The Collaborative International Dictionary of English v.0.48:

Inducer \In*du"cer\, n.
   1. One who, or that which, induces or incites.
      [1913 Webster]

   2. Specifically: (Genetics) A substance which, when it
      contacts a living cell, causes the activation of a gene;
      as, non-metabolizable inducers are useful for studying the
      kinetics of genetic control systems.
      [PJC]

WordNet (r) 3.0 (2006):

inducer
    n 1: an agent capable of activating specific genes
    2: someone who tries to persuade or induce or lead on [syn:
       persuader, inducer]