Uronide Deposition Rates in the Primary Root of Zea mays

The spatial distribution of the rate of deposition of uronic acids in the elongation zone of Zea mays L. Crow WF9 x Mo 17 was determined using the continuity equation with experimentally determined values for uronide density and growth velocity. In spatial terms, the uronide deposition rate has a maximum of 0.4 micrograms per millimeter per hour at s = 3.5 mm (i.e., at the location 3.5 mm from the root tip) and decreases to 0.1 mg mm(-1) h(-1) by s = 10 mm. In terms of a material tissue element, a tissue segment located initially from s = 2.0 to s = 2.1 mm has 0.14 mug of uronic acids and increases in both length and uronic acid content until it is 0.9 mm long and has 0.7 mug of uronide when its center is at s = 10 mm. Simulations of radioactive labeling experiments show that 15 min is the appropriate time scale for pulse determinations of deposition rate profiles in a rapidly growing corn root.