Sugar Selectivity and Other Characteristics of Phloem Loading in Beta vulgaris L. 12
AUTOR(ES)
Fondy, Bernadette R.
RESUMO
The rate of phloem loading, its selectivity, and the disposition of labeled carbon were studied following application of 14C-labeled sugars to the free space of source leaves of sugar beet (Beta vulgaris L.). Buffered 10 mm solutions of 14C-labeled sucrose, fructose, stachyose, mannitol, 3-0-methyl glucose or l-glucose were applied to the abraded epidermis of source leaves held in the dark. Distribution of the labeled carbon from sugar taken up from the free space was studied by micro-densitometry of autoradiographs. Uptake of labeled sugar from the free space, partition between mesophyll and minor veins, metabolic conversions, export and respiration were followed during the 3-hr time course studies. Rates of sugar uptake into the minor veins, flux rates through the sieve element-companion cell complex membrane and concentration ratios between free space and the interior of the minor vein phloem cells were compared for the six sugars studied for evidence of active uptake. The composition of the free space solution in leaves photosynthesizing in 14CO2 was studied by vacuum infiltration of the source leaf air spaces and removal of the solution by centrifugation. Labeled compounds in this solution were compared to those in an aqueous ethanol extract of the same leaf pieces.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=543334Documentos Relacionados
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