Evidence for Symplastic Phloem Unloading in Sink Leaves of Barley1
The pathway of phloem unloading in sink barley ( Hordeum vulgare ) leaves was studied using a combination of electron microscopy, carboxyfluorescein transport, and systemic movement of barley stripe mosaic virus expressing the green fluorescent protein. Studies of plasmodesmatal frequencies between...
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Veröffentlicht in: | Plant physiology (Bethesda) 2001-01, Vol.125 (1), p.209-218 |
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Sprache: | eng |
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Zusammenfassung: | The pathway of phloem unloading in sink barley (
Hordeum
vulgare
) leaves was studied using a combination of electron
microscopy, carboxyfluorescein transport, and systemic movement of
barley stripe mosaic virus expressing the green fluorescent protein.
Studies of plasmodesmatal frequencies between the phloem and mesophyll
indicated a symplastic sieve element- (SE) unloading pathway involving
thick-walled and thin-walled SEs. Phloem-translocated
carboxyfluorescein was unloaded rapidly from major longitudinal veins
and entered the mesophyll cells of sink leaves. Unloading was
“patchy” along the length of a vein, indicating that sieve element
unloading may be discontinuous along a single vascular bundle. This
pattern was mirrored precisely by the unloading of barley stripe mosaic
virus expressing the green fluorescent protein. Transverse veins were
not utilized in the unloading process. The data collectively indicate a
symplastic mechanism of SE unloading in the sink barley leaf. |
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ISSN: | 0032-0889 1532-2548 |