On the degree of curves with prescribed multiplicities and bounded negativity

We provide a lower bound on the degree of curves of the projective plane $mathbb{P}^2$ passing through the centers of a divisorial valuation $ u$ of $mathbb{P}^2$ with prescribed multiplicities, and an upper bound for the Seshadri-type constant of $ u$, $hat{mu}( u)$, constant that is crucial in the Nagata-type valuative conjecture. We also give some results related to the bounded negativity conjecture concerning those rational surfaces having the projective plane as a relatively minimal model.