UPTAKE, TRANSPORT AND METABOLISM OF PHOSPHATE BY INDIVIDUAL ROOTS OF ZEA-MAYS L

The root system of 21 day old maize plants is formed by three differen t types of roots. The seminal root system, primary seminal (PS) and se minal adventitious roots (SA) represent 52.48%, and nodal roots (N) re present 47.52%, of the total root mass. Phosphate absorption and parti cipation of individual roots in the total phosphate uptake increase in the following order: PS < SA < N. More than half of the total phospha te taken up by individual roots was found in the fraction of inorganic phosphate. Incorporation of P-32 into organic low molecular weight ph osphate compounds and free nucleotides increased in the order of PS < SA < N, and decreased in the same order in the macromolecular phosphat e compounds. Phosphate taken up by seminal roots was quickly transport ed to the shoot. The amount of phosphate transported from seminal root s was two times higher than from the nodal ones. In primary seminal an d seminal adventitious roots the water movement occurred in the protox ylem and early and late metaxylem vessels. In the nodal roots only a s mall amount of late metaxylem vessels were involved in water transport .