KINETICS OF PHOSPHATE-UPTAKE IN EXCISED MAIZE ROOT

The short term uptake of phosphate involving 10 min absorption followe d by 5 min desorption, both at 30 degrees C, in the concentration rang e 1.0 x 10(-9) to 7.5 x 10(-2) M KH2PO4 by fresh and washed maize (Zea mays L. cv. Ganga Safed-2) roots can be described by a single isother m having five phases (0 and I - IV) with regularly spaced kinetic cons tants. Almost identical kinetics were observed in both fresh and washe d maize roots. The kinetics of phase 0 in the concentration range 1.0 x 10(-9) - 3.0 x 10(-5) M was sigmoidal in fresh maize roots, however, in washed tissue exhibited 2 phases termed here as Oa and Ob. Oa cove red the concentration range 1.0 x 10(-9) - 5.0 x 10(-6) M and Ob 6.0 x 10(-6) - 3.0 x 10(-5) M. In the concentration range 1.0 x 10(-4) - 7. 5 x 10(-2) M four distinct phases, termed as I, II, III and IV were ev ident in both fresh and washed maize roots. Each phase obeyed Michaeli s - Menten kinetics. The values of K-m and V-max have been estimated f or each phase. The uptake isotherm was accompanied by discontinuous tr ansitions.