title: The inhibition of ammonium uptake in excised birch (Betula pendula) roots by batatasin-III.
abstract: In northern Sweden, plants growing in association with the clonal dwarf shrub Empetrum hermaphroditum usually exhibit limited growth and are N-depleted. Previous studies suggest that this negative effect by E. hermaphroditum may be explained, at least in part, by the release of phenolic compounds, particularly the dihydrostilbene, batatasin-III from foliage to soil. In the present work, we investigated whether batatasin-III has the potential to interfere with NH4+ uptake in birch (Betula pendula) roots. Excised birch roots were exposed to batatasin-III during brief periods in 15NH4+ solutions, and then analyzed for labeled N. Batatasin-III inhibited N-NH4+ uptake by 28, 89 and 95% compared with the control, when roots were treated with 0.1, 1.0 and 2.8 mM of batatasin-III, respectively. The effect of 1.0-mM batatasin-III was greater at pH 4.2 than at pH 6.8. In addition, the inhibition of N-NH4+ uptake by batatasin-III was not reversed after rinsing the roots in water and transferring them to a batatasin-III free solution. Furthermore, birch seedlings immersed in a 1.0-mM batatasin-III solution for 2 h, and then replanted in pots with soil, had decreased growth, such that 10 weeks after treatment, the dry mass of both shoots and roots was reduced by 74 and 73%, respectively, compared with control seedlings. This suggests that a brief exposure to batatasin-III may have a long-term inhibitory effect on whole plant growth. Using plasma membrane vesicles isolated from easily extractable spinach (Spinacia oleracea) leaves, it was found that batatasin-III strongly inhibited proton pumping in isolated plasma membrane vesicles, while it only slightly inhibited ATP hydrolytic activity. The uncoupling of proton pumping from ATP hydrolytic activity suggests that batatasin-III disturbs membrane integrity. This hypothesis was further supported by a greater efflux of ions from birch roots immersed in a batatasin-III solution than from roots in a control solution.
authors.affiliation: Department of Ecology, Lund University, Lund, SE-223 62 Lund, Sweden Département des sciences du bois et de la forêt, Université Laval, Québec, G1K 7P4, Canada Department of Plant Biochemistry, Lund University, SE-221 00 Lund, Sweden Department of Forest Vegetation Ecology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Wallstedt
authors.forename: Marianne
authors.initials: M
authors.lastname: Sommarin
authors.forename: Marie-Charlotte
authors.initials: MC
authors.lastname: Nilsson
authors.forename: Alison D.
authors.initials: AD
authors.lastname: Munson
authors.forename: Hank A.
authors.initials: HA
authors.lastname: Margolis