Influence of Ni Supply on Growth and Nitrogen Metabolism ofBrassica napusL. Grown with NH4NO3or Urea as N Source

The significance of nickel (Ni), which is essential for ureaseactivity, for growth and nitrogen (N) metabolism ofBrassicanapusgrown in nutrient solution with either NH₄NO₃or urea assole N source was investigated. Although Ni contents were below25 µg kg^-1d. wt, growth of plants relying on NH₄NO₃wasnot affected by the Ni status. However, supplementing the growthmedium with 0.04 µMNi enhanced dry matter production ofurea-grown plants significantly. Urease activity was significantlyreduced in leaves and roots of plants grown without supplementaryNi irrespective of N source. Plants grown with urea withoutadditional Ni accumulated large amounts of urea and had loweramino acid contents indicating impaired usage of the N supplied,while those grown with NH₄NO₃under Ni-deprived conditions accumulatedendogenous urea in their older leaves. It is suggested thatNi may not be strictly essential for plants receiving mineralN, or that the critical level is well below 25 µg kg^-1d.wt. These results confirm that Ni is required for urease activityand thus for growth of plants on urea-based media, as well asfor recycling endogenous urea.Copyright 1999 Annals of BotanyCompany. Brassica napusvar.annua, amino acids, N nutrition, nickel, spring rape, urea, urease activity.