Supersymmetry transformation of quantum fields

If supersymmetry is realized non-linearly as is the case when auxiliary fields are eliminated and/or one works in the Wess-Zumino gauge it is usually incorporated in terms of BRS transformations and Slavnov-Taylor identities. On the vertex functional susy transformations act even non-locally. Furthermore, the gauge fixing term breaks supersymmetry. In the present paper we clarify in which sense supersymmetry is still a symmetry of the system and how it is realized on the level of quantum fields. We treat the Wess-Zumino model as an example for chiral models, SQED and massless SYM as prototypes of gauge theories