Sugar Loading Research Articles

Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip.

Vascular plants rely on differences in osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Münch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem sugar concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems, counterintuitively, to occur by means of passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the non-linear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, the phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Münch transport, where the phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.

Nutritional quality of dietary patterns of children: are there differences inside and outside school?

ObjectivesTo describe the dietary patterns of children inside and outside school and investigate their associations with sociodemographic factors and nutritional status. MethodsThis was a multicenter cross‐sectional study in which children of both sexes, aged 1–6 years, attending private and public daycare centers and preschools in Brazil, were evaluated (n=2979). Demographic, socioeconomic and dietary data (weighed food records and estimated food records) were collected. Dietary patterns were derived by factor analysis from 36 food groups. ResultsFour dietary patterns were identified inside school, and three outside. Inside school, the “traditional” pattern was associated to low income and presented high nutritional quality. The “dual” pattern was associated with low income and with high intake of added sugar and glycemic load. The “snack” pattern was associated with children enrolled at private schools and with high intake of added sugar and glycemic load. The “bread and butter” pattern was associated with high intake of added sugar and trans fat. Outside school, the “traditional” pattern was associated with high intake of saturated fat, trans fats, sodium, and total fiber. The “bread and butter” pattern was associated with high intake of trans fats and glycemic load, whereas the “snack” pattern was associated with overweight, private schools, high income, and high intake of trans fats, sodium, and total fiber. ConclusionThere are differences in the nutritional quality of dietary patterns inside and outside school, and heterogeneity in adherence to these patterns were observed across regions and socioeconomic classes.

Interactive Influence of Enzyme Loading and Initial Concentration of Fermentable Sugars on Simultaneous Saccharification and Fermentation of Cellulose to Ethanol

Interactive Influence of Enzyme Loading and Initial Concentration of Fermentable Sugars on Simultaneous Saccharification and Fermentation of Cellulose to Ethanol

Leaf:Fruit Ratio and Vine Water Status Effects on Grenache Noir (Vitis vinifera L.) Berry Composition: Water, Sugar, Organic Acids and Cations

Seasonal variation in the water, sugar, organic acid and cation contents of developing grape berries (Vitis vinifera L. ‘Grenache noir’) under different levels of water supply (with and without deficit irrigation) and leaf:fruit ratios (18, 10 and five leaves per primary shoot, with one bunch per shoot), were investigated over two successive years in Mediterranean conditions (South of France). Fourteen shoots per vine were left for each leaf:fruit ratio level, and each vine was considered as having homogeneous primary shoots. The growth rate of the berries was increased with irrigation. Total dry matter content of the berry was not affected by leaf:fruit ratios, but the sugar loading decreased during berry development with a lower leaf:fruit ratio (five leaves per bunch). Treatments had little effect on organic acid contents and pH. Berry cation accumulation depended on vine water status and not on the total leaf area of the vine. Under irrigated conditions, calcium continued to accumulate in the berries after veraison. This confirms a partial functioning of the berry xylem during the post-veraison period. The seasonal variation in berry composition was less dependent on the leaf:fruit ratio than on the water status of the vine (mainly cations and sugar). This study provides evidence for the importance of plant water status effects on berry composition, irrespective of the leaf:fruit ratio. Vine water status is a major regulating factor for source-sink relationships.

Preparation of Aluminum Oxide-Coated Glass Slides for Glycan Microarrays.

In this study, we report the fabrication of aluminum oxide-coated glass (ACG) slides for the preparation of glycan microarrays. Pure aluminum (Al, 300 nm) was coated on glass slides via electron-beam vapor deposition polymerization (VDP), followed by anodization to form a thin layer (50–65 nm) of aluminum oxide (Al-oxide) on the surface. The ACG slides prepared this way provide a smooth surface for arraying sugars covalently via phosphonate formation with controlled density and spatial distance. To evaluate this array system, a mannose derivative of α-5-pentylphosphonic acid was used as a model for the optimization of covalent arraying based on the fluorescence response of the surface mannose interacting with concanavalin A (ConA) tagged with the fluorescence probe A488. The ACG slide was characterized using scanning electron microscopy, atomic force microscopy (AFM), and ellipsometry, and the sugar loading capacity, uniformity, and structural conformation were also characterized using AFM, a GenePix scanner, and a confocal microscope. This study has demonstrated that the glycan array prepared from the ACG slide is more homogeneous with better spatial control compared with the commonly used glycan array prepared from the N-hydroxysuccinimide-activated glass slide.

Effects of sitagliptin as initial therapy in newly diagnosed elderly type 2 diabetics: A randomized controlled study.

The objective of this study was to investigate the characteristics of blood glycemic excursion, incretins and pancreatic hormone secretion in elderly people with newly diagnosed type 2 diabetes mellitus (T2DM) and to study the effects of sitagliptin on glycemic excursion in these subjects. A total of 129 newly diagnosed T2DM patients were enrolled in the study from March 2012 to August 2013. Clinical data, serum incretin, pancreatic hormone and continuous glucose monitoring data were collected. Among these subjects, elderly patients (NEDM) randomly received metformin combined with sitagliptin phosphate or glimepiride for 24 weeks. The blood glucose, glycosylated hemoglobin A1c (GHbA1c), serum incretins and pancreatic hormone levels were determined. During the oral glucose tolerance test (OGTT), 30 min insulin and C-peptide levels, 120 min insulin levels and ratio of the increases of insulin and blood glucose levels after 30 min of sugar loading (∆Ins30/∆Glu30) were significantly lower in elderly patients than in middle-aged patients (P<0.05). In addition, the glucagon elevation at 30 min was higher and the glucagon-like peptide-1 (GLP-1) at 30 min was lower in the elderly patients (P<0.05). Glucose excursion indices, including the standard deviation of the average blood glucose, intraday mean average glucose excursions (MAGE), and mean of daily differences (MODD), were significantly higher in the elderly patients (P<0.05). During the OGTT, insulin, C-peptide and ∆Ins30/∆Glu30 results at 30 min and GLP-1 levels at 120 min in NEDM subjects were significantly increased (P<0.05) and glucagon levels at 30 min was significantly lower after sitagliptin treatment (P<0.05) compared with glimepiride. Moreover, MAGE and MODD were significantly lower in the sitagliptin group after treatment compared to those in the glimepiride group (P<0.05). No severe hypoglycemia or cardiovascular diseases were observed. Strong blood glucose excursions occur in elderly patients with newly diagnosed T2DM. Sitagliptin phosphate combined with metformin effectively and safely improves glycemic excursion and carbohydrate metabolism in NEDM patients by promoting the first phase of insulin and incretin secretion and inhibiting glucagon secretion of.

Proteomics and metabolomics analyses reveal the cucurbit sieve tube system as a complex metabolic space.

The plant vascular system, and specifically the phloem, plays a pivotal role in allocation of fixed carbon to developing sink organs. Although the processes involved in loading and unloading of sugars and amino acids are well characterized, little information is available regarding the nature of other metabolites in the sieve tube system (STS) at specific sites along the pathway. Here, we elucidate spatial features of metabolite composition mapped with phloem enzymes along the cucurbit STS. Phloem sap (PS) was collected from the loading (source), unloading (apical sink region) and shoot-root junction regions of cucumber, watermelon and pumpkin. Our PS analyses revealed significant differences in the metabolic and proteomic profiles both along the source-sink pathway and between the STSs of these three cucurbits. In addition, metabolite profiles established for PS and vascular tissue indicated the presence of distinct compositions, consistent with the operation of the STS as a unique symplasmic domain. In this regard, at various locations along the STS we could map metabolites and their related enzymes to specific metabolic pathways. These findings are discussed with regard to the function of the STS as a unique and highly complex metabolic space within the plant vascular system.

Nutritional quality of dietary patterns of children: are there differences inside and outside school?

ObjectivesTo describe the dietary patterns of children inside and outside school and investigate their associations with sociodemographic factors and nutritional status. MethodsThis was a multicenter cross-sectional study in which children of both sexes, aged 1–6 years, attending private and public daycare centers and preschools in Brazil, were evaluated (n=2979). Demographic, socioeconomic and dietary data (weighed food records and estimated food records) were collected. Dietary patterns were derived by factor analysis from 36 food groups. ResultsFour dietary patterns were identified inside school, and three outside. Inside school, the “traditional” pattern was associated to low income and presented high nutritional quality. The “dual” pattern was associated with low income and with high intake of added sugar and glycemic load. The “snack” pattern was associated with children enrolled at private schools and with high intake of added sugar and glycemic load. The “bread and butter” pattern was associated with high intake of added sugar and trans fat. Outside school, the “traditional” pattern was associated with high intake of saturated fat, trans fats, sodium, and total fiber. The “bread and butter” pattern was associated with high intake of trans fats and glycemic load, whereas the “snack” pattern was associated with overweight, private schools, high income, and high intake of trans fats, sodium, and total fiber. ConclusionThere are differences in the nutritional quality of dietary patterns inside and outside school, and heterogeneity in adherence to these patterns were observed across regions and socioeconomic classes.

Production and Investigation of Biochemical and Organoleptic Changes of Mixed Fruit Juice during Storage Period

A blend of different fruits has a great specialty on its splendid color, flavor, taste and nutritional contents. The purpose of this study was to explore the acceptable formulation of mixed fruit juice with better storage stability. The mixed fruit juice samples were prepared in four formulations incorporating pineapple, papaya, banana and orange with the addition of sugar (10%) and sodium benzoate (0.08%). Then the juices were heated for 5 minutes at 65oC, bottled in air tight plastic bottle and stored at 4oC for 180 days and 25oC for 120 days. It was found that TSS, acidity, total sugar, and bacterial load increased slightly, but vitamin C and pH decreased gradually during the storage periods. Fading of color and off flavor was found at the end of storage period. The storage temperature of 4oC was more effective to hold the quality of juice samples against biochemical changes. T 4 sample showed better retention of vitamin C, pH, acidity and total sugar than other samples both at 4oC and 25oC. Panelists preferred the T4 sample most, which showed maximum hedonic scale ‘8’ point on sensory properties. It is also observed that T 4 ensured the better shelf life to preserve the color, flavor and taste until 150 days at 4oC and 105 days at 25oC.

Dietary micronutrient intake during pregnancy is a function of carbohydrate quality

Despite normal gestational weight gain, dietary studies in pregnant women show intakes below the recommendations for energy and micronutrients. This study compared changes in dietary intake from the second to third trimester with emphasis on energy intake and carbohydrate quality. These post hoc analyses were based on 566 women participating in the Pregnancy and Glycemic Index Outcomes study, a randomized controlled trial comparing the effect of low-glycemic index (GI) dietary advice with healthy eating advice on selected pregnancy outcomes. With the use of multilevel mixed-regression analysis, changes in total energy intake, starch, sugar, fiber intake, GI, and glycemic load (GL) were correlated with intake of different micronutrients. Energy intake decreased in the third trimester, and most women did not meet the national recommended amounts for iron, folate, and dietary fiber from food sources alone. After adjustment for age, ethnicity, prepregnancy body mass index, and intervention group, change in energy intake was positively related to change in intake of all micronutrients (P < 0.001). GI, GL, and starch intake were inversely related to micronutrient intake (P < 0.001), whereas higher total sugars predicted higher intake (P < 0.001). Associations with dietary fiber were inconsistent. Normal pregnancy can be associated with a decline in energy and micronutrient intake from diet. Low dietary GI and GL were the best predictors of a favorable micronutrient profile. This trial was registered at www.anzctr.org.au as ACTRN12610000174088.

Radial stem variations - a source of tree physiological information not fully exploited yet.

Radial stem variations - a source of tree physiological information not fully exploited yet.

Combining stable isotope and carbohydrate analyses in phloem sap and fine roots to study seasonal changes of source-sink relationships in a Mediterranean beech forest.

Carbon isotope composition (δ(13)C) and carbohydrate content of phloem sap and fine roots were measured in a Mediterranean beech (Fagus sylvatica L.) forest throughout the growing season to study seasonal changes of source-sink relationships. Seasonal variations of δ(13)C and content of phloem sap sugars, collected during the daylight period, reflected the changes in soil and plant water status. The correlation between δ(13)C and content of phloem sap sugars, collected from plants belonging to different social classes, was significantly positive only during the driest month of July. In this month, δ(13)C of phloem sap sugars was inversely related to the increment of trunk radial growth and positively related to δ(13)C of fine roots. We conclude that the relationship between δ(13)C and the amount of phloem sap sugars is affected by a combination of causes, such as sink strength, tree social class, changes in phloem anatomy and transport capacity, and phloem loading of sugars to restore sieve tube turgor following the reduced plant water potential under drought conditions. However, δ(13)C and sugar composition of fine roots suggested that phloem transport of leaf sucrose to this belowground component was not impaired by mild drought and that sucrose was in a large part allocated towards fine roots in July, depending on tree social class. Hence, fine roots could represent a functional carbon sink during the dry seasonal periods, when transport and use of assimilates in other sink tissues are reduced. These results indicate a strict link between above- and belowground processes and highlight a rapid response of this Mediterranean forest to changes in environmental drivers to regulate source-sink relationships and carbon sink capacity.

Metabolic Syndrome (MetS) in an HIV Cohort on Antiretroviral Therapy (ART)

ObjectiveThe purpose of this study was to evaluate the prevalence of MetS characteristics, and factors associated with the presence of MetS, in 89 people living with HIV (PLWH) on ART enrolled in a community‐based exercise training and nutrition education program targeting individuals of low socioeconomic status.ResultsOne in three PLWH met Adult Treatment Panel (ATP) III criteria for MetS and it was mostly due to high waist circumference and elevated blood pressure. Higher use of protease inhibitors, elevated hemoglobin A1C (HbA1c), greater self‐reported daily caloric intake and consumption of carbohydrates, sugar, added sugar, and higher glycemic load were found among the individuals with MetS, compared to those without it. Elevated HbA1c and high total sugar consumption were the strongest predictors and accounted for 30% of the occurrence of MetS.ConclusionsThe overall prevalence of MetS observed was higher than previously reported in the general population and other PLWH cohorts. Additional work is needed to determine whether MetS is a more disease/treatment or lifestyledependent condition in PLWH. This material is based on work supported by AstraZeneca HealthCare Foundation's Connections for Cardiovascular Health SM(CCH) program.

A cross-sectional assessment of metabolic syndrome in HIV-infected people of low socio-economic status receiving antiretroviral therapy.

BackgroundMetabolic syndrome (MetS) is a constellation of symptoms used as a measure to identify patients at increased risk for cardiovascular disease, type 2 diabetes, and all-cause mortality. The results of prolonged life expectancy and cumulative toxic effects of antiretroviral therapy increase the chance that HIV can cause clinical abnormalities, including MetS.MethodsWe evaluated 89 people living with HIV (PLWH; mean age 48 ± 7 years; mean duration of HIV infection 17 ± 12 years; 47% men; 66% African-American, 22% Hispanic, and 10% non-Hispanic white; and 84% unemployed) enrolled in a community-based exercise training and nutrition education program targeting individuals of low socio-economic status (SES). The prevalence of MetS characteristics and the factors associated with the presence of MetS were analyzed.ResultsOne in three (33%; 12 men and 17 women) PLWH met ATPIII criteria for MetS. In our cohort, MetS was driven by high waist circumference and elevated blood pressure. In addition, higher use of protease inhibitors, elevated hemoglobin A1c (HbA1c), greater self-reported daily caloric intake and consumption of carbohydrates, sugar, added sugar, and higher glycemic load were found among the individuals with MetS, compared to those without it. Elevated HbA1c and high total sugar consumption were the strongest predictors and accounted for 30% of the occurrence of MetS.ConclusionsThe overall prevalence of MetS in our PLWH cohort receiving antiretroviral therapy is higher than previously reported in the general population and in other PLWH cohorts. Additional work is needed to determine whether MetS is a more disease dependent or lifestyle dependent condition in PLWH.

Extraction of Apoplastic Wash Fluids and Leaf Petiole Exudates from Leaves of Arabidopsis thaliana

The long-distance translocation of metabolites and mineral elements is crucial for plant growth and reproduction. In most cases, source-to-sink translocation of metabolites and minerals requires their passage through the apoplast, irrespective whether they are transported via the xylem or the phloem. This apoplast-mediated pathway is of particular importance during plant senescence, when photoassimilates as well as organic, inorganic or chelated forms of nutrients are translocated from leaves to fruits or seeds. Recent genetic and physiological studies revealed the involvement of numerous membrane transporters mediating phloem loading of amino acids, sugars, urea or mineral elements. To evaluate the contribution of individual transporters to xylem unloading or phloem loading, the collection of apoplastic fluids and of phloem sap is essential. Here, we describe a method for the extraction of apoplastic fluids and the collection of leaf petiole exudates from Arabidopsis leaves, the latter representing an approximation to the real composition of the phloem sap.

Mathematical modelling of the Phloem: the importance of diffusion on sugar transport at osmotic equilibrium.

Plants rely on the conducting vessels of the phloem to transport the products of photosynthesis from the leaves to the roots, or to any other organs, for growth, metabolism, and storage. Transport within the phloem is due to an osmotically-generated pressure gradient and is hence inherently nonlinear. Since convection dominates over diffusion in the main bulk flow, the effects of diffusive transport have generally been neglected by previous authors. However, diffusion is important due to boundary layers that form at the ends of the phloem, and at the leaf-stem and stem-root boundaries. We present a mathematical model of transport which includes the effects of diffusion. We solve the system analytically in the limit of high Münch number which corresponds to osmotic equilibrium and numerically for all parameter values. We find that the bulk solution is dependent on the diffusion-dominated boundary layers. Hence, even for large Péclet number, it is not always correct to neglect diffusion. We consider the cases of passive and active sugar loading and unloading. We show that for active unloading, the solutions diverge with increasing Péclet. For passive unloading, the convergence of the solutions is dependent on the magnitude of loading. Diffusion also permits the modelling of an axial efflux of sugar in the root zone which may be important for the growing root tip and for promoting symbiotic biological interactions in the soil. Therefore, diffusion is an essential mechanism for transport in the phloem and must be included to accurately predict flow.

Leaf architectural, vascular and photosynthetic acclimation to temperature in two biennials

Acclimation of leaf features to growth temperature was investigated in two biennials (whose life cycle spans summer and winter seasons) using different mechanisms of sugar loading into exporting conduits, Verbascum phoeniceum (employs sugar-synthesizing enzymes driving symplastic loading through plasmodesmatal wall pores of phloem cells) and Malva neglecta (likely apoplastic loader transporting sugar via membrane transport proteins of phloem cells). In both species, acclimation to lower temperature involved greater maximal photosynthesis rates and vein density per leaf area in close correlation with modification of minor vein cellular features. While the symplastically loading biennial exhibited adjustments in the size of minor leaf vein cells (consistent with adjustment of the level of sugar-synthesizing enzymes), the putative apoplastic biennial exhibited adjustments in the number of cells (consistent with adjustment of cell membrane area for transporter placement). This upregulation of morphological and anatomical features at lower growth temperature likely contributes to the success of both the species during the winter. Furthermore, while acclimation to low temperature involved greater leaf mass per area in both species, this resulted from greater leaf thickness in V. phoeniceum vs a greater number of mesophyll cells per leaf area in M. neglecta. Both types of adjustments presumably accommodate more chloroplasts per leaf area contributing to photosynthesis. Both biennials exhibited high foliar vein densities (particularly the solar-tracking M. neglecta), which should aid both sugar export from and delivery of water to the leaves.

Capsaicin as new orally applicable gastroprotective and therapeutic drug alone or in combination with nonsteroidal anti-inflammatory drugs in healthy human subjects and in patients.

Capsaicin is a specific compound acting on capsaicin-sensitive afferent nerves. Capsaicin was used to study the different events of human gastrointestinal physiology, pathology, and clinical pharmacology, and possible therapeutic approaches to enhance gastrointestinal mucosal defense in healthy human subjects and in patients with various different gastrointestinal disorders as well as its use with nonsteroidal anti-inflammatory drugs (NSAIDs) in healthy subjects and in patients. The observations were carried out in 198 healthy human subjects and in 178 patients with different gastrointestinal (GI) diseases (gastritis, erosions, ulcer, polyps, cancer, inflammatory bowel diseases, colorectal polyps, cancers), and in 69 patients with chronic (Helicobacter pylori positive and negative) gastritis (before and after eradication treatment). The gastric secretory responses and their chemical composition, gastric emptying, sugar loading test, gastric transmucosal potential difference (GTPD) with application of capsaicin alone, after ethanol alone and with capsaicin, indomethacin-induced gastric mucosal microbleeding without and with capsaicin were studied. The immunohistochemical examinations of the capsaicin receptor (TRVP1), calcitonin gene- related peptide (CGRP), and substance P (SP) were carried out in gastrointestinal tract, and especially in patients with chronic gastritis (with and without Helicobacter infection, before and after classical eradication treatment). Classical molecular pharmacological methods were applied to study the drugs inhibiting the gastric basal acid output. Capsaicin decreased the gastric basal output, enhanced the "non-parietal" (buffering) component of gastric secretory responses, and gastric emptying, and the release of glucagon. Capsaicin prevented the indomethacin- and ethanol-induced gastric mucosal damage; meanwhile capsaicin itself enhanced (GTPD). Capsaicin prevented the indomethacin-induced gastric mucosal microbleeding. The expression of TRVP1 and CGRP increased in the gastric mucosa of patients with chronic gastritis (independently of the presence of Helicobacter pylori infection), and the successfully carried out eradication treatment. The human first phase examinations (the application of acetylsalicylic acid (ASA), diclqfenac, and naproxen together with capcaicinoids) (given in doses that stimulate capsaicin-sensitive afferent vagal nerves) showed no change in the pharmacokinetic parameters of ASA and diclofenac and the ASA and diclofenac-induced platelet aggregation. Capsaicin represents a new orally applicable gastroprotective agent in healthy human subjects and in patients with different chemical and Helicobacter pylori-induced mucosal damage and in many other diseases requiring treatment with NSAIDs.

Rice sucrose transporter1 (OsSUT1) up‐regulation in xylem parenchyma is caused by aphid feeding on rice leaf blade vascular bundles

The role of the sucrose transporter OsSUT1 in assimilate retrieval via the xylem, as a result of damage to and leakage from punctured phloem was examined after rusty plum aphid (Hysteroneura setariae, Thomas) infestation on leaves from 3-week-old rice (Oryza sativa L.cv Nipponbare) plants. Leaves were examined over a 1- to 10-day infestation time course, using a combination of gene expression and β-glucuronidase (GUS) reporter gene analyses. qPCR and Western blot analyses revealed differential expression of OsSUT1 during aphid infestation. Wide-field fluorescence microscopy was used to confirm the expression of OsSUT1-promoter::GUS reporter gene in vascular parenchyma associated with xylem elements, as well as in companion cells associated with phloem sieve tubes of large, intermediate and small vascular bundles within the leaf blade, in regions where the aphids had settled and were feeding. Of great interest was up-regulation of OsSUT1 expression associated with the xylem parenchyma cells, abutting the metaxylem vessels, which confirmed that OsSUT1 was not only involved in loading of sugars into the phloem under normal physiological conditions, but was apparently involved in the retrieval of sucrose leaked into the xylem conduits, which occurred as a direct result of aphid feeding, probing and puncturing of vascular bundles. The up-regulation of OsSUT1 in xylem vascular parenchyma thus provides evidence in support of the location within the xylem parenchyma cells of an efficient mechanism to ensure sucrose recovery after loss to the apoplast (xylem) after aphid-related feeding damage and its transfer back to the symplast (phloem) in O.sativa leaves.

Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders.

Plasmodesmata (PD) play a key role in loading of sugars into the phloem. In plant species that employ the so-called active symplasmic loading strategy, sucrose that diffuses into their unique intermediary cells (ICs) is converted into sugar oligomers. According to the prevalent hypothesis, the oligomers are too large to pass back through PD on the bundle sheath side, but can pass on into the sieve element to be transported in the phloem. Here, we investigate if the PD at the bundle sheath-IC interface can indeed fulfill the function of blocking transport of sugar oligomers while still enabling efficient diffusion of sucrose. Hindrance factors are derived via theoretical modeling for different PD substructure configurations: sub-nano channels, slit, and hydrogel. The results suggest that a strong discrimination could only be realized when the PD opening is almost as small as the sugar oligomers. In order to find model parameters that match the in vivo situation, we measured the effective diffusion coefficient across the interface in question in Cucurbita pepo with 3D-photoactivation microscopy. Calculations indicate that a PD substructure of several sub-nano channels with a radius around 7 Å, a 10.4 Å-wide slit or a hydrogel with 49% polymer fraction would be compatible with the effective diffusion coefficient. If these configurations can accommodate sufficient flux of sucrose into the IC, while blocking raffinose and stachyose movement was assessed using literature data. While the slit-configuration would efficiently prevent the sugar oligomers from “leaking” from the IC, none of the configurations could enable a diffusion-driven sucrose flux that matches the reported rates at a physiologically relevant concentration potential. The presented data provides a first insight on how the substructure of PD could enable selective transport, but indicates that additional factors are involved in efficient phloem loading in active symplasmic loading species.