Plant Chemical Defense Induced by a Seed-Eating Pollinator Mutualist

Plant-seed parasite pollination mutualisms involve a specific pollinator whose larvae develop by consuming a fraction of the host plant seeds. These mutualisms are stable only if the plant can control seed destruction by the larvae. Here, we studied the chemical response of the European globeflower Trollius europaeus to infestation by an increasing number of Chiastocheta fly larvae. We used liquid chromatographic analysis to compare the content of phenolic compounds in unparasitized and parasitized fruits collected in two natural populations of the French Alps, and mass spectrometry and nuclear magnetic resonance to elucidate the structure of adonivernith, a C-glycosyl-flavone. This compound is present in many of the organs of T. europaeus, but not found in other Trollius species. Furthermore, it is overproduced in the carpel walls of parasitized fruits, and this induced response to infestation by fly larvae is density-dependent (increases with larval number), and site-dependent (more pronounced in the high-altitude site). Mechanical damage did not induce adonivernith production. This tissue-specific and density-dependent response of T. europaeus to infestation by Chiastocheta larvae might be an efficient regulation mechanism of seed-predator mutualist population growth if it decreases survival or growth of the larvae.     

“北京798”的“2010艺术空间”设计中空树形结构在中国现实条件下的多维度实践

今天的“北京798”正处于从单纯的艺术区向城市文化旅游区的演变之中,在798核心区里的新建项目“2010艺术空间”引发了作者对798艺术与商业的未来关系的思考。作者用“7983．0”这个概念描述了艺术与商业异质共生的内在联系,并把这种差异性互补的内在联系结合对现场条件及现实功能的回应,演化为一种单一连续的中空树形结构。单一连续的中空使结构产生了内外关系,对内形成艺术空间,对外形成商业空间;从真实结构上看,艺术支撑着商业,从现实运作上看,商业支撑着艺术：树形同时具有的聚或散两种几何关系,使得空间既不是完全的离散化,也不是完全的向心性,而是两者在某种趋势性方向上形成的聚合。建筑师发现了这个结构可能具有的原型潜力,因此,这个个案研究就成为了中空树形结构在中国现实条件下的一次多维度实践,既是回应798艺术与商业现实的关系,也是研究这种结构在构成逻辑、采光、尺度、功能、事件等多重维度上构成     

The Role of Extrafloral Nectar Amino Acids for the Preferences of Facultative and Obligate Ant Mutualists

Plants in some 300 genera produce extrafloral nectar (EFN) to attract ants as a means of indirect defence. Among Mesoamerican Acacia species, obligate myrmecophytes produce EFN constitutively to nourish symbiotic ant mutualists, while non-myrmecophytes induce EFN secretion in response to herbivore damage to attract non-symbiotic ants. Since symbiotic Acacia ants entirely depend on the host-derived food rewards while non-symbiotic ants need to be attracted to EFN, this system allows comparative analyses of the function of EFN components in ant nutrition and attraction. We investigated sugar and amino acid (AA) composition in EFN of two myrmecophytes (Acacia cornigera and Acacia hindsii) and two related non-myrmecophyte species (Acacia farnesiana and Prosopis juliflora). AA composition allowed a grouping of myrmecophytes vs. non-myrmecophytes. Behavioural assays with obligate Acacia inhabitants (Pseudomyrmex ferrugineus) and non-symbiotic ants showed that AA composition affected ant preferences at high but not at low AA/sugar ratios. Most interestingly, behavioural responses differed between the two types of ants tested: Symbiotic ants showed a clear preference for higher AA concentrations and preferred nectar mimics with those four AAs that most significantly characterised the specific nectar of their Acacia host plant. In contrast, non-symbiotic ants distinguished among nectars containing different sugars and between solutions with and without AAs but neither among nectars with different AA/sugar ratios nor among mimics containing different numbers of AAs. Our results confirm that both AAs and sugars contribute to the taste and attractiveness of nectars and demonstrate that the responses of ants to specific nectar components depend on their life style. AAs are a chemical EFN component that likely can shape the structure of ant–plant mutualisms.     

Role of Rhizobium,a plant growth promoting bacterium,in enhancing algal biomass through mutualistic interaction

Rhizobium plays the pivotal role in mutualistic interactions with plants and this study extends this mutualism to several species of green algae. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library experiments of Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus sp., and Botryococcus braunii revealed that the dominant phycosphere bacteria hosted by these green algae were Rhizobium, Mesorhizobium, and Shinella within Rhizobiales, Flavobacterium within Flavobacteriales, and Pseudomonas within Pseudomonadales. When Rhizobium sp., most prevalent and dominant bacterium isolated from C. vulgaris, was co-cultured with green algae, it promoted algal cell count by ∼72%. The qPCR analysis of 16S rRNA, Rhizobium specific rirA and rhtA genes, performed to understand the effect of green algae on growth of Rhizobium sp., showed a significant increase in copy numbers indicating sustained growth of Rhizobium upon co-culture with green algae. Likewise, growth rates of algae and Rhizobium increased by an average of ∼11% and ∼110%, respectively, confirming mutualistic interaction. Considering the presence of Rhizobium sp. in a variety of green algae, this must be a major mutualistic relationship among green algae and this ubiquitous association might serve as a model for elucidating the mutualistic mechanism between green algae and rhizobacter. This interaction could be also utilized in enhancing microalgal biomass, especially slow growing organisms like B. braunii, to augment their bioenergy productivity.     

Metabolic activity and symbiotic interactions of lactic acid bacteria and yeasts isolated from water kefir

Water kefir is a mildly sour and alcoholic drink fermented by a stable microbial multispecies community. With its high sugar content and low amino acid concentration water kefir medium represents a demanding habitat. In this ecological niche only well adapted microorganisms which are fit to the consortium are able to grow and mutually provide essential nutrients. The synergism between main representatives of water kefir yeasts and lactobacilli was studied in a co-culture model system. Co-cultivation of yeasts and lactobacilli in water kefir medium significantly increased cell yield of all interaction partners, delineating the interaction of these water kefir isolates as mutualism. The support of Zygotorulaspora (Z.) florentina was due to the acidification of the medium by the lactobacilli, whereas lactobacilli are improved in growth by the disposal of essential nutrients produced by yeasts. The trophic interaction between Lactobacillus (Lb.) hordei and yeasts is constituted by the release of amino acids and Vitamin B₆ from yeasts, whereas Lb. nagelii is supported in growth by their production of amino acids. The interaction of Z. florentina and Lb. nagelii was further examined to reveal that co-cultivation induced the yeast to release arginine, which was essential for Lb. nagelii.