Sucrose transport from source to sink seeds in rice

Abstract

In many higher plants, sucrose is loaded as a major carbon photoassimiliate into the phloem apoplastically by sucrose transporters (SUTs) and unloaded in sink tissues, where it serves as a storage material, carbohydrate backbone, and energy source. In sink tissues, a proportion of sucrose molecules are converted by cell wall invertases (CINs) into hexose that is imported into cells by monosaccharide transporters (MSTs). Thus, in developing seeds, co‐ordinated regulation of SUTs, CINs, and MSTs is crucial in carbon distribution. Here, we summarize current efforts on the identification of SUTs, CINs, and MSTs in rice.

Structure, expression, and functional analysis of the hexokinase gene family in rice (Oryza sativa L.)

“…Previously, high levels of invertase activity and a high hexose-to-sucrose ratio were found in young cereal seeds, including maize (Cheng and Chourey 1999), rice (Hirose et al 2002), and barley (Borisjuk et al 2004). Notably, in developing seeds, the shift from cell division to storage product accumulation is coincident with the change from invertase to sucrose synthasemediated sucrose metabolism and from high hexose-tosucrose to high sucrose-to-hexose (Borisjuk et al 2004;Koch 2004;Lim et al 2006). Thus, our observations suggest that OsHXKs, except for OsHXK8, play a role in early embryo and endosperm development during the longitudinal growth of rice seeds.…”

“…3a). Sucrose is unloaded in the sink rice seeds where it serves as a storage material, carbohydrate backbone, and energy source (Borisjuk et al 2004;Lim et al 2006). Since hexokinases are thought to play an important role in utilizing hexoses produced from sucrose hydrolysis during seed development (Koch 2004), the eight genes, OsHXK2 through OsHXK9, expressed in immature seeds were analyzed further.…”

Impaired Function of the Tonoplast-Localized Sucrose Transporter in Rice, OsSUT2, Limits the Transport of Vacuolar Reserve Sucrose and Affects Plant Growth

“…Seeds are elongated longitudinally with the cellularization and proliferation of endosperm cells during the prestorage phase (1-6 d after fertilization [DAF]) and thickened during the starch-filling milky phase (7-15 DAF) in rice (Hirose et al, 2002;Lim et al, 2006). In developing immature seeds of transgenic pOsSUT2:: GUS lines, high GUS activity was observed in the 7-to 8-DAF seed coat at the early starch-filling stage, while only low activity was observed at 3 to 4 DAF in the prestorage phase seed (Fig.…”

“…Suc transport occurs at both the whole plant and intracellular levels, and this sugar is loaded over a short distance to the phloem either apoplastically by the plasma membrane sucrose transporters (SUTs) or symplastically through plasmodesmata, depending on the plant species (Rennie and Turgeon, 2009). Subsequent to phloem loading, Suc is transported over a long distance to sink tissues (ap Rees and Hill, 1994;Williams et al, 2000;Lalonde et al, 2004;Lim et al, 2006;Sauer, 2007). Within cells, Suc is partitioned into organelles, especially vacuoles, for short-term or long-term storage.…”

“…The orchestrated production, transport, and storage of Suc, therefore, is essential for normal plant growth and development (Lalonde et al, 2004;Lim et al, 2006;Kü hn and Grof, 2010). Suc transport occurs at both the whole plant and intracellular levels, and this sugar is loaded over a short distance to the phloem either apoplastically by the plasma membrane sucrose transporters (SUTs) or symplastically through plasmodesmata, depending on the plant species (Rennie and Turgeon, 2009).…”