Phosphate absorption by air-stressed root systems

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Abstract
Root systems from plants grown in nutrient solution were exposed to air and either transferred to fresh nutrient solution containing 32P-labeled phosphate or placed in a psychrometer to determine their water potential. The amount of 32P absorbed by maize and soybean roots in the hour following their exposure to air was proportional to their water potential at the time they were transferred. Some cells, probably located in the stele, were more resistant to moisture stress than others. Absorption of 32P by all cells was severely inhibited by water potentials below-12 to-15 bars. Nearly normal amounts of the radioisotope and total phosphate were absorbed within 72 hr following root exposure of 4 of 5 species of detopped plants; some phosphorus was lost to the nutrient solution. Uptake of 32P by passive processes was increased slightly by exposure of roots of intact maize plants to air, but the increase did not compensate for the substantial reduction in actively-absorbed 32P.