EFFECT OF THE ALFALFA MOSAIC-VIRUS MOVEMENT PROTEIN EXPRESSED IN TRANSGENIC PLANTS ON THE PERMEABILITY OF PLASMODESMATA

Symplastic transport of different sized fluorescent probes has been as sessed in leaf epidermal cells of transgenic Nicotiana plants expressi ng the movement protein (MP) of alfalfa mosaic virus (AMV). In both N. tabacum and N. benthamiana, the size exclusion limit (SEL) of plasmod esmata increased from M(r) 1000, which represents the commonly accepte d limit, to over 4-4K. However, in control plants, movement of a 3K pr obe was seen in 11 to 22 % of the injections, indicating that plasmode smata may on occasion allow the passage of molecules larger than was p reviously thought. The increase of SEL due to the presence of the AMV MP, although significant, remains insufficient to permit the passage o f viral particles and the possibility of other mechanisms involved in viral cell-to-cell spread is discussed.