Furthermore, transgenic Arabidopsis plants expressing a GUS-reporter gene under the control of the potato proteinase inhibitor II promoter (pinII) responded to several structurally different cyclic and acyclic monoterpenes (including b-ocimene) [16]. This is in line with the finding that six volatile terpenes increase the cytoplasmic free Ca2+ concentration in Arabidopsis leaf cells in a similar transient fashion [17]. Physicochemical processes, including interactions with odorant binding proteins and resulting in changes in transmem- brane potentials, can underlie VOCs-mediated signaling processes [18]. However, whether the volatile responses occur in a specific fashion remains to be answered.