Crystal structure of Arabidopsis thaliana neutral invertase 2

The metabolism of sucrose is of crucial importance for life on Earth. In plants, enzymes called invertases split sucrose into glucose and fructose, contributing to the regulation of metabolic fluxes. Invertases differ in their localization and pH optimum. Acidic invertases present in plant cell walls and vacuoles belong to glycoside hydrolase family 32 (GH32) and have an all-β structure. In contrast, neutral invertases are located in the cytosol and organelles such as chloroplasts and mitochondria. These poorly understood enzymes are classified into a separate GH100 family. Recent crystal structures of the closely related neutral invertases InvA and InvB from the cyanobacterium Anabaena revealed a predominantly α-helical fold with unique features compared with other sucrose-metabolizing enzymes. Here, a neutral invertase (AtNIN2) from the model plant Arabidopsis thaliana was heterologously expressed, purified and crystallized. As a result, the first neutral invertase structure from a higher plant has been obtained at 3.4 Å resolution. The hexameric AtNIN2 structure is highly similar to that of InvA, pointing to high evolutionary conservation of neutral invertases.

Sucrose metabolism in the subtending leaf to cotton boll at different fruiting branch nodes and the relationship to boll weight

SUMMARYChanges of sucrose metabolism in the subtending leaf to cotton (Gossypium hirsutum L.) boll at different fruiting branch nodes (FBN) were investigated. Two cotton cultivars, Kemian 1 and Sumian 15, were grown in the field at three planting dates in 2009 and 2011. Cotton planted on different dates but experiencing similar climatic factors flowered on the same date and had similar boll opening dates, but had different FBN. In the present study, boll weight and carbohydrate content were significantly affected by both flowering date (FD) and FBN. However, only cystolic fructose-1,6-bisphosphatase (cy-FBPase) and sucrose-phosphate synthase (SPS) activities of the sucrose-metabolizing enzymes were influenced significantly by FBN, and the influence of FBN was lower with delayed FD. In general, effects of FBN on boll weight and sucrose metabolism in the subtending leaf were higher at the optimal FD (13 August) than those at later FD (9 September 2009 and 2 September 2011), and total fruiting branches were used to characterize cotton physiological age in the current study. Sucrose transport capacity (Tn) and SPS in the subtending leaf had significantly positive correlations with boll weight at 17–24 days post anthesis (DPA), a crucial period when boll weight was significantly affected. In addition, higher SPS activity was favourable for sucrose export and boll weight during boll development.

Influence of Arbuscular Mycorrhizal Fungi on Sucrose Metabolism of Citrus Seedlings

The effects of arbuscular mycorrhizal fungi (AMF, Glomus mosseae) on plant dry weights, sucrose and glucose concentrations, and sucrose-metabolizing enzyme (AI-acid invertase; NI-neutral invertase; SS-sucrose synthase) activities were examined in young citrus (Citrus junos Sieb.ex Tanaka) seedlings. After three months of mycorrhizal inoculation, root mycorrhizal colonization was 55.32%. Inoculation with G. mosseae significantly increased shoot and root dry weights and sucrose and glucose concentrations in leaf and root, compared with non-AMF seedlings. AMF colonization was significantly positively correlated with glucose and sucrose concentrations of leaf and root, suggesting that AM symbosis alters carbohydrate concentrations to sustain symbiosis development. On the other hand, AMF colonization significantly increased root AI and leaf SS activities, but decreased leaf AI and NI activities and root NI and SS activities. Based on the correlation analysis, it assumes that AMF regulated the carbohydrate concentrations for the plant growth and mycorrhizal development through altering activities of the sucrose-metabolizing enzymes.