Phytochemistry Reviews (v.8, #3)
Introduction by Katarzyna Turnau (503-503).
Archaea in dry soil environments by Sari Timonen; Malin Bomberg (505-518).
Archaea belong to the least well known major group of soil inhabiting microbes as the concept of the very existence of the archaea was introduced only in 1977 and the domain of Archaea established in 1990. The first reports of finding these organisms in soils were published even later. This paper will review the research carried out of the archaea in dry moderate soil environments. It will particularly consider the specific habitats where the archaea live in soils, as well as their associations with other organisms. There is thus far relatively little knowledge about the metabolism of the soil archaea, but the knowledge about their exact habitats and associations as well as their genetic potential point the way to discovering more about the different soil archaeal functions.
Keywords: Crenarchaeota; Euryarchaeota; Filamentous fungi; Mycorrhiza; Rhizosphere
Host plant as an organizer of microbial evolution in the beneficial symbioses by Nikolai A. Provorov; Nikolai I. Vorobyov (519-534).
Evolution of beneficial plant–microbe symbioses is presented as a result of selective processes induced by hosts in the associated microbial populations. These processes ensure a success of “genuine mutualists” (which benefit the host, often at the expense of their own fitness) in competition with “symbiotic cheaters” (which consume the resources provided by host without expressing the beneficial traits). Using a mathematical model describing the cyclic microevolution of rhizobia–legume symbiosis, we suggest that the selective pressures in favor of N2-fixing (Fix+) strains operate within the in planta bacterial population due to preferential allocation of C resources into Fix+ nodules (positive partners’ feedbacks). Under the clonal infection of nodules, Fix+ strains (“genuine mutualists”) are supported by the group (inter-deme, kin) selection while under the mixed infections, this selection is ineffective since the Fix+ strains are over-competed by Fix− ones (“symbiotic cheaters”) in the nodular habitats. Nevertheless, under mixed infections, Fix+ strains may be supported due to the coevolutionary responses form plant population which induce the mutualism-specific types of natural (group, individual) selection including the frequency dependent selection implemented in rhizobia population during the competition for host infection. Using the model of multi-strain bacterial competition for inoculation of symbiotic (rhizospheric, nodular) habitats, we demonstrate that the individual selection in favor of host-specific mutualist genotypes is more intensive than in favor of non-host-specific genotypes correlating the experimental data on the coordinated increases of symbiotic efficiency and specificity in the rhizobia–legume coevolution. However, an overall efficiency of symbiotic system is maximal when the non-host-specific mutualists are present in rhizobia population, and selection in favor of these mutualists operating at the whole population level is of key importance for improving the symbiosis. Construction of the agronomically valuable plant–microbe systems should provide the optimization of host-specific versus non-host-specific mutualists’ composition in legume inoculants combined with the clonal penetration of these mutualists into the nodules.
Keywords: Biological altruism; Darwinian, frequency-dependent and group (inter-deme, kin) selection; Positive partners’ feedbacks; Rhizobia–legume symbiosis; Symbiotic N2 fixation
Metabolomics analysis of the Lolium perenne–Neotyphodium lolii symbiosis: more than just alkaloids? by Susanne Rasmussen; Anthony J. Parsons; Jonathan A. Newman (535-550).
Above ground plant parts of Lolium perenne often harbour endophytic Neotyphodium lolii fungi. These occur both naturally and commercially, as variant strains are introduced to modify the grass metabolic profile. They reside in the apoplastic spaces and rarely cause visible symptoms of infection. The vast majority of literature has focussed on the biosynthesis, accumulation, and ecological relevance of a limited number of alkaloids produced by N. lolii which have been shown to negatively affect insect pests and vertebrate herbivores. Much less is known about the effects of other metabolites in these interactions or the role of resource supply on metabolic profiles, nor critically on the metabolic consequences of differences in the amount (concentration) of endophyte present. Here, we provide a synthesis of some of our recently published studies on effects of resource supply (nitrogen, carbohydrates) on concentrations of endophytes and endophyte specific metabolites in the L. perenne–N. lolii association. We present results of both quantitative PCR and targeted metabolomics studies, using contrasting endophyte strains in two perennial ryegrass cultivars. We also present and discuss a hypothetical schematic representation of possible links between plant and fungal metabolic networks. A multiple regression analysis of numerical insect responses and metabolic profiles indicates that effects of endophyte infection on insect population sizes could be predicted by concentrations of a range of metabolites other than alkaloids and depended on insect species, fungal strain, and nitrogen supply.
Keywords: Ryegrass; Carbohydrates; Nitrogen; Herbivory; Metabolomics
Survival strategies of arbuscular mycorrhizal fungi in Cu-polluted environments by Nuria Ferrol; Manuel González-Guerrero; Ascensión Valderas; Karim Benabdellah; Concepción Azcón-Aguilar (551-559).
This review provides an overview of the mechanisms evolved by arbuscular mycorrhizal (AM) fungi to survive in Cu-contaminated environments. These mechanisms include avoidance strategies to restrict entry of toxic levels of Cu into their cytoplasm, intracellular complexation of the metal in the cytosol and compartmentalization strategies. Through the activity of specific metal transporters, the excess of Cu is translocated to subcellular compartments, mainly vacuoles, where it would cause less damage. At the level of the fungal colony, AM fungi have also evolved compartmentalization strategies based on the accumulation of Cu into specific fungal structures, such as extraradical spores and intraradical vesicles. In addition to the avoidance and compartmentalization strategies, AM fungi have also mechanisms to combat the Cu-generated oxidative stress or to repair the damage induced.
Keywords: Copper homeostasis; Copper tolerance; Glomalin; Glomus intraradices ; Oxidative stress alleviation
Intraspecific chemical variation within the crustose lichen genus Haematomma: anthraquinone production in selected cultured mycobionts as a response to stress and nutrient supply by Elfie Stocker-Wörgötter; Armin Hager; John A. Elix (561-569).
The mycobionts isolated from selected species of Haematomma (Haematomma africanum, Haematomma fenzlianum, Haematomma flourescens, Haematomma persoonii, Haematomma stevensiae) have been successfully cultured. The chemical profile of the mycobionts could be effectively influenced and modulated by varying the composition of the nutrient medium using alternative carbohydrates (glucose, sucrose, and polyols). Under artifical laboratory conditions and simulated environmental stress (exposure to UV light, desiccation, and lower temperatures) the mycobionts began producing typical secondary lichen metabolites after an incubation time of 5–6 months. Modified Lilly and Barnett medium (LBM) and Murashige Skoog Medium favoured the production of depsides such as sphaerophorin and isosphaeric acid. Surprisingly, the mycobiont from H. stevensiae in modified MS medium produced two anthraquinones in the mycelia, haematommone at the base and russulone in the upper parts of the mycelium. By contrast, the natural lichen only produced these anthraquinones in the reddish orange apothecia. The mycobiont from H. flourescens only produced the expected lichexanthone in LBM, enriched with the polyols, sorbitol and mannitol. Once the media requirements and environmental stress factors that trigger polyketide production in lichen mycobionts have been determined, it is possible to obtain a particular lichen product by a completely defined procedure. Using such knowledge, we should be able to study polyketide expression in mycobionts under optimized culture conditions for various genetic applications.
Keywords: Lichens; Secondary chemistry; Polyketides; Mycobiont cultures; Haematommone; Russulone
Medicinal plants as hosts of arbuscular mycorrhizal fungi and dark septate endophytes by Szymon Zubek; Janusz Błaszkowski (571-580).
Arbuscular mycorrhizal and dark septate endophyte associations of 31 medicinal plant species collected from the Garden of Medicinal Plants of the Faculty of Pharmacy, Jagiellonian University, Collegium Medicum in Kraków were investigated. Arbuscular mycorrhiza (AM) was found in 30 species; 23 were of the Arum-type, 5—Paris and 2 taxa revealed intermediate morphology. Many plants were strongly colonized by arbuscular mycorrhizal fungi (AMF). The mycelium of dark septate endophytes (DSE) was observed in 21 taxa. However, the percentage of root colonization by these fungi was low. Spores of 15 species of AMF (Glomeromycota) were found in the rhizosphere of the investigated plants. Our results are the first detailed report of both AMF and DSE associations of these plant species. The use of AMF and DSE during the process of medicinal plant cultivation for pharmaceutical purposes is discussed.
Keywords: Arbuscular mycorrhiza (AM); Cultivation; Dark septate endophytes (DSE); Glomeromycota; Medicinal plants
Guaianolides in apiaceae: perspectives on pharmacology and biosynthesis by Damian Paul Drew; Nadja Krichau; Kirsten Reichwald; Henrik Toft Simonsen (581-599).
The guaianolide group of sesquiterpene lactones contains a large number of compounds with biological activity. One of these guaianolides, thapsigargin from the genus Thapsia (Apiaceae), has been a subject of particular interest in recent years because of its ability to induce apoptosis, as the active part of a pro-drug, has produced promising results for the targeted treatment of prostate cancer. In this review, recent advances in understanding the biosynthetic pathway of sesquiterpenes in plants is described with a special emphasis on guaianolides, and a hypothetical pathway for the biosynthesis of thapsigargin is presented. Eighty-seven guaianolides from Apiaceae are presented. These compounds provide clues to possible enzymatic mechanisms generating the guaianolides in Apiaceae. Some of these 87 compounds have proven or might prove interesting with regards to their biological activity.
Keywords: Sesquiterpene lactones; Thapsigargin; SERCA inhibition
Azadirachta indica (neem): a plant of multiple biological and pharmacological activities by Sunday E. Atawodi; Joy C. Atawodi (601-620).
Azadirachta indica, commonly called neem or ‘dogonyaro’ in Nigeria, is a plant that has found varied use in ecological, medicinal and agricultural sectors. Biological and pharmacological activities attributed to different parts and extracts of these plants include antiplasmodial, antitrypanosomal, antioxidant, anticancer, antibacterial, antiviral, larvicidal and fungicidal activities. Others include antiulcer, spermicidal, anthelminthic, antidiabetic, anti-implantation, immunomodulating, molluscicidal, nematicidal, immunocontraceptive, insecticidal, antifeedant and insect repellant effects. But toxicological activities such as allergic, genotoxic, cytogenetic and radiosensitizing effects have also been reported in humans and some economic animals, particularly, aquatic organisms, chicks and goats. Bioassay-guided studies and phytochemical analyses utilizing modern state-of-the-art techniques such as HPLC–MS, GC–MS, NMR and Infra Red spectroscopy have revealed that phytocompounds like azadirachtins, nimocinol, isomeldenin, azadirachtol (a tetranortriterpernoid), 2,3′-dehydrosalanol gedunin, nimbin, nimolicinol, odoratone, azadironolide, isoazadironolide, naheedin and mahmoodin are responsible for the varied biological, pharmacological and toxicological properties observed. In this paper, we review how a developing country like Nigeria can harness the numerous opportunities presented by the multi-biological and multi-pharmacological nature of A. indica to solve some of her myriad problems, including those in the agricultural, health and economic sectors.
Keywords: Azadirachta indica ; Bioactive compounds; Biological activity; Neem; Pharmacological properties; Toxicological profile