Kinetics of phosphate uptake in excised maize root

Abstract

The short term uptake of phosphate involving 10 min absorption followed by 5 min desorption, both at 30 °C, in the concentration range 1.0×10-9 to 7.5×10-2 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 1.0×10-9-3.0×10-5 M. was sigmoidal in fresh maize roots, however, in washed tissue exhibited 2 phases termed here as 0a and 0b. 0a covered the concentration range 1.0×10-9-5.0×10-6 M and 0b 6.0×10-6-3.0×10-5 M. In the concentration range 1.0×10-4-7.5×10-2 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 Km and Vmax have been estimated for each phase. The uptake isotherm was accompanied by discontinuous transitions. © 1995 Institute of Experimental Botany, ASCR.