PHLOEM-SPECIFIC EXPRESSION OF THE TOBACCO MOSAIC-VIRUS MOVEMENT PROTEIN ALTERS CARBON METABOLISM AND PARTITIONING IN TRANSGENIC POTATO PLANTS

The tobacco mosaic virus movement protein (TMV-MP) has pleiotropic eff ects when expressed in transgenic tobacco (Nicotiana tabacum) plants. In addition to its ability to increase the plasmo-desmal size-exclusio n limit, the TMV-MP alters carbohydrate metabolism in source leaves an d dry matter partitioning between the various plant organs. In the pre sent study the TMV-MP was expressed under the control of a phloem-spec ific promoter (rolC), and this system was employed to further explore the potential sites at which the TMV-MP exerts its influence over carb on metabolism and transport in transgenic potato (Solanum tuberosum) p lants. Immunohistochemical analyses indicated that the TMV-MP was loca lized mainly to phloem parenchyma and companion cells. Starch and sucr ose accumulated in source leaves of these plants to significantly high er 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 w as lower to the roots and higher to tubers in rolC plants compared wit h controls. These results are discussed in terms of the models) by whi ch the TMV-MP exerts its influence over carbon metabolism and photoass imilate translocation.