Abstract
Uptake of phosphate ions by 1 mm segments of isolated maize root cortex layers was studied. Cortex segments (from roots of 8 days old maize plants) absorb phosphate ions from 1 mM KH2PO4 in 0.2 mM CaSCO4 at the average rate of 34.3 ±3.2 μg Pi g−1 (fr. m.) h−1,i.e. 0.35± 0.02 μmol Pi g−1 (fr. m.) h−1. Phosphate uptake considerably increases after a certain period of “augmentation”,i.e. washing in aerated 0.2 mM CaSO4. This increase is completely blocked by the presence of 10 μg ml−1 cycloheximide.
The relation of uptake rate to phosphate concentration in the medium was shown to have 3 phases in the concentration range of 0.02 - 40 mM. Transition points were found between 0.8–1 mM and 10–20 mM. Following Km and Vmax values were found: Km[mM] : 0.37 - 3.82 - 27.67 Vmax[μg Pi g−1 (fr. m.) h−1] : 3.33 - 39.40 - 66.67
We have found no sharp pH optimum for phosphate uptake. It proceeds at almost constant rate till pH 6.0 and then the uptake rate drops with increasing pH. At low phosphate concentrations (1 mM) the lowest uptake rate was found at 5 and 13 °C, while the uptake is higher at 5 °C than at 13 °C at phosphate concentrations higher than 1 mM. At these concentrations uptake rate at 35 °C is lower than at 25 °C.
Phosphate uptake considerably decreased in anaerobic conditions. DNP and iodoacetate (0.1 mM) completely blocked phosphate uptake from 1 mM KH2PO4, while uptake from 5 and 10 mM KH2PO4 was left unaffected by these substances. The inhibitors of active - SH groups NEM and PCMB inhibited phosphate uptake: 10−3 M NEM by 81.6%, 104 M NEM by 42% and 10−4 M PCMB by 42%.
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Abbreviations
- Pi :
-
inorganic phosphate
- DNP:
-
2,4-dinitrophenol
- NEM:
-
N-ethyl maleiimide
- PCMB(S):
-
p-chloromercuribenzoate (benzene-sulfonic acid)
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Macháčková, I., Král, J. & Zmrhal, Z. Characterization of phosphate absorption in maize root cortex segments. Biol Plant 25, 366–372 (1983). https://doi.org/10.1007/BF02878282
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DOI: https://doi.org/10.1007/BF02878282