Arabidopsis alcohol dehydrogenase expression in both shoots and roots is conditioned by root growth environment

It is widely accepted that the Arabidopsis Adh (alcohol dehydrogenase) gene is constitutively expressed at low levels in the roots of young plants gro wn on agar media, and that the expression level is greatly induced by anoxi c or hypoxic stresses. We questioned whether the agar medium itself created an anaerobic environment for the roots upon their growing into the gel. be ta-Glucuronidase (GUS) expression driven by the Adh promoter was examined b y growing transgenic Arabidopsis plants in different growing systems. Where as roots grown on horizontal-positioned plates showed high Adh/GUS expressi on levels, roots from vertical-positioned plates had no Adh/GUS expression. Additional results indicate that growth on vertical plates closely mimics the Adh/GUS expression observed for soil-grown seedlings, and that growth o n horizontal plates results in induction of high Adh/GUS expression that is consistent with hypoxic or anoxic conditions within the agar of the root z one. Adh/GUS expression in the shoot apex is also highly induced by root pe netration of the agar medium. This induction of Adh/GUS in shoot apex and r oots is due, at least in part, to mechanisms involving Ca2+ signal transduc tion.