Acetaldehyde Stimulation of Net Gluconeogenic Carbon Movement from Applied Malic Acid in Tomato Fruit Pericarp Tissue

Abstract

Applied acetaldehyde is known to lead to sugar accumulation in fruit including tomatoes (Lycopersicon esculentum) (O Paz, HW Janes, BA Prevost, C Frenkel [1982] presumably due to stimulation of gluconeogenesis. This conjecture was examined using tomato fruit pencarp discs as a test system and applied -[U-14C]malic acid as the source for gluconeogenic carbon mobilization. The label from malate was recovered in respiratory C02, in other organic acids, in ethanol insoluble material, and an appreciable amount in the ethanol soluble sugar fraction. In Rutgers tomatoes, the label recovery in the sugar fraction and an attendant label reduction in the organic acids fraction intensified with fruit ripening. In both Rutgers and in the nonripening tomato rin, these processes were markedly stimulated by 4000 ppm acetaldehyde. The onset of label apportioning from malic acids to sugars coincided with decreased levels of fructose-2,6-biphosphate, the gluconeogenesis inhibitor.In acetaldehyde-treated tissues, with enhanced label mobilization, this decline reached one-half to one third of the initial fructose-2,6-biphosphate levels. Application of 30 micromolar fructose-2,6-biphosphate or 2,5-anhydro-d-mannitol in tum led to a precipitous reduction in the label flow to sugars presumably due to inhibition of fructose-1,6-biphosphatase by the compounds. We conclude that malic and perhaps other organic acids are carbon sources for gluconeogenesis occurring normally in ripening tomatoes. The process is stimulated by acetaldehyde apparently by attenuating the fructose-2,6-biphosphate levels. The mode of the acetaldehyde regulation of fructose-2,6-biphosphate metabolism awaits clarification.AA4 is a common volatile in plants that accumulate during physiological disorders (25) and in ripening fruit (7,14).

Overexpression of the phosphoenolpyruvate carboxykinase gene (<i>SlPEPCK</i>) promotes soluble sugar accumulation in fruit and post-germination growth of tomato (<i>Solanum lycopersicum</i> L.)

“…These results indicate that the modified PEPCK level directly affects the sugar and organic acid contents, likely through gluconeogenesis. While it has been reported that the predominant metabolic flow in the flesh of tomato and grape is glycolysis (Carrari et al 2006;Famiani et al 2014), early labelling studies demonstrated that gluconeogenesis occurs during tomato fruit ripening (Farineau and Laval-Martin 1977;Halinska and Frenkel 1991). Our present results indicate that gluconeogenesis is involved in sugar accumulation in fruit, and PEPCK plays a regulatory role in this process.…”

Salinity Stress Affects Assimilate Metabolism at the Gene-expression Level during Fruit Development and Improves Fruit Quality in Tomato (Solanum lycopersicum L.)

“…Bahrami et al (2001) isolated the gene from tomato and showed that its expression increases during ripening. Although previous labeling studies have demonstrated that gluconeogenesis occurs in ripening tomato fruit (Farineau and Laval-Martin, 1977;Halinska and Frenkel, 1991), and cold-inducible PEPCK was reported in rapeseed (Sáez-Vásquez et al, 1995), its regulation in response to abiotic stress is not fully understood in plants. Our data suggest that salinity stress enhances gluconeogenesis, as well as metabolic flow in ripe fruit, resulting in high-Brix fruit.…”

Effect of Light Condition on Water and Carbon Balance in Satsuma Mandarin (Citrus unshiu Marc.) Fruit

“…In fruit development under such conditions, substantial restrictions in translocation from leaf to fruit, in carbon metabolism, and induction of gluconeogenesis from organic acid may occur; then, PEPC and PEPCK activities of fruit may play a key role for sugar accumulation and acid reduction. In grape, cherry, and tomato, there is evidence that gluconeogenesis from malate may occur (Halinska and Frenkel, 1991;Leegood and Walker, 1999).…”