Nonuniform Transport of Phosphorus from Single Roots to the Leaves of Zea mays

The postulate that single roots of Zea mays transport their absorbed phosphorus nonuniformly to the leaves was tested. Plants were grown under growth chamber conditions for three to four weeks in nutrient solution. At this stage of growth a series of plants was placed into a system in which two roots on each plant were allowed to absorb either ³³P or ³²P from uptake solutions for time intervals of up to 24 hours. Plants subsequently were harvested such that each leaf was partitioned into samples containing tissue from one side or the other of the midrib. All samples were assayed for ³³P and ³²P and the results were expressed as the amount of total P transported into different plant parts from a single root. Nonuniform P accumulation in the leaves occurred and different patterns of accumulation, dependent on the type of root chosen for uptake were observed. Nearly uniform P accumulation occurred between one side and the other of a given leaf when transport was from radicle roots. In marked contrast, transport from adventitious roots resulted in an alternating pattern of accumulation between one side and the other of each successive leaf up the stem. The seminal root system supplied more P to the older leaves than did the adventitious root system. The nature of these nonuniform P transport patterns is attributed to the vascular organization between roots and leaves.