EFFECTS OF KINETIN AND ABA ON PARAMETERS OF ROOT EXUDATION

We measured the kinetics of changes in the bleeding rate and osmotic p ressure of the bleeding sap on isolated pumpkin roots (Cucurbita maxim a L.) following introduction of kinetin (10(-11)-10(-5) M) Or ABA (10- 6-10-4 M) to the solution housing the roots. A biphasic nature is esta blished for the response to exogenous phytohormones. The first phase-s timulation of bleeding-is associated with increase of hydraulic conduc tance in the case of ABA or with increase in the flow of osmotically a ctive substances in the case of kinetin. The second phase-inhibition o f bleeding-is associated with reduction of hydraulic conductance and d ecline of substance flow during action of both phytohormones. It is hy pothesized that inhibition of bleeding is caused by closure of plasmod esmata and rapid decline in effective area of the inner root membrane (the x-membrane).