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Felix Keller - One of the best experts on this subject based on the ideXlab platform.

  • Carbohydrate Transport in discs of storage parenchyma of celery petioles 2 uptake of mannitol
    New Phytologist, 1991
    Co-Authors: Felix Keller
    Abstract:

    Preliminary experiments had suggested the existence of an active mannitol carrier in discs isolated from celery petiole parenchyma. I now report in more detail on mannitol uptake into these discs

  • Carbohydrate Transport in discs of storage parenchyma of celery petioles
    New Phytologist, 1991
    Co-Authors: Beate Diettrich, Felix Keller
    Abstract:

    summary Petioles of celery leaves function successively as net importing (sink) and net exporting (source) organs during ontogeny. The parenchyma of these petioles is the main store for large amounts of D-glucose, D-fructose and mannitol. The mechanism of uptake of glucose and fructose into discs isolated from storage parenchyma of celery petioles was investigated. Uptake kinetics showed a biphasic response to increasing concentrations for both hexoses with a saturable component at low concentrations and a non-saturable, linear, diffusion-like component at higher concentrations (at least up to 16 mM). The apparent Kns-values were an order of magnitude higher for fructose (2–3 mM) than for glucose (034 RIM) uptake. The saturable components of uptake of the two hexoses were inhibited similarly by the SH-reagents PCMBS and NEM, the uncouplers CCCP and DNP, the ATPase inhibitor DES and the hydrophobic reagents phloretin and phlorizin. They were stimulated by the plasmalemma H+-ATPase stimulator FC and showed a broad pH-optimum around pH 6. Competition studies revealed that glucose uptake was very specific whereas fructose uptake was inhibited by D-glucose, L-sorbose and D-tagatose. The saturable components of uptake of both hexoses were clearly turgor-dependent. Lowering of cell turgor resulted in a linear increase of Vmax and a constant Km. It is concluded that the saturable components of glucose and fructose uptake are of a similar, active, sugar-proton coTransport type with carriers containing SH-groups and interacting hydrophobically. It is suggested that two different hexose carriers might be operative, one for glucose only and one for both glucose and fructose.

Zhijun Cheng - One of the best experts on this subject based on the ideXlab platform.

Francesca Turroni - One of the best experts on this subject based on the ideXlab platform.

Xiaohui Li - One of the best experts on this subject based on the ideXlab platform.

Michele N Holbrook - One of the best experts on this subject based on the ideXlab platform.

  • maintenance of Carbohydrate Transport in tall trees
    Nature plants, 2017
    Co-Authors: Jessica A Savage, Sierra D Beecher, Laura E Clerx, Jessica T Gersony, Jan Knoblauch, Juan M Losada, Kaare Hartvig Jensen, Michael Knoblauch, Michele N Holbrook
    Abstract:

    Trees present a critical challenge to long-distance Transport because as a tree grows in height and the Transport pathway increases in length, the hydraulic resistance of the vascular tissue should increase. This has led many to question whether trees can rely on a passive Transport mechanism to move Carbohydrates from their leaves to their roots. Although species that actively load sugars into their phloem, such as vines and herbs, can increase the driving force for Transport as they elongate, it is possible that many trees cannot generate high turgor pressures because they do not use Transporters to load sugar into the phloem. Here, we examine how trees can maintain efficient Carbohydrate Transport as they grow taller by analysing sieve tube anatomy, including sieve plate geometry, using recently developed preparation and imaging techniques, and by measuring the turgor pressures in the leaves of a tall tree in situ. Across nine deciduous species, we find that hydraulic resistance in the phloem scales inversely with plant height because of a shift in sieve element structure along the length of individual trees. This scaling relationship seems robust across multiple species despite large differences in plate anatomy. The importance of this scaling becomes clear when phloem Transport is modelled using turgor pressures measured in the leaves of a mature red oak tree. These pressures are of sufficient magnitude to drive phloem Transport only in concert with structural changes in the phloem that reduce Transport resistance. As a result, the key to the long-standing mystery of how trees maintain phloem Transport as they increase in size lies in the structure of the phloem and its ability to change hydraulic properties with plant height. The phloem is the system of ‘blood vessels’ that translocates Carbohydrates from the leaves to different plant organs. Here, using new structural imaging and pressure measuring tools, the researchers show interesting phloem structural changes that ensure a passive Transport mechanism in tall trees.