Sucrose-to-Starch Metabolism in Tomato Fruit Undergoing Transient Starch Accumulation

Abstract

lmmature green tomato (Lycopersicon esculenfum) fruits undergo a period of transient starch accumulation characterized by developmental changes in the activities of key enzymes in the sucrose (Suc)-to-starch metabolic pathway. Activities of Suc synthase, fructokinase, ADP-glucose (Clc) pyrophosphorylase, and soluble and insoluble starch synthases decline dramatically in parallel to the decrease i n starch levels in the developing fruit. Comparison of "maximal" i n vitro activities of the enzymes in the Suc-to-starch pathway suggests that these same enzymes are limiting to the rate of starch accumulation. In contrast, activities of invertase, UDP-Clc pyrophosphorylase, nucleoside diphosphate kinase, phosphoglucoisomerase, and phosphoglucomutase do not exhibit dramatic decreases in activity and appear to be in excess of starch accumulation rates. Starch accumulation is spatially localized in the inner and radial pericarp and columella, whereas the outer pericarp and seed locule contain little starch. The seed locule is characterized by lower activities of Suc synthase, UDP-Clc pyrophosphorylase, phosphoglucomutase, ADP-Clc pyrophosphorylase, and soluble and insoluble starch synthases. The outer pericarp exhibits comparatively lower activities of ADP-Clc pyrophosphorylase and insoluble starch synthase only. These data are discussed in terms of the developmental and tissue-specific coordinated control of Suc-to-starch metabolism.

Comprehensive Tissue-Specific Transcriptome Analysis Reveals Distinct Regulatory Programs during Early Tomato Fruit Development

“…4B). This is consistent with starch being a major storage form of fixed carbon (Schaffer and Petreikov, 1997) and with previous reports of continual starch synthesis and degradation in growing fruit (NguyenQuoc and Foyer, 2001). .…”

Changes in Transcriptional Profiles Are Associated with Early Fruit Tissue Specialization in Tomato

“…Many of these genes (up to 36% in the locular tissue) encode proteins with unknown functions or, alternatively, present no homology with known genes. Our findings correlate well for the few genes or enzymatic activities previously studied in the developing fruit (Laval-Martin et al, 1977;Schaffer and Petreikov, 1997;Rebers et al, 1999;RodriguezConception and Gruissem, 1999;Joubès et al, 2000;Lemaire-Chamley et al, 2000;Muir et al, 2001;Guillet et al, 2002;Busi et al, 2003;Obiadalla-ali et al, 2004). Interestingly, the repartition of the known genes into the different functional categories is very different between the exocarp and the locular tissue.…”

“…Since most of the studies to date have focused on the entire fruit or on the carpel wall, how the different fruit tissues contribute to fruit growth and affect fruit quality remains poorly understood. There are nevertheless some indications of early tissue specialization in the fruit, since structural and biochemical changes such as cell size (Mohr and Stein, 1969;Gillaspy et al, 1993), endoreduplication level (Joubès et al, 1999), photosynthesis (Laval-Martin et al, 1977;Meier et al, 1995), starch accumulation (Schaffer and Petreikov, 1997), cell wall polysaccharides (Cheng and Huber, 1996), and flavonoid composition (Muir et al, 2001) show great variation among the different fruit tissues. These data suggest coordinated expressions of genes with specific roles in the control of growth and regional differentiation in the various tissues of the developing fruit.…”

SlARF4, an Auxin Response Factor Involved in the Control of Sugar Metabolism during Tomato Fruit Development

“…Starch biosynthesis is known to involve a series of enzyme-catalyzed processes (Smith, 1999;Liang et al, 2001;James et al, 2003) belonging to three separate enzyme families (Fig. 5), AGPase, STS, and SBE (Yelle et al, 1988;Schaffer and Petreikov, 1997). Building on the annotated tomato genome sequence, genome-wide in silico screening allowed for the identification of all members of the three enzyme families involved in starch synthesis in tomato.…”

“…During this stage, starch, which represents the major carbon reserve in the fruit, reaches a maximal accumulation (Ho, 1996). The second stage corresponds to cell enlargement associated with the degradation of starch into soluble sugars (Davies and Cocking, 1965;Schaffer and Petreikov, 1997). The last stage corresponds to a slow growth phase comprising the fruit-ripening phase, characterized by intensive metabolic changes that lead to Glc and Fru accumulation .…”