Protoplast hexose carrier activity is a determinate of genotypic difference in hexose storage in tomato fruit

Abstract

Post-phloem sugar transport in developing tomato (Lycopersicon esculentum Mill. cv. Flora-Dade) fruit follows an apoplastic route during the rapid phase of sugar accumulation. The pathway is characterized by sugar retrieval by the storage parenchyma cells from the fruit apoplast. Two tomato genotypes differing in fruit hexose content were compared in terms of the transport and transfer processes controlling fruit sugar levels. The genotypic difference in fruit sugar content was independent of photoassimilate export from source leaves. Discs of pericarp tissue were cultured in a medium based on analyses of the fruit apoplastic sap. The cultured discs maintained a composition, a relative growth rate and a respiration rate similar to those of the pericarp tissue of intact fruit. Estimates of hexose fluxes into metabolic and storage pools suggested that membrane transport regulated the genotypic difference in hexose accumulation. Short-term ['"^Clhexose uptake experiments demonstrated a genotypic difference in V^^^ for glucose, fructose and 3-O-methylglucose, and this difference was abolished in the presence of the inhibitor /7-chloromercuribenzenesulphonic acid (PCMBS). The results support the hypothesis that the activity of energized hexose carriers on the plasma membranes of storage parenchyma cells is a signiflcant determinate of the genotypic difference in hexose accumulation.

Sucrose deficiency delays lycopene accumulation in tomato fruit pericarp discs

“…At that time most of the work concerning the role of sucrose in tomato fruits using the whole plant has focused on fruit development and carbon metabolism demonstrating that sucrose affects fruit set (D'Aoust et al 1999), fruit growth (Hakel et al 2006) and starch metabolism (Nguyen-Quoc and Foyer 2001). As an alternative, in vitro culture of pericarp discs provides an efficient way to study tomato fruit ripening (Ruan et al 1997;Kuntz et al 1998;Campbell et al 1990;Sozzi et al 2002;Vardhini and Rao 2002). In the present study, fruit pericarp discs prepared from mature green fruits were incubated in vitro in a liquid medium in order to limit gas diffusion, prevent tissue dehydration and insure an efficient intake of metabolites.…”

Dynamic Analysis of Growth, Water Balance and Sap Fluxes through Phloem and Xylem in a Tomato Fruit: Short-term Effect of Water Stress

“…This sugar transport across the plasma membranes depends on hexose/proton symport driven by H+-ATPase on the membranes (Rausch, 1991;Fisher and Oparka, 1996;Patrick and Offler, 1996). Ruan et al (1997) have demonstrated in vitro that activity of the hexose/proton symport across the membranes can be a determinant for sugar accumulation in the storage pericarp cells under sufficient supply of hexose. Kitano et al (1998b) also confirmed this energy-dependent sugar accumulation in intact fruit where rates of fruit growth and sugar translocation during the light period depended on fruit respiration, and were completely retarded by inhibiting fruit respiration.…”

“…Furthermore, fruit respiration can affect post-phloem transport in the fruit, i.e. sugar transport from unloading sites to storage cells of pericarp tissues (Ruan and Patrick, 1995;Ruan et al, 1997). Therefore, simultaneous measurement of dynamics of expansive growth, water balance, phloem sap and xylem sap fluxes, transpiration and respiration in intact tomato fruits is essential for quantitative analyses of environmental effects on mass accumulation in the fruits.…”

Genome-wide identification, phylogeny, and expression analysis of the SWEET gene family in tomato

“…While the role of these transporters in sucrose loading into the phloem has been identified, less is known about how export toward ripening fruits is facilitated. The uptake of hexoses from the fruit apoplast to the storage parenchyma cells is thought to be achieved by the hexose transporters LeHT1 and LeHT3 (Ruan et al, 1997;Dibley et al, 2005;McCurdy et al, 2010). A number of metabolomics studies on the ripening of tomato fruit have revealed dynamic patterns of accumulation (Roessner-Tunali et al, 2003;Carrari and Fernie, 2006;Schauer et al, 2006;Carrari et al, 2007;Luengwilai et al, 2010).…”