  The nucleosynthesis in the first massive stars may be constrained by
observing the surface composition of long-lived very iron-poor stars born
around 10 billion years ago from material enriched by their ejecta. Many
interesting clues on physical processes having occurred in the first stars can
be obtained just based on nuclear aspects. Two facts are particularly clear, 1)
in these first massive stars, mixing must have occurred between the H-burning
and the He-burning zone during their nuclear lifetimes; 2) only the outer
layers of these massive stars have enriched the material from which the very
iron-poor stars, observed today in the halo, have formed. These two basic
requirements can be obtained by rotating stellar models at very low
metallicity. In the present paper, we discuss the arguments supporting this
view and illustrates the sensitivity of the results concerning the [Mg/Al]
ratio on the rate of the reaction Na(23)(p,\gamma)Mg(24).
