The control of the Ca2+-ATPase gene (LCAl) that encodes two different mernbrane-located isoforms by two antagonic phytohormones, ABA and IAA, has been investigated. Strikingly both the growth regulators induce the LCA1 expression. By using a protoplast transient system, the cis-acting DNA elements responding to both, abiotic stress (ABA) and normal development (IAA), are dissected. ABA triggered a 4-fold increase in the GUS-activity. A single ACGT motif responsible for most of the LCAI mRNA induction was localized at an unexpectedly large distance (1577 bp) upstream of the translational start. In the case of IAA, although there is a TGTCTC sequence that is known to be an important cis-acting element, two TGA motifs play a more critical role. It is proposed that the Ca2+-ATPase isoforms might intervene in the generation of specific Ca2+ signals by restoring steady-state Ca2+ levels, modulating both frequency and amplitude of Ca2+ waves via wave interference. (C) 2005 Elsevier Inc. All rights reserved.