NITRATE AND AMMONIUM UPTAKE BY WHEAT SEEDLINGS AS AFFECTED BY SALINITY AND LIGHT

Nitrate (NO3-) and ammonium (NH4+) are the two main forms of nitrogen (N) taken up by plants. Several environmental factors affect the uptak e of N. This work was undertaken to study the induction of NO3- and NH 4+ transport systems in wheat (Triticum aestivum L.) roots as affected by salinity and light. Wheat seedlings were germinated in sterilized vermiculite and plants were grown in a growth chamber under controlled conditions for eight days with a nutrient solution without N, and wit h or without sodium chloride (NaCl). Uptake rates of NO3-, NH4+,or NH4 + + NO3- were calculated by measuring the disappearance of N from the solutions. The NO3- uptake developed with time, either through inducti on or activation. Salinity pretreatments increased net uptake rates of NO3- and NH4+, suggesting that plants were in a higher N-deficient st atus when grown in saline conditions. Light decreased initial NO3- upt ake but had little effect on initial NH4+ uptake.