Influence of coumarin on the net nitrate uptake in durum wheat

The effects are reported here of coumarin, an allelopathic compound, on roo t anatomy and growth, nitrate uptake and translocation to the shoot, as wel l 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 nitr ate (50 muM) were added to the nutrient solution. Coumarin, in the range 25 muM-1 mM, decreased the relative growth rate of r oots and increased the area of the root vessels. Within this concentration range, coumarin alone did not significantly affect net nitrate uptake. In s eedlings exposed simultaneously to 100 muM coumarin and to 50 muM nitrate, the net nitrate uptake was significantly stimulated. In the presence of nit rate, even the lowest coumarin concentration tested significantly stimulate d nitrate translocation from the root to the shoot. The effects of low coumarin concentrations on root vessel size could explai n this observation, though specific interactions between coumarin and syste ms regulating nitrate uptake and transport within the root cell cannot be e xcluded. (C) New Phytologist (2001).