甜菊花药壁的超微结构及功能研究

1.甜菊花药发育至四分体时期,绒毡层细胞达最大程度的发育。细胞器丰富且呈活跃状态,脂肪微粒沿内切向面和径向面沉积。2.绒毡层周原质团具有大量呈现活跃功能的细胞器,并不断积累各种物质,其RNA和蛋白质合成能力亦较强,认为周原质团有一定的重组行为。3.发育早期药室内壁细胞结构较简单,但至周原质团物质将被小孢子完全吸收时,其内质网和高尔基体剧增,RNA和蛋白质合成能力亦骤然增强,认为此时药室内壁细胞对花粉发育起供养作用。     

Impact of nitrogen supply on growth,steviol glycosides and photosynthesis in Stevia rebaudiana Bertoni

This work investigated the agronomic, physiological and biochemical response of Stevia rebaudiana Bertoni grown under different nitrogen (N) rates. A pot trial in open air conditions was set up in 2012 with the aim to evaluate the effect of four N rates on the biometric and productive characteristics, steviol glycoside (SG) content as well as on leaf gas exchanges, chlorophyll fluorescence, photosynthetic pigments, Rubisco activity and N use efficiency. N deficiency caused a decrease in leaf N content, chlorophylls and photosynthetic CO₂ assimilation, resulting in a lower dry matter accumulation as well as in reduced SG production. The application of 150 kg N ha^? 1 seems to be the most effective treatment to improve rebaudioside A (Reb A) content, Reb A/stevioside ratio, photosynthetic CO₂ assimilation, stomatal conductance, N use efficiency, ribulose-1,5-bis-phosphate carboxylase/oxygenase (Rubisco) and PSII efficiency. The results demonstrate that by using an appropriate N rate it is possible to modulate the SG biosynthesis, with a significant increase in the Reb A content and in the ratio between Reb A and stevioside. This finding is of great relevance in order to obtain a raw material designed to meet consumer needs and bio-industry requirements for high-quality, Reb A content, and safe and environmentally friendly products.     

A functional (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase exhibits diurnal regulation of expression in Stevia rebaudiana (Bertoni)

The leaves of stevia [Stevia rebaudiana (Bertoni)] are a rich source of steviol glycosides that are used as non-calorific sweetener in many countries around the world. Steviol moiety of steviol glycosides is synthesized via plastidial 2C-methyl-D-erythritol 4-phosphate pathway, where (E)-4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR) is the key enzyme. HDR catalyzes the simultaneous conversion of (E)-4-hydroxy-3-methylbut-2-enyl diphosphate into five carbon isoprenoid units, isopentenyl diphosphate and dimethylallyl diphosphate. Stevia HDR (SrHDR) successfully rescued HDR lethal mutant strain MG1655 ara<>ispH upon genetic complementation, suggesting SrHDR to encode a functional protein. The gene exhibited diurnal variation in expression. To identify the possible regulatory elements, upstream region of the gene was cloned and putative cis-acting elements were detected by in silico analysis. Electrophoretic mobility shift assay, using a putative light responsive element GATA showed the binding of nuclear proteins (NP) isolated from leaves during light period of the day, but not with the NP from leaves during the dark period. Data suggested the involvement of GATA box in light mediated gene regulation of SrHDR in stevia.     

Immune up regulatory response of a non-caloric natural sweetener, stevioside

Immunomodulation is a process, which alters the immune system of an organism by interfering with its functions. This interference results in either immunostimulation or immunosuppression. An immunomodulator is any substance that helps to regulate the immune system. This “regulation” is a normalization process, so that an immunomodulator helps to optimise immune response. Immunomodulators are becoming very popular in the worldwide natural health industry as these do not tend to boost immunity, but to normalize it. Keeping this in view, major efforts have to be directed to modulate the immune responses, to permit effective treatment of various ailments associated with immune system and thus the development of a safe and effective immunomodulator for clinical us.

Leaves of Stevia rebaudiana are a source of several sweet glycosides of steviol. The major glycoside, stevioside, diterpenoid glycoside—is used in oriental countries as a food sweetener. Its medical use is also reported as a heart tonic. Besides, it is used against obesity, hypertension, and stomach burn and to lower uric acid levels. Here in this study, stevioside was tested for its immunomodulatory activity on different parameters of the immune system at three different doses (6.25, 12.5 and 25 mg/kg p.o.) on normal as well as cyclophosphamide treated mice. Stevioside was found effective in increasing phagocytic activity, haemagglutination antibody titre and delayed type hypersensitivity. In parallel, stevioside substantially increase proliferation in the LPS and Con A stimulated B and T cells, respectively. Present study, therefore, reveals that the drug holds promise as immunomodulating agent, which acts by stimulating both humoral as well as cellular immunity and phagocytic function.     

The positive role of steviol glycosides in stevia (Stevia rebaudiana Bertoni) under drought stress condition

Steviol glycosides (SVglys) are a group of diterpenoids mainly present in the leaves of stevia (Stevia rebaudiana Bertoni). An experiment was conducted to find the functional role of SVglys compounds in stevia affected by drought stress. In this study, a liquid blend of SVglys (200 ppm) was sprayed on stevia plants grown in well-watered (90% field capacity) and drought-stress conditions (45% field capacity) and then the morphological traits and metabolites were evaluated. It was observed that leaf losses caused by drought stress were stopped through external application of SVglys and consequently the harvest index of stevia was increased. Metabolite analysis of stevia leaves showed that the total SVglys content was significantly decreased due to drought stress, but was compensated by external application of SVglys. Among the SVglys, Rebaudioside A responded more to external SVglys. A slight promotion in total antioxidant activity of stevia leaves was observed when external SVglys was applied. The glucose availability in stevia leaves was increased by external application of SVglys but only in well-watered plants. According to our findings, it can be concluded that in stevia, SVglys may have a positive function in drought stress tolerance by exerting a protective role under such conditions.     

R－A型甜菊糖甙的研制

以甜菊（ＳｔｅｖｉａｒｅｂａｕｄｉａｎａＢｅｒｔｏｎｉ）的干叶为原料生产的甜菊糖甙是一种食用天然甜味剂。提高甜菊糖甙（Ｓｔｅｖｉｏｓｉｄｅｓ）中优质甜味成分Ｒ－Ａ（甜菊Ａ３甙：ＲｅｂａｕｄｉｏｓｉｄｅＡ）的含量比例是生产中急待解决的课题。本文以Ｒ－Ａ型和Ｓｔ（甜菊甙Ｓｔｅｖｉｏｓｉｄｅ）型甜菊叶为原料,采用Ａ和Ｂ两种方法进行甜菊糖甙的提取,通过Ｂ法获得Ｒ－Ａ含量比例高的甜菊糖甙即Ｒ－Ａ型甜菊糖甙,为甜菊糖甙产品优质化提供了新方法、新技术     

甜菊醇糖苷生物合成关键基因的导入和鉴定分析

甜叶菊（Stevia rebaudiana Bertoni）生产的甜菊醇糖苷因具有高甜度、低热能、不参与人体内代谢兼具保健功能等特点,被誉为最有发展前途的新糖源。从甜叶菊叶片克隆了甜菊醇糖苷生物合成途径中的关键基因SrUGT85C2、SrUGT91D2m和SrUGT76G1,构建植物基因过量表达载体,以单独或组合的形式将这些基因导入到甜叶菊中,获得转基因植株。与野生型对照植株相比,单独导入SrUGT85C2的转基因植株中甜菊醇单糖苷含量提高,总糖苷、莱包迪苷A含量及占比没有明显变化;单独导入SrUGT91D2m的转基因植株中甜菊醇单糖苷含量显著降低,而甜菊醇双糖苷含量显著增加;单独导入SrUGT76G1的转基因植株中,总糖苷含量显著提高,莱包迪苷A含量达到10%以上,比对照提高了2倍,而甜菊糖苷含量减少了一半。3个基因组合同时导入的转基因甜叶菊植株与单独导入SrUGT76G1的转基因甜叶菊植株类似,其总糖苷、莱包迪苷A含量及其占比均显著提高。这些结果为以后通过分子生物学技术来调控甜菊醇糖苷生物合成关键基因的表达,培育莱包迪苷A含量高的高品质甜叶菊新品系提供了理论依据和技术方法。     

Highly Oxygenated Labdane Diterpenoids from Stevia rebaudiana and Their Anti-Atherosclerosis Activities

Five unknown labdane diterpenoids Stevelins A–E ( 1–5 ), three known labdane diterpenoids ( 6–8 ) and three labdane norditerpenoids ( 9–11 ) were isolated from the Stevia rebaudiana. The structures were determined primarily via NMR spectroscopic data and HR-ESI-MS experiments. X-ray crystallography using CuK_α radiation was used to determine the absolute configurations of 1 , and the absolute configurations of 2–5 were deduced by electronic circular dichroism (ECD) calculations. The potential anti-atherosclerosis activities of all compounds were evaluated by measuring their inhibitory effects on the macrophage foam cell formation. As a result, most isolated compounds could significantly inhibit oxidized low-density lipoprotein (ox-LDL)-induced macrophage foam cell formation, which suggests that these compounds may be promising candidates in the treatment for atherosclerosis.     

Phytochemical Analysis,Estimation of Quercetin,and <i>in Vitro</i> Anti-Diabetic Potential of Stevia Leaves Samples Procured from Two Geographical Origins

The current study used RP-HPLC to compare phytochemicals and estimate the bioactive constituents found in Stevia rebaudiana Bert. (SRB) leaves collected from two different geographical sources. SRB leaves were collected from Bangalore, Karnataka, India, and Reduit, Mauritius. Extracts were prepared using ethanol and aqueous solvents. Proximate analysis was used to evaluate moisture content, ash values, crude fibers, and extractive values. Following that, preliminary phytochemical screening was done on both ethanol leaves extracts, and subsequently total flavonoid content was determined. In addition, TLC chromatograms and RP-HPLC studies were performed on both plant extracts to determine the presence of flavonoid components in both leaves extracts, followed by in vitro anti-diabetic activity was performed with alpha amylase and alpha glucosidase enzymes against Acarbose as standard. Results revealed that both the extracts from two different geographical sources varied significantly with the yield, content of chemicals, and presence of quercetin (flavonoid) content when estimated through the RP-HPLC standardized method. Glycosides, flavonoids, proteins, steroids, saponins, terpenoids, and phenols were found in various concentrations during phytochemical screening. Among both zones, the ethanol leaves extract of SRB taken from Mauritius had a greater content of phytochemicals and a higher yield than other extracts due to the soil nature. The Mauritius sample had greater total flavonoid levels as well as more quercetin (0.92 ± 0.011) than the other extracts. Following that, ethanol extract inhibited enzymes (alpha amylase, alpha glucosidases) more than aqueous extract, and this inhibition was dose dependent. Among them, the Mauritius ethanol sample showed higher anti-diabetic efficacy than the Indian sample, but this difference was not significant. Overall, SRB ethanol leaves extracts outperformed other leaves extracts in terms of yield, phytoconstituents, and total flavonoids. Overall, both SRB samples had high quercetin levels and possessed anti-diabetic potential, but they were greater in the Mauritius sample, demonstrating that plant traits are influenced by geographic location.