PLANT PHYSIOLOGY , Vol 115, Issue 4 1599-1607, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Phloem-Specific Expression of the Tobacco Mosaic Virus Movement Protein Alters Carbon Metabolism and Partitioning in Transgenic Potato Plants
E. Almon, M. Horowitz, H. L. Wang, W. J. Lucas, E. Zamski and S. Wolf
Department of Field Crops, Vegetables, and Genetics and the Otto Warburg Center for Agricultural Biotechnology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel (E.A., M.H., S.W.)
The tobacco mosaic virus movement protein (TMV-MP) has pleiotropic effects
when expressed in transgenic tobacco (Nicotiana tabacum) plants. In
addition to its ability to increase the plasmodesmal size-exclusion limit,
the TMV-MP alters carbohydrate metabolism in source leaves and dry matter
partitioning between the various plant organs. In the present study the
TMV-MP was expressed under the control of a phloem-specific promoter
(rolC), and this system was employed to further explore the potential sites
at which the TMV-MP exerts its influence over carbon metabolism and
transport in transgenic potato (Solanum tuberosum) plants.
Immunohistochemical analyses indicated that the TMV-MP was localized mainly
to phloem parenchyma and companion cells. Starch and sucrose accumulated in
source leaves of these plants to significantly higher levels compared with
control potato lines. In addition, the rate of sucrose efflux from excised
petioles was lower compared with control plants. Furthermore, under
short-day conditions, carbon partitioning was lower to the roots and higher
to tubers in rolC plants compared with controls. These results are
discussed in terms of the mode(s) by which the TMV-MP exerts its influence
over carbon metabolism and photoassimilate translocation.