Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2007
Publication Date: 7/18/2007
Publication URL: http://www.springerlink.com/content/f4t492q07h32114j/?p=7419c2ce3d0444c7b3543ffc2bb66cad&pi=0
Citation: Korenkov, V., Hirschi, K., Crutchfield, J.D., Wagner, G.J. 2007. Enhancing tonoplast Cd/H antiport activity increases Cd, Zn, and Mn tolerance, and impacts root/shoot Cd partitioning in Nicotiana tabacum L. Planta. 226(6):1379-1387. Interpretive Summary: Metal accumulation in plants can be used to remove toxic compounds from polluted soils. Here we have engineered plants to express high levels of plant metal transporters so that the modified plants can accumulate increased amounts of metals. The result from this study is that we can make plants grow in environments that were previously toxic for plant growth. In addition, we can use these plants as a means to extract more pollutants from the soils. The novel plants created here can be used to cleanse the environment and increase the biomass of plants grown in sub-optimal environments.
Technical Abstract: Sequestration mechanisms that prevent high concentrations of free metal ions from persisting in metabolically active compartments of cells are thought to be central in tolerance of plants to high levels of divalent cation metals. Expression of "AtCAX2" or "AtCAX4", which encode divalent cation/proton antiporters, in "Nicotiana tabacum" cv. KY14 results in enhanced Cd- and Zn-selective transport into root tonoplast vesicles, and enhanced Cd accumulation in roots of plants exposed to moderate, 0.02 µM Cd in solution culture (Korenkov et al. in Planta 225:403–411, 2007). Here we investigated effects of expressing "AtCAX2" and "AtCAX4" in the same lines on tolerance to growth with near-incipient toxicity levels of Cd, Zn and Mn. Less growth inhibition (higher tolerance) to all three metals was observed in "35S::AtCAX2" and "FS3::AtCAX4" expressing plants. Consistent with the tolerance observed for Cd was the finding that while root tonoplast vesicle proton pump activities of control and FS3AtCAX4 expressing plants grown in 3 µM Cd were similarly reduced, and vesicle proton leak was enhanced, root tonoplast vesicle antiporter activity of these plants remained elevated above that in controls. We suggest that CAX antiporters, unlike tonoplast proton pump and membrane integrity, are not negatively impacted by high Cd, and that supplementation of tonoplast with AtCAX compensates somewhat for reduced tonoplast proton pump and proton leak, and thereby results in sufficient vacuolar Cd sequestration to provide higher tolerance. Results are consistent with the view that CAX2 and CAX4 antiporters of tonoplast play a role in tolerance to high, toxic levels of Cd, Zn, and Mn in tobacco.