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 (32)Pi from solutions of the same or different pH.Increasing pH of the absorption solution from 5.5 to 7.0 or 8.0 depressed (32)Pi 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 (32)Pi 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 (32)Pi 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 (32)Pi 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 (32)Pi absorption conflict with those for long-term P accumulation in plants.
Webb
M J
MJ
School of Environmental and Life Sciences, Murdoch University, Perth, Western Australia 6150.
Loneragan
J F
JF