KINETICS OF PHOSPHATE-UPTAKE IN EXCISED MAIZE ROOT

The short term uptake of phosphate involving 10 min absorption followed by 5 min desorption, both at 30 degrees C, in the concentration range 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 isotherm having five phases (0 and I - IV) with regularly spaced kinetic constants. Almost identical kinetics were observed in both fresh and washed 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 covered 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 evident in both fresh and washed maize roots. Each phase obeyed Michaelis - Menten kinetics. The values of K-m and V-max have been estimated for each phase. The uptake isotherm was accompanied by discontinuous transitions.