Intracellular and intercellular compartmentation of carbohydrate metabolism in leaves of temperate gramineae

Abstract

-This review considers the importance of compartmentation in the regulation of carbohydrate metabolism in leaves. We draw particular attention to the role of the vacuole as a site for storage of soluble sugars based on sucrose, and discuss briefly their characteristic metabolism. We also point out inconsistencies between the observed properties of vacuoles and the behaviour in vitro of the enzymes of fructan biosynthesis that do not support the hypothesis that the vacuole is the site of synthesis as well as of storage. We also consider compartmentation of carbohydrate metabolism between different cell types, using mainly our studies on leaves of temperate C3 gramineae. Here we present evidence of significant differences in carbon metabolism between epidermis, mesophyll, bundle sheath and vasculature based upon both single-cell sampling and immunolocalisation. The implications of these differences for the control of metabolism in leaves are discussed.RESUMO -(Compartimentação intracelular e intercelular do metabolismo de carboidratos em folhas de gramíneas de regiões temperadas). Esta revisão considera a importância da compartimentação para a regulação do metabolismo de carboidratos nas folhas, com destaque especial para o papel do vacúolo como local de armazenamento de carboidratos solúveis derivados da sacarose e seu característico metabolismo. Inconsistências entre as propriedades dos vacúolos e o comportamento in vitro das enzimas de biossíntese de frutanos são também destacadas, uma vez que não dão suporte à hipótese de que o vacúolo, é o local de síntese e armazenamento desses compostos. A compartimentação do metabolismo de carboidratos em diferentes tipos de células também é considerada em folhas de gramíneas C3 de regiões temperadas. Através de estudos com células isoladas e de imunolocalização são apresentadas evidências de diferenças significativas entre o metabolismo de carbono em epiderme, mesófilo, bainha de feixes e tecidos vasculares; são discutidas as implicações dessas diferenças no controle do metabolismo foliar.

A Novel Arabidopsis Vacuolar Glucose Exporter Is Involved in Cellular Sugar Homeostasis and Affects the Composition of Seed Storage Compounds

“…In support of this aspect, several studies have provided biochemical evidence for the uptake of both Suc and hexoses into vacuoles (Thom et al, 1982;Rausch, 1991;Keller, 1992), and both passive diffusion and active transport have been determined as uptake mechanisms for these sugars (Thom and Komor, 1984;Martinoia et al, 1987Martinoia et al, , 2000. Furthermore, determination of subcellular sugar concentrations in a variety of plants via nonaqueous fractionation (Gerhardt and Heldt, 1984) revealed that in leaves, Glc is predominantly found in the vacuole, while Suc is mainly found in the cytosol or is evenly distributed (Wagner, 1979;Heineke et al, 1994;Pollock et al, 2000;Voitsekhovskaja et al, 2006).…”

The monosaccharide transporter(‐like) gene family in Arabidopsis

“…The application of a non‐aqueous fractionation technique allowed estimates of the relative amounts of sugars in sub‐cellular compartments. Measurements of sugar concentrations in a variety of plants revealed that in leaves the vast majority of glucose is found in the vacuole [12–17] (Lohaus G., personal communication).…”

Expression analysis and functional characterization of the monosaccharide transporters, OsTMTs, involving vacuolar sugar transport in rice (Oryza sativa)

“…Vacuoles serve as a main long-term and also temporary storage pool in the cell (i.e. metabolites produced in excess are transported into vacuoles and released according to metabolic requirements; Cairns et al, 2000;Pollock et al, 2000;Wormit et al, 2006;Martinoia et al, 2007;Neuhaus, 2007). In this process, specific tonoplast sugar transporters are required for the vacuolar transport of these nutrients.…”

“…metabolites produced in excess are transported into vacuoles and released according to metabolic requirements; Cairns et al. , 2000; Pollock et al. , 2000; Wormit et al.…”