was discussed to be caused directly by the change in temperature of the pulvinule rather than the leaf blade.