Control of Nitrate Uptake by Phloem-Translocated Glutamine in Zea mays L. Seedlings

Abstract

The putative role of glutamine, exported from leaves to roots, as a negative feedback signal for nitrate uptake was investigated in Zea mays L. seedlings. Glutamine (Gln) was supplied by immersion of the tip-cut leaves in a concentrated solution. Nitrate (NO₃ ^-) uptake was measured by its depletion in amino acid-free medium. The treatment with Gln resulted in a strong inhibition of nitrate uptake rate, accompanied by a significant enrichment of amino compounds in root tissue. The effect of N-availability on NO₃ ^- uptake was determined in split-root cultures. The plants were subjected to complete or localized N supply. Inducible NO₃ ^- uptake systems were also induced in N-deprived roots when the opposite side of the root system was supplied with KNO₃. The inhibitory effect of Gln was unaffected by localized N supply on one side of the split-root. The potential role of Gln in the shoot-to-root control of NO₃ ^- uptake is discussed.

Key words

Glutamine - maize roots - nitrate uptake - split-root cultures

References

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