Plant glucose transporter structure and function
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INVITED REVIEW
Plant glucose transporter structure and function Dietmar Geiger 1 Received: 11 July 2020 / Revised: 6 August 2020 / Accepted: 10 August 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The carbohydrate D-glucose is the main source of energy in living organisms. In contrast to animals, as well as most fungi, bacteria, and archaea, plants are capable to synthesize a surplus of sugars characterizing them as autothrophic organisms. Thus, plants are de facto the source of all food on earth, either directly or indirectly via feed to livestock. Glucose is stored as polymeric glucan, in animals as glycogen and in plants as starch. Despite serving a general source for metabolic energy and energy storage, glucose is the main building block for cellulose synthesis and represents the metabolic starting point of carboxylate- and amino acid synthesis. Finally yet importantly, glucose functions as signalling molecule conveying the plant metabolic status for adjustment of growth, development, and survival. Therefore, cell-to-cell and long-distance transport of photoassimilates/ sugars throughout the plant body require the fine-tuned activity of sugar transporters facilitating the transport across membranes. The functional plant counterparts of the animal sodium/glucose transporters (SGLTs) are represented by the proton-coupled sugar transport proteins (STPs) of the plant monosaccharide transporter(-like) family (MST). In the framework of this special issue on “Glucose Transporters in Health and Disease,” this review gives an overview of the function and structure of plant STPs in comparison to the respective knowledge obtained with the animal Na+-coupled glucose transporters (SGLTs). Keywords STP . Sugar transport protein . Glucose transport . Plant photoassimilate partitioning
Introduction Larger body size and an increase in complexity is a major trend in animal and plant evolution. Unicellular and multicellular organisms depend on diffusion to supply gases (oxygen, carbon dioxide) and nutrients as well as to remove toxic compounds. However, diffusion represents a slow process and works only across small distances (< 1 mm; [70]). With the appearance of organisms with a larger body size, the surface area cannot meet the needs of its volume in terms of nutrient and gas supply [34, 92]. To deliver essential substances to and from each cell in the body, the need arose to evolve internal transport systems to provide bulk flow transport. In both, higher plants and animals, long-distance transport of carbohydrates is realized by a system of specialized tubes. This article is published as part of the Special Issue on “Glucose Transporters in Health and Disease” * Dietmar Geiger [email protected] 1
Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs-Institute, Biocenter, University of Wuerzburg, 97082 Wuerzburg, Germany
In vertebrates, the vasculature forms a circulatory system of arteries, capillaries, and veins. In the closed circulatory system of vertebrat
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