Abscisic acid stimulates the expression of two isoforms of plasma membrane Ca2+-ATPase in Arabidopsis thaliana seedlings

At-ACA8 and At-ACA9 are two plasma membrane (PM) Ca2+-ATPases of Arabidopsis thaliana. In this article the expression of At-ACA8, At-ACA9, and of At-ACA10, a third isoform of Ca2+-ATPase closely related to PM Ca2+-ATPases, was analysed and the effect of the hormone abscisic acid (ABA) on the expression level of PM Ca2+-ATPase specific transcripts was investigated. in adult plants of A. thaliana, At-ACA8 and At-ACA10 are expressed in all organs considered whereas At-ACA9 is expressed only in flowers. All isoforms of PM Ca2+-ATPases can be detected in young seedlings but the amount of At-ACA9 mRNA is much lower than those of At-ACA8 and At-ACA10. ABA markedly and rapidly stimulates the expression of both At-ACA8 and At-ACA9 genes in young seedlings but not that of At-ACA10. ABA also increases the level of At-ACA8 protein at the PM, suggesting a role for PM Ca2+-ATPases in ABA signalling.