PRODUCTION OF SECONDARY METABOLITES BY FILAMENTOUS TROPICAL MARINE CYANOBACTERIA: ECOLOGICAL FUNCTIONS OF THE COMPOUNDS

Cyanobacterial blooms are becoming more common in many reef habitats. The broadly acting feeding deterrent compound ypaoamide, produced by a mixed cyanobacterial assemblage, has been linked to bloom formation and mass fish die-offs ( Siganus argenteus and Siganus spinus ) in Guam. Specific metabolites produced by Lyngbya majuscula Gomont act as both feeding attractants to the specialist herbivore Stylocheilus longicauda , and as effective feeding deterrents to generalist fishes. Two-dimensional TLC (2D-TLC) analysis of cyanobacterial crude extracts was used to select chemically distinct populations (chemotypes) of bloom-forming filamentous cyanobacteria for chemical and ecological evaluation. Crude extracts produced by different species, chemotypes, and chemically distinct Micronesian marine cyanobacterial assemblages deter feeding activity of generalist reef herbivores. The ecological function of cyanobacterial secondary metabolites, especially as related to diversity of compound production and the relationship of metabolite production to bloom formation is discussed.     

Enhanced salidroside production in liquid-cultivated compact callus aggregates of Rhodiola sachalinensis: manipulation of plant growth regulators and sucrose

Liquid-cultivated compact callus aggregates (CCA) of Rhodiola sachalinensis were initiated from the explant of stems. Microscopic analysis showed that CCA displayed some level of cellular/tissue differentiation, which was perhaps responsible for the increased salidroside production. A higher ratio of cytokinin/auxin was found to be beneficial both for CCA growth and salidroside accumulation. Sucrose (> 100 g l-1) had a positive effect on salidroside synthesis, which was not due to an osmotic effect of the medium. The medium containing 40 g l-1 sucrose, 1.5 μM naphthaleneacetic acid and 15 μM 6-benzylaminopurine yielded ca. 120 mg l-1 salidroside after 24 days of culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen metabolism in cultured cotyledon explants of Pinus radiata during de novo organogenesis

Nitrogen metabolism was investigated under shoot-forming (SF) and non-shoot-forming (NSF) conditions in cultured cotyledon explants of Pinus radiata by following the incorporation of [¹⁴C]-l,2-acetate into various metabolites. Early in culture, the lipid fraction contained the most ¹⁴C; however, this percentage decreased in favor of increased label in the amphoteric fraction. Label in the amphoteric fraction of SF cultures decreased by day 21 but plateaued in NSF cultures at this time. Radioactive labeling of the principle nitrogen metabolites, glutamate and glutamine, which made up the majority of the amphoteric fraction, paralleled labeling patterns in the amphoteric fraction. Percentage label in glutamate remained at similar levels throughout the 21-day culture period for both SF and NSF cultures. Specific activity of glutamate (kBq mg^-1) was significantly greater during promeristemoid formation in SF compared to that in NSF tissues. Glutamine labeling increased during shoot bud initiation in SF cultures, but dropped to lower levels during shoot bud development. In contrast, in NSF cultures, there was a continual and substantial increase in glutamine labeling throughout the 21-day culture period. These trends were similar when the specific activities of glutamine were determined, as there was a continual decrease from culture initiation to the end of shoot bud differentiation in SF cultures. In NSF cultures, in contrast, specific activity of glutamine increased substantially from day 5 to 21 relative to that in SF cultures. The nitrogen assimilation enzymes glutamate synthase and glutamine synthase increased in activity from day 0 to 21 for both SF and NSF tissues. Enzyme activities for glutamate dehydrogenase were similar in both treatments to day 10 in culture but subsequently diverged, with activities in NSF cultures being substantially greater than those of SF cultures by day 21. Taken together, labeling and enzyme data indicate that nitrogen metabolism is enhanced during culture, especially in SF tissues at the time of promeristemoid formation, and in non-organ-forming tissue senescence-like metabolism was exhibited later in culture.     

Production,partial purification and bioassay of toxic metabolites of three plant pathogenic species ofColletotrichum in Nigeria

Colletotrichum lindemuthianum, C. truncatum andC. graminicola, produced metabolites in culture which induced necrotic lesions on susceptible hosts. The highest production was obtained from Richard's medium under shake incubation. The toxic metabolites of these pathogens fluoresce at 254 nm and 366 nm under ultraviolet light. The crude metabolites of theseColletotrichum species inhibited seed germination at the concentration of 100 µg/ml while the potency of the metabolites decreases with increase in dilution to 0.1 µg/ml. Similarly, the metabolites also inhibited growth of seedlings of hosts to the pathogen at 100 µg/ml and the potency again reduced with increasing dilution to 0.10 µg/ml.     

Regulation of photosynthetic carbon assimilation in leaves of C3–C4 intermediate species ofMoricandia andFlaveria

The relationship between the gas-exchange characteristics, the contents of photosynthetic intermediates and the quantum yield of photosystem II was examined at different intercellular partial pressures of CO₂ (p _i) in attached leaves of Moricandia arvensis L. (D.C.) and Flaveria floridana J.R. Johnson (both C₃–C₄ intermediate plants) and, for comparison, in F. pringlei Gandoger (a C₃ plant) and in F. bidentis (a C₄ plant). Both C₃–C₄ intermediate species had pools of phosphoenolpyruvate, pyruvate, alanine and aspartate intermediate to those of the C₃ and C₄ species examined. Moricandia arvensis had large pools of glycine at low p _i, consistent with the operation of a glycine shuttle from mesophyll to bundle-sheath cells. It also had a high pool of triose-phosphate at ambient partial pressures of CO₂, indicating that a glycerate-3-phosphate/triose-phosphate shuttle could operate in this species. This was not the case in F. floridana. A decline in the ribulose-1,5-bisphosphate and triose-phosphate pool in M. arvensis, and a rise in the pools of glycerate-3-phosphate and pyruvate in F. floridana, at low p _i, show different patterns of metabolic regulation in M. arvensis and F. floridana at low p _i in comparison to C₃ and C₄ plants.Abbreviations Frul,6bisP fructose-1,6-bisphosphate - PEP phosphoenolpyruvate PGA-glycerate-3-phosphate - p _i intercelular CO₂ pressure - PPFD photosynthetic photon flux density; - RuBP ribulose-1,5-bisphosphate - triose-P triose phosphates This work was done while R.C.L. was a Visiting Fellow at the Australian National University, and was sponsored by the Royal Society. We are grateful to Kathy Britt for assistance with the analysis of amino acids.     

谷胱甘肽的解毒作用与毒性代谢物

谷胱甘肽是细胞内重要的含SH基的非蛋白分子,它对氧自由基、有机氢过氧化物以及亲电子剂的灭活起着极重要的作用.但近年来的研究表明,一些连位二卤烷烃、卤烯烃、含酮结构的化合物以及一些异氰酸酯、异硫氰酸酯、醛、α,β－不饱和醛等与谷胱甘肽轭合后可导致毒性代谢物的形成.     

塔里木盆地胀果甘草内生放线菌多样性及抗菌活性分析

【目的】发掘具有开发前景的放线菌资源,对分离自新疆胀果甘草的内生放线菌的多样性、抗菌活性和次级代谢产物合成相关基因进行研究。【方法】采用5种培养基和3种前处理方法,从胀果甘草中分离获得80株放线菌。基于菌株形态学特征,对36株代表菌株进行抗菌活性检测,通过特异性引物扩增方法,检测了PKS I、PKS II、NPRS和卤化酶基因,探究其合成天然产物的潜在能力。结合筛选结果,选取其中20株代表菌,经16S r RNA基因测序,对其进行系统发育分析。【结果】培养基E2和E3结合热处理的分离效果较好;86.1%的代表菌株对供试的细菌、病原真菌表现出了不同程度的抗菌活性,PKS I、PKS II、NRPS基因和卤化酶基因阳性检出率分别为16.7%、72.2%、25.0%和11.1%。具有活性功能的代表菌株经16S r RNA基因测序分析,分别属于链霉菌属(Streptomyces)、小单胞菌属(Micromonospora)、红球菌属(Rhodococcus)和游动放线菌属(Actinoplanes)4个属,其中链霉菌属(Streptomyces)为优势菌属,占60%以上。【结论】胀果甘草是我国传统的药用植物,其植株内部蕴藏着丰富的放线菌资源,并在次生代谢产物合成方面拥有巨大潜力,具有进一步开发的价值。