Plasmodesmatal frequency in relation to short-distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast.

Botha, C.E.J. and Cross, R.H.M. (1997) Plasmodesmatal frequency in relation to short-distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast. Physiologia Plantarum, 99 (3). pp. 355-362. ISSN 003I-9317

[img]
Preview
Text
bundles.pdf

285Kb

Official URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb00547...

Abstract

We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin-walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin- and thick-walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore-plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell-sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles. The degree of cellular connectivity and the potential isolation of the companion cell-sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential {average -52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (-122.5 mV) recorded for the companion cell-thin-walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s-1) longitudinal and radial transport in the bundle sheath-vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell-sieve tube complex, did not demonstrate backward connectivity to the bundle sheath. We conclude that the low plasmodesmatal frequencies, coupled with a two-domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.

Item Type:Article
Additional Information:The definitive version is available at www.blackwell-synergy.com
Uncontrolled Keywords:Barley, dye-coupling, Hordeum vulgare, iontophoresis, plasmodesmatal frequency, phloem loading pathway, symplastic and apoplastic transport
Subjects:Y Unknown > Subjects to be assigned
Divisions:Support Units > Electron Microscope Unit
Faculty > Faculty of Science > Botany
ID Code:845
Deposited By: Ms Vivien Botha
Deposited On:15 Nov 2007
Last Modified:06 Jan 2012 16:19
277 full-text download(s) since 15 Nov 2007
87 full-text download(s) in the past 12 months
More statistics...

Repository Staff Only: item control page