HELIOTROPIC LEAF MOVEMENT RESPONSE TO H+ ATPASE ACTIVATION, H+/ATPASEINHIBITION, AND K+ CHANNEL INHIBITION IN-VIVO/

The pulvinus, located at the base of soybean leaflets, is both the lig ht perception and motor organ for heliotropic leaf movements. Our obje ctive was to investigate the role of plasma membrane H+/ATPase and TEA -sensitive K+ channels in mediating pulvinar response to light. The pl asma membrane H+/ATPase activator, fusicoccin, plasma membrane H+/ATPa se inhibitors, vanadate and erythrosin-B, and the K+ channel blocker T EA were introduced to the intact pulvinus through the transpiration st ream. The pulvinus was illuminated by a vertical light beam of 1,400 m u mol m(-2) s(-1) to stimulate leaf movement. Leaf orientation was mea sured every 5 min for 60 min of illumination. All compounds tested inh ibited pulvinar bending, but concentration and uptake time required fo r inhibition varied: 12.5 mu M fusicoccin reduced leaf movement after 3 hr uptake, 2 mM vanadate reduced leaf movement after 6 hr uptake, 10 0 mu M erythrosin-B reduced leaf movement after 3 hr uptake, and 15 mM TEA reduced leaf movement after 6 hr uptake. In all cases final leaf angle was reduced by higher concentrations and/or increased time for u ptake of the chemical into the pulvinus. Results support the hypothesi s that the proximal mechanism of heliotropic movement is similar to th at of nyctinastic movements.