Influence of coumarin on the net nitrate uptake in durum wheat

The effects are reported here of coumarin, an allelopathic compound, on root anatomy and growth, nitrate uptake and translocation to the shoot, as well as respiration in Triticum durum (cv. Simeto) seedlings. Wheat seedlings were grown in nitrogen-free hydroponic culture; after 6 d, coumarin (at concentrations of 0, 25 muM, 0.1, 1, 2.5 and 5 mM) and/or nitrate (50 muM) were added to the nutrient solution. Coumarin, in the range 25 muM-1 mM, decreased the relative growth rate of roots and increased the area of the root vessels. Within this concentration range, coumarin alone did not significantly affect net nitrate uptake. In seedlings exposed simultaneously to 100 muM coumarin and to 50 muM nitrate, the net nitrate uptake was significantly stimulated. In the presence of nitrate, even the lowest coumarin concentration tested significantly stimulated nitrate translocation from the root to the shoot. The effects of low coumarin concentrations on root vessel size could explain this observation, though specific interactions between coumarin and systems regulating nitrate uptake and transport within the root cell cannot be excluded. (C) New Phytologist (2001).