Abstract
Differences in carbohydrate contents and metabolizing-enzyme activities were monitored in apical, medial, basal and core sections of pineapple (Ananas comosus cv. Comte de paris) during fruit development and ripening. Fructose and glucose of various sections in nearly equal amounts were the predominant sugars in the fruitlets, and had obvious differences until the fruit matured. The large rise of sucrose/hexose was accompanied by dramatic changes in sucrose phosphate synthase (SPS) and sucrose synthase (SuSy) activities. By contrast, neutral invertase (NI) activity may provide a mechanism to increase fruit sink strength by increasing hexose concentrations. Furthermore, two cDNAs of Ac-sps (accession no. GQ996582) and Ac-ni (accession no. GQ996581) were first isolated from pineapple fruits utilizing conserved amino-acid sequences. Homology alignment reveals that the amino acid sequences contain some conserved function domains. Transcription expression analysis of Ac-sps, Ac-susy and Ac-ni also indicated distinct patterns related to sugar accumulation and composition of pineapple fruits. It suggests that differential expressions of multiple gene families are necessary for sugar metabolism in various parts and developmental stages of pineapple fruit. A cycle of sucrose breakdown in the cytosol of sink tissues could be mediated through both Ac-SuSy and Ac-NI, and Ac-NI could be involved in regulating crucial steps by generating sugar signals to the cells in a temporally and spatially restricted fashion.
Highlights
Fruit taste and quality in pineapple (Ananas comosusr) mainly depend upon such factors as sugars, organic acids, firmness, amino acids and aromatic compounds
Three major sugar contents of pineapple fruits were determined throughout development stages
Positive correlation between sugar accumulation (Figure 1) and levels of SuSy and sucrose phosphate synthase (SPS) activities (Figure 6b,c) were indicated in fruit different sections during development, which is paralleled with the transcript characteristics of two genes. These results suggest that sucrose synthase can only cleave the sucrose translocated to fruit tissue at a mature stage, and that neutral invertase (NI) activity is closely related to the accumulation of fructose and glucose in immature pineapple fruit
Summary
Fruit taste and quality in pineapple (Ananas comosusr) mainly depend upon such factors as sugars, organic acids, firmness, amino acids and aromatic compounds. Glucose and fructose synthesized in source tissues are one of the most important sugars, which are transported into sink tissues such as fruit, shoots and other tissues [1]. Sucrose serves an integral role as a source of carbon and energy for non-photosynthetic tissues, which is central to plant metabolism and the most dominant metabolite involved in fruit growth and development [2]. Attempts to elucidate the changes in metabolism that lead to accumulation of sucrose had focused on sucrose-metabolizing enzymes like sucrose phosphate synthase (SPS, EC 2.1.4.14), sucrose synthase (SuSy, EC 2.4.1.13). With the full-length or fragment SPS cDNAs isolated from fewer than 20 plant species from. There is a direct correlation between sucrose accumulation and SPS enzymatic activity, the mechanism of its regulation is unknown during fruit ripening [7]
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