Poster: Membrane Transport

Abs # 287: The role of the root endodermis in ion uptake: Insights from T-DNA insertions in plasma membrane proton pumps

Presenter:	Baxter, Ivan , ibaxter@scripps.edu
Additional Authors	Harper, Jeffrey F (A)
Affiliations:	(A): Department of Cell Biology, The Scripps Research Institute, La Jolla, CA

The plasma membrane of plant cells is energized by an electrochemical gradient produced by P-type H+-ATPases (proton pumps). These pumps are encoded by at least 12 genes in Arabidopsis. T-DNA knockouts are being used to identify functions of individual isoforms. Previously, promoter/GUS reporter assays have shown isoform AHA4 to be expressed most strongly in the root endodermis and flowers [Vitart, et al. (2001) The Plant Journal, 27: 191]. A disruption of this pump (aha4-1) was identified as a T-DNA insertion in the middle of the gene. Plants homozygous for aha4-1 (-/-) show a dramatic reduction in rosette growth when grown under salt stress (e.g. 75 or 110 mM NaCl and KCl). This correlated with a 4-5 fold increase in the ratio of Na to K, as measured by ICP-AES. Interestingly, the aha4-1 mutation appears to be semi-dominant and was only partially complemented by the introduction of additional wild-type copies of AHA4. Here we present a characterization of a recessive aha4-2 allele, and two independent T-DNA disruptions of AHA4’s most closely related “sister-isoform” AHA11. For each homozygous mutant plant line, two of the phenotypes being evaluated are an increased sensitivity to salt and acid stress. In generating combinations of proton pump mutations, we have so far been unable to identify a plant line harboring homozygous disruptions of both AHA11 and AHA4, suggesting that these two isoforms together are essential.