Secondary plasmodesmata are specific sites of localization of the tobacco mosaic virus movement protein in transgenic tobacco plants.

Abstract

Expresslon of the tobacco mosalc virus 30-kD movement protein (TMV MP) gene in tobacco plants increases the plasmodesmatal size exclusion limlt (SEL) 10-fold between mesophyll cells in mature leaves. In the present study, we examined the structure of plasmodesmata as a functlon of leaf development. In young leaves of 30-kD TMV MP transgenic (line 274) and vector control ( l h e 306) plants, almost all plasmodesmata were primary in nature. In both plant lines, secondary plasmodesmata were formed, in a basipetal pattern, as the leaves underwent expansion growth. Ultrastructural and immunolabellng studies demonstrated that ln line 274 the TMV MP accumulated predominantly in secondary plasmodesmata of nonvascular tissues and was associated with a filamentous material. A developmental progression was detected in terms of the presence of TMV MP; all secondary plasmodesmata in the tip of the fourth leaf contained TMV MP in association with the filamentous material. Dye-coupling experiments demonstrated that the TMV MP-induced increase in plasmodesmatal SEL could be routinely detected in the tip of the fourth leaf, but was restricted to mesophyll and bundle sheath cells. These findings are dlscussed with respect to the structure and function of plasmodesmata, particularly those aspects related to virus movement.

Expression of a luteoviral movement protein in transgenic plants leads to carbohydrate accumulation and reduced photosynthetic capacity in source leaves

“…These results differ from those obtained with transgenic tobacco plants expressing MP30. In the latter only secondary plasmodesmata and primarily those between mesophyll but rarely between vascular cells were altered (Ding et aL, 1992). The aberrant structure of plasmodesmata only in the phloem tissue of young transgenic plants may suggest that the initial impact of MP17 on limited sucrose loading results from irregular or inhibited macromolecular trafficking between cells of the vascular tissue of molecules essential for loading.…”

Effect of the alfalfa mosaic virus movement protein expressed in transgenic plants on the permeability of plasmodesmata

“…The AMV MP alters the plasmodesmal permeability increasing the SEL to over 4.4K, thus causing a modification functionally equivalent to that observed after trichome cell infection with tobacco rattle virus (Derrick et al, 1992). Nevertheless, this represents a relatively minor functional alteration in comparison to that induced by the TMV MP, which enables the passage of 10K probes in non-vascular tissue (Ding et al, 1992). One has to take into account, however, that in the latter work, the designation 'nonvascular tissue' did not include the epidermis for which no specific data were presented.…”

Ultrastructural study of plasmodesmata in the brown alga Dictyota dichotoma (Dictyotales, Phaeophyceae)

“…In green plants, many ultrastructural studies on PD have been published, using TEM (Robards 1968, Fraster and Gunning 1969, Kwiatkowska and Maszewski 1986, Ding et al 1992a, b, Botha et al 1993, Franceschi et al 1994, Volk et al 1996, Cook et al 1997. The most characteristic structural feature of PD in land plants is that they have appressed ER called desmotubule (Robards and Lucas 1990).…”