PHYSIOLOGICAL-RESPONSES OF LUPIN ROOTS TO HIGH PH

High pH seems to be a major constraint limiting the production of narr ow-leafed lupin (Lupinus angustifolius L.) on alkaline soils. Whereas there has been much interest in soil acidity, relatively little is kno wn about the effect of high pH on the growth of roots of higher plants . Elongation of roots of L. angustifolius was particularly sensitive t o pH equal to or greater than 6.0 compared with other species. The eff ect of high pH in decreasing root elongation in L. angustifolius occur red within one hour. It was via an effect on cell elongation and not c ell division and the effect was readily reversible. The mechanisms of the adverse effect of high pH are unknown. The permeability ratio of K + to Naf in the plasma-membrane of the root cortical cells was similar in solutions of both low pH and high pH. Reduced cell growth at high pH was not associated with an inefficiency of proton extrusion to the bulk solution by roots of this species. Nevertheless, increasing buffe r concentration in the external solution decreased root elongation mor e in L. angustifolius than in Lupinus pilosus and Pisum sativum.