奇甜蛋白基因在园艺作物中的表达

奇甜蛋白（thaumatin）是从非洲西部植物katemfe（Thaumatococcus daniellii Benth）中提取得到的几种关系相近的甜味蛋白的统称,其中最主要的为奇甜蛋白Ⅰ和奇甜蛋白Ⅱ。奇甜蛋白不仅甜度高,而且具有低热量、安全无毒以及不易诱发糖尿病等优点。因此,将奇甜蛋白基因转入园艺作物中并使之表达,用以提高可食部分的甜味,有其特别的研究意义。奇甜蛋白基因已先后在马铃薯、梨树、黄瓜、番茄等园艺作物得到表达,但仍有一些问题需要解决。现从奇甜蛋白基因的克隆、测序与表达,转基因果实的安全性检测,甜度的感官评价,甜味遗传特点以及奇甜蛋白抗真菌病害检验等几个方面综述了国内外研究进展,并对今后的研究提出了建议。     

Optimal concentration of Beauveria bassiana vectored by bumble bees in relation to pest and bee mortality in greenhouse tomato and sweet pepper

Greenhouse cage trials were conducted to determine the optimal concentration of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) (BotaniGard 22WP^® formulation) as vectored by the bumble bee, Bombus impatiens (Cresson) (Hymenoptera: Apidae) pollinator for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) on greenhouse tomato, tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) and green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) on greenhouse sweet pepper. Three inoculum concentrations of B. bassiana: low, 9 × 10⁹; middle, 6.24 × 10¹⁰; and high, 2 × 10¹¹ conidia g^?1 of inoculum and two controls (one with bees and heat-inactivated inoculum, and the other which contained only the host plants and pest species) were tested in a completely randomized block design. Beauveria bassiana killed 18, 54 and 56% of the adult T. vaporariorum and 33, 70 and 67% of the adult L. lineolaris, respectively, at the low, middle and high concentrations; but no infection from B. bassiana occurred in each of the control treatments. Internal infection rates after surface sterilization of the pest insects were 11, 34 and 35% for adult T. vaporariorum, 29, 54 and 58% for adult L. lineolaris, 22, 34 and 30% for nymphal M. persicae and 17, 29 and 32% for nymphal T. vaporariorum, respectively, at the low, middle and high concentrations. Significantly more bumble bees died at the high concentration of B. bassiana (42–45%) than at the other concentrations (9–15%) and the controls (5–7%). Spores of B. bassiana were collected throughout the plant canopy with the greatest numbers sampled from the top third of the canopy [ca. 1,200 colony forming units (CFU) per cm^?2]. The middle concentration was selected as the optimal concentration because it provided the best pest control with the least impact on the bees.     

甘薯质体中的乙酰辅酶A羧化酶亚基基因accD的克隆与序列分析

依据烟草质体全基因组序列设计引物,以甘薯质体基因组DNA为模板,PCR扩增包含质体accD基因完整编码区在内的一段序列（GenBank登录号为GQ395771）。序列分析表明：该片段全长为2209bp,包括1548bp的nccD基因编码序列,推测编码515个氨基酸的蛋白质,该蛋白序列具有异质型β-CT中保守的锌指结构和C末端5个基元。同时绘制了该DNA片段的限制性酶切图谱。相似性比较显示,甘薯accD基因与大豆、马铃薯、拟南芥、人参、莴苣、葡萄、海岛棉、甘蓝、辣椒、菠菜、番茄和烟草的accD基因核苷酸相似性为72％-87％,氨基酸相似性为58％-83％。     

The Effect of the Sequence of Infection of the Causal Agents of Sweet Potato Virus Disease on Symptom Severity and Individual Virus Titres in Sweet Potato cv. Beauregard

Sweet potato virus disease (SPVD) is caused by dual infection of plants with Sweet Potato Feathery Mottle Virus (SPFMV) and Sweet Potato Chlorotic Stunt Virus (SPCSV). Because SPFMV and SPCSV are transmitted by aphids and whiteflies, respectively, infection in nature occurs independently rather than simultaneously. To investigate the effect of consecutive infection on symptom development and individual virus titres, plants infected with a single virus were later inoculated with the second virus. Symptoms were significantly more severe in plants infected with SPCSV followed by SPFMV compared to plants infected with SPFMV followed by SPCSV. Virus titres were not significantly different for SPCSV, but SPFMV titres, in plants infected with SPCSV followed by SPFMV, were significantly higher than all other treatments. The results indicate that the sequence of infection of sweetpotato plants with the causal agents of SPVD influence the severity of symptoms and SPFMV titres in SPVD affected plants.     

Control of postharvest decay on cherry tomatoes by marine yeast Rhodosporidium paludigenum and calcium chloride

Aims: In this study, the potential of calcium chloride (CaCl₂) application to improve the efficacy of the marine antagonist Rhodosporidium paludigenum in controlling postharvest diseases of cherry tomatoes was assessed. Methods and Results: CaCl₂ alone was found not to have any direct influence on the population growth of R. paludigenum in NYDB cultures or in cherry tomato wounds. However, the combined treatments with 1 × 10⁸ cells ml^?1R. paludigenum and CaCl₂ at the concentration from 0·5 to 2% showed high activities to reduce black rot caused by Alternaria alternata in cherry tomato wounds, significantly higher than those of R. paludigenum or CaCl₂ alone. Meanwhile, 0·5% CaCl₂ in combination with 1 × 10⁸ cells ml^?1R. paludigenum greatly inhibited the natural decay of cherry tomatoes in 21 days’ storage at 25°C. Conclusions: The combination of R. paludigenum and CaCl₂ enhances the inhibition of black rot and natural decay of postharvest cherry tomatoes. The results from this study provide a new way to improve the efficiency of R. paludigenum in maintaining the quality of postharvest fruits and vegetables. Significance and Impact of the Study: The marine yeast R. paludigenum combined with CaCl₂ has greatly potential use as an alternative to chemical fungicides in inhibiting postharvest decay on cherry tomatoes.     

Heterozygote excess in a self-incompatible and partially clonal forest tree species -- Prunus avium L

Wild cherry (Prunus avium L.), a partially asexual self-incompatible forest tree, shows heterozygote excess, which is a poorly studied phenomenon. In three natural populations, we found significant heterozygote excess at almost all investigated loci (eight microsatellites and markers for the self-incompatibility locus). We examined four hypotheses to account for this observed heterozygote excess. First, negative F(IS) can result from a lack of selfed progeny in small populations of outcrossing species. A second explanation for negative F(IS) is selection during the life cycle of the most heterozygous individuals. A third explanation is negative assortative mating when reproduction occurs between individuals bearing phenotypes more dissimilar than by chance. The last explanation for negative F(IS) relies on asexual reproduction. Expectations for each hypothesis were tested using empirical data. Patterns of F(IS) differed among loci. Nevertheless, our experimental results did not confirm the small sample size hypothesis. Although one locus is probably under a hitch-hiking effect from the SI locus, we rejected the effect of the self-incompatibility locus for the genome as a whole. Similarly, although one locus showed a clear pattern consistent with the selection of heterozygous individuals, the heterosis effect over the whole genome was rejected. Finally, our results revealed that clonality probably explains significant negative F(IS) in wild cherry populations when considering all individuals. More theoretical effort is needed to develop expectations and hypotheses, and test them in the case of species combining self-incompatibility and partially asexual reproduction.     

The importance of electrostatic potential in the interaction of sweet proteins with the sweet taste receptor

In addition to many small molecular mass sweeteners there are in nature a few sweet proteins. The molecular volume of sweet proteins is so different from that of common sweeteners that it was difficult to understand how molecules as large as proteins can activate a receptor designed to host small molecules. We have recently shown that sweet proteins can activate the sweet receptor by a mechanism of interaction, called 'wedge model", in which proteins fit a large cavity of the receptor with wedge-shaped surfaces of their structures. In order to substantiate this model we have designed, expressed and characterized seven mutants of MNEI, a single chain monellin. Three uncharged residues of the interaction surface, Met42, Tyr63 and Tyr65, were changed either into acidic or basic residues whereas Asp68, a key acidic residue, was changed into a basic one. As a general trend, we observe that an increase of the negative charge is much more detrimental for sweetness than an increase of positive charge. In addition we show that by a careful choice of a residue at the center of the interface between MNEI and receptor, it is possible even to increase the sweetness of MNEI. These results are fully consistent with the wedge model.     

NaCl胁迫加重强光胁迫下超大甜椒叶片的光系统II和光系统I的光抑制

快速叶绿素荧光动力学可以在无损情况下探知叶片光合机构的损伤程度, 快速叶绿素荧光测定和分析技术(JIP-test)将测量值转化为多种具有生物学意义的参数, 因而被广泛应用于植物光合机构对环境的响应机制研究。该文研究了超大甜椒(Capsicum annuum)幼苗在强光及不同NaCl浓度胁迫下的荧光响应情况。与单纯强光胁迫相比, NaCl胁迫引起了叶绿素荧光诱导曲线的明显改变, 光系统II (PSII)光抑制加重, 同时PSII反应中心和受体侧受到明显影响, 而且高NaCl浓度胁迫下PSII供体侧受伤害明显, 同时PSI反应中心活性(P700⁺)在盐胁迫下明显降低。这些结果表明, NaCl胁迫会增强强光对超大甜椒光系统的光抑制, 并且浓度越高抑制越明显, 但对PSI的抑制作用低于PSII。高NaCl浓度胁迫易对PSII供体侧造成破坏, 且PSI光抑制严重。     

Modeling of single-cell oil production under nitrogen-limited and substrate inhibition conditions

Sweet sorghum extract was used as substrate for lipid accumulation by the oleaginous fungus Mortierella isabellina in batch cultures. Various initial sugar (13–91 g/L) and nitrogen (100–785 mg/L) concentrations resulting in various C/N (43–53) ratios were tested. Oil accumulation ranged between 43% and 51% corresponding to oil production from 2.2 to 9.3 g/L. A detailed mathematical model was developed. This model is able to adequately predict biomass growth, lipid accumulation, and sugar and nitrogen consumption. The model assumes that fungus growth is inhibited at high sugar concentrations. A set of kinetic experiments was used for model kinetic parameters estimation, while another set of experiments was used for model validation. The developed model could be generalized for similar systems of lipid accumulation and become a useful tool for reactor design for biofuel production. Bioeng. 2011; 108:1049–1055. © 2010 Wiley Periodicals, Inc.     

甜樱桃植株不同冠层部位光合特性及果实品质的研究

在横断山北段台地选取5株甜樱桃植株,应用Li-6400XP光合测定系统和用CI-700AB/HR2000光纤光谱仪研究其不同植株冠层部位对生理辐射光谱、光合特性及果实品质的影响。结果表明:(1)甜樱桃树冠下层和内部表观量子效率(α)最高,且光补偿点(LCP)最低,对弱光的利用能力强,而在树冠上层和外层光饱和点(LSP)极显著高于下层和内部,利用强光的能力强。(2)甜樱桃植株冠层的生理辐射由树冠的下层至上层、以及由内部至外部逐渐增强,短波光所占比例增大,说明甜樱桃对环境强光和相对弱光都具有一定的适应能力。(3)甜樱桃植株树冠上层叶片的最大光合速率(Pmax)、暗呼吸速率(Rd)、LCP和LSP均极显著高于下层,其光合同化以及代谢能力强;且生理辐射强、短波光多,利于甜樱桃果实可溶性固形物(TSS)、Vc及糖积累,但不利于有机酸积累。