Biodegradation of phytane (2,6,10,14-tetramethylhexadecane) and accumulation of related isoprenoid wax esters by Mycobacterium ratisbonense strain SD4 under nitrogen-starved conditions

The accumulation of storage lipids during the biodegradation of 2,6,10,14-tetramethylhexadecane (phytane) by Mycobacterium ratisbonense strain SD4 grown under nitrogen-starved conditions was investigated. Detailed chemical analysis of intracellular metabolites revealed the existence of (at least) three different pathways for the catabolism of phytane, and the accumulation of significant proportions (39% of the total lipids) of several isoprenoid wax esters formed by condensation of oxidation products of the hydrocarbon. In contrast, triacylglycerols but no wax esters were accumulated by strain SD4 grown on hexadecane, the unbranched homologue of phytane.     

两种吹绵蚧蜡泌物超微结构的研究

采用扫描电镜技术研究了澳洲吹绵蚧lcerya purchase Maskell和埃及吹绵蚧Icerya aegyptiaca(Douglas)不同龄期主要泌蜡腺体和蜡泌物的超微结构.结果发现:成虫期背面的丝状蜡是由多格腺和皮毛共同分泌产生的.卵囊是由雌成虫成熟时腹部腹面的半圆形卵囊带所分泌的,也是实心丝状蜡结构.若虫期吹绵蚧背面覆盖着由多格腺分泌的丝状蜡,实心结构;腹面有长丝状的蜡质缠绕,紧贴腹面体壁的还有一层小蜡圈.     

Interacting elevated CO2 and tropospheric O3 predisposes aspen (Populus tremuloides Michx.) to infection by rust (Melampsora medusae f. sp. tremuloidae)

We investigated the interaction of elevated CO₂ and/or (Ozone) O₃ on the occurrence and severity of aspen leaf rust (Melampsora medusae Thuem. f. sp. tremuloidae) on trembling aspen (Populus tremuloides Michx.). Furthermore, we examined the role of changes in leaf surface properties induced by elevated CO₂ and/or O₃ in this host–pathogen interaction. Three‐ to five‐fold increases in levels of rust infection index were found in 2 consecutive years following growing‐season‐long exposures with either O₃ alone or CO₂ + O₃ depending on aspen clone. Examination of leaf surface properties (wax appearance, wax amount, wax chemical composition, leaf surface and wettability) suggested significant effects by O₃ and CO₂ + O₃. We conclude that elevated O₃ is altering aspen leaf surfaces in such a way that it is likely predisposing the plants to increased infection by aspen leaf rust.     

Effect of drought on phytyl wax esters in Phaseolus leaves

The small amount of phytol which is bound as wax ester in mature bean leaves is increased 10–20 fold by drought. Watering the plants before permanent wilt reverses this trend. Maximum amounts of phytyl wax esters in plants still viable are higher in the drought resistant tepary bean (Phaseolus acutifolius) than in the less resistant garden bean (P. vulgaris).     

Leaf Epidermal Cells： A Trap for Lipophilic Xenobiotics

Plant surfaces are covered by a layer of cuticle, which functions as a natural barrier to protect plants from mechanical damage, desiccation, and microbial invasion. Results presented in this report show that the epicuticular wax and the cuticle of plant leaves also play an important role in resisting xenobiotic invasion. Although the epicuticular wax is impermeable to hydrophilic xenobiotics, the cuticle not only restricts the penetration of hydrophilic compounds into leaf cells, but also traps lipophilic ones. The role of the epidermal cells of plant leaves in resisting xenobiotic invasion has been neglected until now. The present study shows, for the first time, that the epidermal cells may reduce or retard the transport of lipophilic xenobiotics into the internal tissues through vacuolar sequestration. Although the guard cells appear to be an easy point of entry for xenobiotics, only a very small proportion of xenobiotics present on the leaf surface actually moves into leaf tissues via the guard cells .     

Antimicrobial activity in the egg wax of the African cattle tick Amblyomma hebraeum (Acari: Ixodidae)

Eggs of the tick Amblyomma hebraeum Koch (Acari: Ixodidae) inhibited the growth of Escherichia coli and Serratia marcescens (Gram-negative bacteria) in solid culture, but not the growth of Staphylococcus epidermidis, and only marginally the growth of Bacillus subtilis (Gram-positive bacteria). When egg wax was extracted with chloroform/methanol (2:1), the extract contained antibacterial activity, but the denuded eggs did not. When assayed against bacteria in liquid culture, the aqueous phase inhibited the growth of S. epidermidis. However, the activity against E. coli was lost during extraction. The antimicrobial component of the aqueous phase was heat stable (100°C for 10 min), resistant to proteinase K (15 min at 55°C) and to pronase (30 min at 37°C). The antibacterial activity in the aqueous phase increased the permeability of the cell membrane of susceptible bacterial cells within 30 min. However, lysis of the cells was detected by optical density measurements (OD_{600 nm}) only after 1.5 h. The most evident cytological changes observed by transmission electron microscopy were a thickening of the cell wall and the appearance of numerous electron lucent areas within the cytoplasm of treated bacteria. Gené’s organ, the egg-waxing organ in ticks, grew enormously during the first 16 days post-engorgement, and gained antimicrobial activity by day 10 (when oviposition began). This suggests that Gené’s organ is the major source of the antibacterial substance in the egg wax. The vitellogenic hormone in A. hebraeum, 20-hydroxyecdysone, when injected into recently engorged females, did not stimulate growth of Gené’s organ or precocious secretion of antimicrobial activity.     

Hydrogen isotopic compositions of n-alkanes from terrestrial plants correlate with their ecological life forms

Stable hydrogen isotopic compositions (δD) of compound-specific biomarkers, such as n-alkanes from plant leaf waxes, can be used as a proxy for paleoclimatic change. However, the relationship between hydrogen isotopes of plant leaf wax and plant ecological life forms is not well understood. Here, we report the δD of n-alkanes from 34 modern terrestrial plants, including twenty-one C₃ plants and thirteen C₄ plants from northwestern China, determined using gas chromatography/thermal conversion/isotope ratio mass spectrometry. Our data show that the stable hydrogen isotopes are poorly correlated with the plant photosynthetic pathway (C₃ vs. C₄) and that they do not give clear regional precipitation signals. Together with a comparative analysis of published δD values from plant leaf waxes in other regions, we believe that the stable hydrogen isotope of plant leaf waxes is more closely related to ecological life forms of these terrestrial plants (i.e. tree, shrub, and grass). In general, the grasses have more negative δD values than the co-occurring trees and shrubs. Our findings suggest that the δD values of sedimentary leaf waxes from higher plants may record changes of a plant ecosystem under the influence of environmental alteration and imply that reconstruction of the paleoclimate using δD values from plant n-alkanes should be based upon specific plant taxa, and comparison should be made among plants with similar ecological life forms.     

蜡酯合成途径及关键酶的研究进展

蜡酯对于生物的生命活动具有重要意义,研究表明植物和动物的蜡酯合成存在保守途径。即脂酰辅酶A（fatty acyl-CoA）在脂酰辅酶A还原酶（fatty acyl-CoAreductase,FAR）的作用下还原成脂肪醇,脂肪醇和脂酰辅酶A在蜡酯合酶（wax synthase,WS）的作用下生成酯,FAR和WS是该途径的关键酶,这两个酶的结构和功能在不同物种之间表现出很大差异,目前对于这两个酶缺乏系统的归纳分析。该文综述了蜡酯合成途径及FAR和WS的序列特征、生化特性及参与的生理功能,分析了这两种酶相关研究存在的问题,旨在为昆虫的蜡酯合成研究提供参考。