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The magnetization reversal of Ni nanowires was studied by anisotropic magnetoresistance measurements at temperatures between 15 and 300 K. The wires, synthesized by electrodeposition in a nanoporous polycarbonate membrane, are regular cylinders 22 μm long with a diameter of 75 or 35 nm. The nucleation field was measured on individual nanowires as a function of the angle between the applied field and the wire axis. The results are quantitatively analyzed using classical magnetization reversal theories. Measurements of the nucleation field first obtained as a function of temperature evidence an extra uniaxial anisotropy induced by the contraction of the membrane at low temperature. Combining SQUID measurements and x-ray diffractometry at different temperatures, a clear picture of the large magnetoelastic effect was obtained.