Rasmussen, J., Gilroyed, B. H., Reuter, T., Badea, A., Eudes, F., Graf, R., Laroche, A., Kav, N. N. V. and McAllister, T. A. 2014. Efficiency of protein as a nitrogen source for wheat and morphological changes in roots exposed to high protein concentrations. Can. J. Plant Sci. 94: 603-613. Proteins of animal origin can enter the environment through application of agricultural by-products to arable or pastured land. In this study, wheat (Triticum aestivum cv. AC Andrew) was exposed to treatments with nitrogen (N) supplied as animal protein (bovine serum albumin; BSA), inorganic N or a combination of these sources at different iso-nitrogenous concentrations. Plant growth was assessed by monitoring both wet and dry mass of shoots and data showed that protein treatments did not differ (P>0.05) from controls lacking N. Analysis of N also showed that plants supplied with protein N displayed lower N (1.2-2.4%) concentration as compared with those supplied with inorganic N (up to 12.4%) with N remaining <2.4% even when the supply of protein was increased. Root morphology was altered in plants exposed to protein N concentrations >71 mM, with the development of knob-like outgrowths with unknown function or significance. This study provides evidence that wheat plantlets grown under sterile conditions are unable to utilize BSA as efficiently as NH₄NO₃ as a N source, but their roots exhibit a morphological response to protein.