Effects of modulation of calcium levels and calcium fluxes on ABA-induced gene expression in barley aleurone

We present data to elucidate the involvement of calcium ions in abscisic acid (ABA)-induced gene expression. Modulation of external calcium concentrations was able to affect ABA-induced specific RAB gene expression. At a constant ABA level with increasing extracellular calcium level, an increasing RAB mRNA expression was measured. In barley aleurone protoplasts, RAB gene expression was inhibited by blockers of the calcium channel and outward rectifying potassium channel (verapamil and bepridil). The inhibitory effects were dependent on the concentrations of blockers applied. The possible role of calcium in ABA-regulated gene expression in aleurone protoplasts was further analyzed by using calmodulin inhibitors and the Ca2+ antagonists Cd2+ and La3+, which showed a strong inhibition on RAB gene expression. In addition, indirect manipulation of the inositol cycle by using Li+ showed a dramatic stimulation of ABA-induced gene expression. Introducing inositol [1,4,5]-trisphosphate (InsP(3)) into protoplasts had strong inhibitory effects on ABA-induced RAB gene expression, whilst addition of heparin could overcome this inhibitory effect. Based on these results, a possible role of calcium fluxes and intracellular calcium levels in ABA signal transduction is discussed.