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Changes in metabolites were studied during the fruit development of two greenhouse grown peach [Prunus persica (L.) Batsch] cultivars with low acidity (`Jalousia') or normal acidity (`Fantasia'). Both cultivars had the same sucrose concentration in fruit mesocarp at maturity. In the fruit juice, pH was higher and titratable acidity was lower for `Jalousia' than for `Fantasia' from 80 days after bloom to maturity. At four different times during fruit development, in vivo 13C NMR spectroscopy was used to measure the vacuolar pH of fruit mesocarp. At 55 days after bloom, the vacuolar pH of fruit mesocarp was not significantly different between `Jalousia' and `Fantasia', whereas the juice pH was different between cultivars. The three major organic acids in fruit mesocarp were malic, citric, and quinic acids for both cultivars. Citric acid concentrations were similar in both cultivars until ≈85 days after bloom and then became significantly higher in `Fantasia'. A significantly higher concentration in malic acid in `Fantasia' than in `Jalousia' was observed from the end of the first growth phase to maturity. At maturity, `Fantasia' fruit had two and five times more malic and citric acid, respectively, than `Jalousia' fruit. The differences observed between `Jalousia' and `Fantasia' fruit for malic and citric acid concentrations accounted for the difference in titratable acidity. The differences in acid concentration appeared during the plateau between the two rapid growth phases of the fruit, i.e., far before the onset of maturation. The three major amino acids were asparagine, glutamic acid, and proline for both cultivars. Their concentration followed similar patterns in acid and low-acid fruit.

Sorbitol and sucrose are the two main soluble carbohydrates in mature peach leaves. Both are translocated in the phloem, in peach as in other rosaceous trees. The respective role of these two soluble carbohydrates in the leaf carbon budget, and their phloem loading pathway, remain poorly documented. Though many studies have been carried out on the compartmentation and export of sucrose in sucrose-transporting species, far less is known about sorbitol in species transporting both sucrose and sorbitol. Sorbitol and sucrose concentrations were measured in several tissues and in sap, in 2-month-old peach (Prunus persica L. Batsch) seedlings, i.e. leaf blade, leaf main vein, petiole, xylem sap collected using a pressure bomb, and phloem sap collected by aphid stylets. The sorbitol to sucrose molar ratio depended on the tissue or sap, the highest value (about 7) found in the leaf main vein. Sorbitol concentration in the phloem sap was about 560 mM, whereas that of sucrose was about 140 mM. The lowest sorbitol and sucrose concentrations were observed in xylem sap collected from the shoot. The volume of the leaf apoplast, estimated by infiltration with ^H-inulin, represented about 17% ofthe leaf blade water content. This volume was used to calculate a global intracellular concentration for each carbohydrate in the leaf blade. Following these simplifying assumptions, the calculated concentration gradient between the leaf's intracellular compartment and phloem sap is nil for sorbitol and could thus allow for the sympiastic loading of the phloem of this alditol. However, infiltration of ''^C-labelled source leaves with 2 mM p-chloromercuribenzenesulfonic acid (PC-MBS), a potent inhibitor of the sucrose carrier responsible for phloem loading in sucrose-transporting plants, had a significant effect on the exudation of both labelled sucrose and sorbitol from the phloem. Therefore, in peach, which is a putative sympiastic loader according to minor vein anatomy and sorbitol concentration gradients, apoplastic loading may predominate.

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The synthesis of organic acids was studied during fruit devel-23 and 108 DAB in Fantasia. In Jalousia, they were very low at 23 DAB and reached levels similar to Fantasia at 108 opment of two peach (Prunus persica L. Batsch) cultivars, DAB. For both cultivars, in vitro PEPC activity expressed on Fantasia and Jalousia, having fruits with high and low organic a dry weight basis was maximal at 24 DAB, decreased from acid content, respectively. The malate content was higher in 24 to 60 DAB, and then remained constant. The activity of cv. Fantasia than in cv. Jalousia at the end of the first rapid growth stage (50 days after bloom [DAB]). Malate and citrate peach fruit PEPC appeared extremely sensitive to malate (I 0.5 of 100 mM for Fantasia and 65 mM for Jalousia at pH 7.3) contents were higher in Fantasia than in Jalousia during the second rapid growth stage (from 100 DAB to maturity). The and low pH. PEPC may participate in the control of organic acid accumulation during fruit development in the normal-acid expression of phosphoenolpyruvate carboxylase (PEPC, EC fruit of Fantasia. However, mechanisms other than organic 4.1.1.31), which is involved in organic acid synthesis, was studied during peach fruit development. PEPC mRNA levels, acid synthesis might account for the differences in acidity and protein levels on a total soluble protein basis, peaked at between normal-acid and non-acid peach fruit.