Sugars are necessary for plant growth and fruit development. Cucumber (Cucumis sativus L.) transports sugars, mainly raffinose family oligosaccharides (RFOs), in the vascular bundle. As the dominant sugars in cucumber fruit, glucose and fructose are derived from sucrose, which is the product of RFO hydrolysis by α-galactosidase (α-Gal). Here, we characterized the cucumber alkaline α-galactosidase 2 (CsAGA2) gene and found that CsAGA2 has undergone human selection during cucumber domestication. Further experiments showed that the expression of CsAGA2 increases gradually during fruit development, especially in fruit vasculature. In CsAGA2-RNA interference (RNAi) lines, fruit growth was delayed because of lower hexose production in the peduncle and fruit main vascular bundle (MVB). In contrast, CsAGA2-overexpressing (OE) plants displayed bigger fruits. Functional enrichment analysis of transcriptional data indicated that genes related to sugar metabolism, cell wall metabolism, and hormone signaling were significantly downregulated in the peduncle and fruit MVBs of CsAGA2-RNAi plants. Moreover, downregulation of CsAGA2 also caused negative feedback regulation on source leaves, which was shown by reduced photosynthetic efficiency, fewer plasmodesmata at the surface between mesophyll cell and intermediary cell (IC) or between IC and sieve element, and downregulated gene expression and enzyme activities related to phloem loading, as well as decreased sugar production and exportation from leaves and petioles. The opposite trend was observed in CsAGA2-OE lines. Overall, we conclude that CsAGA2 is essential for cucumber fruit set and development through mediation of sugar communication between sink strength and source activity.
A novel heteropolysaccharide from Grifola frondosa named GFP-W has been isolated and purified by DEAE Sephadex A-52 chromatography. Gas chromatography, fourier transform infrared spectroscopy, one-dimensional (H- and C-) and two-dimensional (H-H COSY, H-C HSQC, and H-C HMBC) nuclear magnetic resonance spectroscopy were used to characterize its structure. The average molecular weight of GFP-W was 66.1 kDa. GFP-W mainly contained four kinds of linkage type units as β-D-GlcpA→, 1,2,6-α-Gal, →2)-α-Manp→, and →3)-α-L-Fucp-(1→. It could significantly increase the uptake of glucose in dexamethasone induced insulin resistant HepG2 cells by improving the mRNA and protein expression of insulin receptor substrate 1, phosphatidylinositol-3-kinase, and glucose transporter 4 upregulation and c-Jun N-terminal Kinase 1 downregulation. Moreover, antidiabetic activities of GFP-W were associated with significant changes in the extent of protein lysine acetylation, crotonylation, and succinylation levels. Our results provide a new hypoglycemic therapeutic role and an in-depth analysis on molecular mechanisms upon polysaccharides from G. frondosa.
Two experiments were conducted to investigate the effect of dietary supplementation with alpha-galactosidase preparation and stachyose on growth performance, nutrient digestibility and intestinal bacterial populations of piglets. In Experiment I 72 crossbred piglets were allotted to three treatments, i.e. 1) control (basal) diet, 2) alpha-Gal1 and 3) alpha-Gal5, the basal diet supplemented with 0.01% and 0.05% alpha-galactosidase preparation (alpha-Gal), respectively. Average daily gain, average daily feed intake and feed conversion ratio were not influenced by alpha-Gal supplementation. In Experiment II 72 crossbred weanling piglets were randomly assigned to four treatments with a complete factorial design, i.e. 1) basal diet, 2) basal diet with 0.01% alpha-Gal supplementation, 3) basal diet with 1% stachyose supplementation and 4) basal diet with 1% stachyose and 0.01% alpha-Gal supplementation. Average daily gain and feed conversion ratio were influenced by alpha-Gal and stachyose supplementation. The ileal digestibility of stachyose, raffinose, gross energy and crude protein was improved significantly by alpha-Gal supplementation. The microbial populations in the intestine were modified by both alpha-Gal and stachyose supplementation. The data suggested that stachyose supplementation had an adverse effect on the growth performance of piglets and alpha-Gal supplementation could ameliorate it, especially in younger pigs.
