Hydrodynamic radius alone governs the mobility of molecules through plasmodesmata

Abstract

Various fluorescent molecular probes have been injected into the cytoplasm of nectary trichome cells of Abutilon striatum to ascertain the conductivity of the plasmodesmata. Most of the probes were based on fluorescein conjugated to a range of amino acids and peptides. The probes are not broken down by cytoplasmic enzymes during the period of observation. The results indicate that there are no specific effects of aromatic amino acids, either polar or hydrophobic types, on the conductivity of the Abutilon plasmodesmata, contrary to reports for other plants. The conductivity of the plasmodesmata in the trichomes is slightly greater than for any that have been studied in the tissues of other plants. It is proposed that in Abutilon the mobility of a probe is determined solely by the effective Stokes radius of the molecule, and that the radius of the molecule is governed by the molecular weight and, in particular, by the nature of the side groups in the peptide chain attached to the fluorochrome. Calculations are presented which indicate that channels between material in the plasmodesmatal annulus are the most likely route for the diffusion of the probes, and that the width of individual channels in the annulus is close to 3 nm.

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

“…Plasmodesmatal pores may be capable of further constriction under some circumstances (Robards and Lucas, 1990). This ultrastructure is thought to divide the cytoplasmic annulus of the plasmodesmata into a series of channels 2 to 3 nm in diameter (Terry and Robards, 1987), in contrast to the pore diameter of 50 to 100 nm assumed by Tyree (1970).…”

“…However, recent work on plasmodesmatal ultrastructure (Overall et al, 1982; Ding et al, 1992) and on symplasmic transport using fluorescently labeled tracers of different sizes Goodwin, 1983, 1985; Terry and Robards, 1987) suggests that the transport capacity of plasmodesmata is significantly less than was previously believed. In addition, these previous models did not account for the transport demands imposed by growth in a multicellular organ.…”

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

“…Indeed, Wolf et al (1989) reported movement of a 3"9K dye in 14% of injections (one of seven injections) into tobacco mesophyll cells; they nevertheless considered this figure negligible. Terry & Robards (1987) showed that a 1.1K F-dextran probe could move symplastically in nectary trichome cells ofAbutilon striatum, in more than 70 % of the cases. The conductivity of plasmodesmata was proposed to be slightly greater than for the other higher plants.…”

Development and function of plasmodesmata in zygotes of Fucus distichus

“…The SEL in land plants is 1-3 kDa (Erwee and Goodwin 1983, Goodwin 1983, Terry and Robards 1987, Kempers et al 1993, Radford and White 2001. Genetic analysis of plasmodesmata showed that a high occurrence of branched plasmodesmata is related to the ability for transportation of larger molecules compared with the wild type (Kim et al 2002, Burch-Smith and Zambryski 2010.…”

“…The size exclusion limit (SEL), which has been measured by microinjection of fluorescent tracers with different sizes is 1-3 kDa, depends on the species and cell types (Erwee and Goodwin 1983, Goodwin 1983, Terry and Robards 1987, Kempers et al 1993, Radford and White 2001. Molecular movement and SEL in plasmodesmata are regulated by a divalent ion such as Ca 2+ (Erwee and Goodwin 1983) and by degeneration/ synthesis of callose deposited at the constricted neck region of the plasmodesmata (Radford and White 2001, Zavaliev et al 2011.…”