  We analyze the effect of tensional strain in the electronic structure of
graphene. In the absence of electron-electron interactions, within linear
elasticity theory, and a tight-binding approach, we observe that strain can
generate a bulk spectral gap. However this gap is critical, requiring threshold
deformations in excess of 20%, and only along preferred directions with respect
to the underlying lattice. The gapless Dirac spectrum is robust for small and
moderate deformations, and the gap appears as a consequence of the merging of
the two inequivalent Dirac points, only under considerable deformations of the
lattice. We discuss how strain-induced anisotropy and local deformations can be
used as a means to affect transport characteristics and pinch off current flow
in graphene devices.
