Symplastic continuity in Agrobacterium tumefaciens induced tumours

The Agrobacterium tumefaciens-induced plant tumour is regarded as a strong sink, containing a well-developed vascular system that guarantees an effici ent supply of water and nutrients from the host plant into the tumour. The phloem transport and unloading of the fluorescent dye carboxyfluorescein (C F) was studied to examine the potential pathways for unloading of a low-mol ecular-mass solute, and was compared with the symplastic movement of potato virus X expressing a green fluorescent protein-coat protein fusion (PVX.GF P-CP). The distribution of both CF and PVX.GFP-CP in the host plant, Nicoti ana benthamiana, demonstrated a clear symplastic pathway between the phloem of the host stem and the cells of the tumour, and also a considerable capa city for subsequent cell-to-cell transport between tumour cells. This same pattern of CF transport was also demonstrated independently for the host sp ecies Cucurbita maxima and Ricinus communis. In addition to entering the tu mour, CF and PVX both moved through the vascular rays of the host stem towa rds the stele. The results confirm that host and tumour tissues in the Agro bacterium gall are in direct symplastic continuity and emphasize an importa nt symplastic pathway for radial solute transport in stems.