Nitrate Accumulation and Osmotic Regulation in Italian Ryegrass (Lolium multiflorumLam.)

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Abstract
The role of nitrate accumulation was studied in osmotic adaptation of Italian ryegrass (Lolium multiflorum Lam. cv. Romo). Plants were grown under different light intensities (68 and 143 W m−2) and on Hoagland nutrient solution with a solute potential of 0.035 MPa and −0.335 MPa. The solute potential of the nutrient solution was decreased by addition of NaCl, which was taken up by the plant, and PEG 6000 which was not. At each growing condition the solute potential of the expressed plant sap was constant during the experimental period of 19 d, but was decreased by increase in light intensity and addition of osmotic substances in the root medium. At sugar concentrations between 20 and 60 mg per gram plant water a change in sugar concentration is osmotically fully compensated for by an opposite change in nitrate concentration. At sugar concentrations lower than 20 mg per gram plant water there is an overcompensation of nitrate. The overcompensation increase is attributed to a concomitant decrease of other organic solutes such as amino acids and organic acids. When NaG is added to the nutrient solution, the nitrate concentration in the plant decreases and the solute potential is decreased by uptake of chloride. With PEG the nitrate content of the plant also decreased. The solute potential of the plant sap is decreased by accumulation of sugar, at least at the high light intensity.

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