Importance of Environmental pH during Root Development on Phosphate Absorption

Wheat seedlings (Triticum aestivum L. cv Gamenya) were grown for 4 days in culture solutions of differing pH prior to studying their subsequent short-term absorption of ³²Pi from solutions of the same or different pH.

Increasing pH of the absorption solution from 5.5 to 7.0 or 8.0 depressed ³²Pi absorption from 1 and 10 micromolar Pi but had little effect at 100 and 1000 micromolar Pi. Increasing the pH of the culture solution from 4.5 to 6.5 doubled or trebled subsequent ³²Pi absorption from nearly all absorption solutions over a wide range of Pi concentrations, pH, and nutrient compositions.

When seedlings were transferred between culture pH treatments 4.5 and 6.5, their capacity for ³²Pi absorption remained unchanged for at least 5 hours and adjusted by 60 to 80% after 24 hours and completely after 48 hours. This suggests that the root's capacity to absorb Pi responds to pH through slow structural changes in its mechanism of Pi absorption. P content and concentration of wheat seedlings reflected the response of ³²Pi absorption to culture pH.

It is suggested that absorption pH affects an activity component of the process for Pi absorption and culture pH affects a capacity component. Failure to recognize the capacity component of the pH response explains why previously published results for short-term ³²Pi absorption conflict with those for long-term P accumulation in plants.