Essential oils of some amazonian Mikania species

Terpenoid constituents were identified in the essential oils of Mikania banisteriae and M. congesta. M. amara contains aliphatic alcohols, aldehydes and acids besides p-cymene and thymol.     

An epoxygermacranolide and further constituents from Mikania species

Mikania purpurascens afforded in addition to known compounds a 5,10-epoxygermacranolide, while M. arrojadoi gave only known ent-kaurene derivatives.     

Compositae of the Guayana Highland—VII. Noteworthy species of Chromolaena and Mikania (Eupatorieae) from Venezuela

Chromolaena ternicapitulata is described from Sierra de Maigualida in T. F. Amazonas and a key to the species of Chromolaena from Guayana is given. Newly documented for the flora of Venezuela are M. aschersonii Hieron. and M. amazonica Baker, the second herein resurrected from the synonymy of common and widespread M. sprucei Baker. Mikania karsteniana Klot. ex Hieron. is not considered synonymous with M. pannosa Baker, thus the latter is again considered to be endemic to Guayana.     

Five mikanolide derivatives from mikania cynanchifolia and their biogenetic relationships

The investigation of the aerial parts of Mikania cynanchifolia afforded, in addition to miscandenin, five new sesquiterpene lactones, miscandenin-1,2-epoxide, an isomiscandenin and three further dilactones related to mikanolide. The structures of these new compounds were elucidated by high field ¹H NMR spectroscopy. The biogenetic relationships of the sesquiterpene lactones are briefly discussed.     

Cinnamoylgrandifloric acid from Mikania oblongifolia

Isolation of the cinnamate of grandifloric acid from Mikania oblongifolia is reported.     

Antimicrobial Constituents of the Leaves of Mikania micrantha H. B. K

Background

To isolate plant-derived compounds with antimicrobial activity from the leaves of Mikania micrantha, to determine the compounds configuration, and to evaluate their antimicrobial activity against eight plant pathogenic fungi (Exserohilum turcicum, Colletotrichum lagenarium, Pseudoperonispora cubensis, Botrytis cirerea, Rhizoctonia solani, Phytophthora parasitica, Fusarium solani, and Pythium aphanidermatum,) and four plant pathogenic bacteria (gram negative bacteria: Ralstonia dolaanacearum, Xanthomonas oryzae pv. Oryzae, Xanthomonas Campestris pv. Vesicatoria, and Xanthomonas campestris pv. Citri), and four bacteria (gram positive bacteria: Staphyloccocus aureus, Bacillus subtilis, Micrococcus luteus, and Bacillus cereus).

Methods and Results

Antimicrobial constituents of the leaves of M. micrantha were isolated using bioactivity- guided fractionation. The antifungal activity of the isolated compounds was evaluated by the inhibit hypha growth method and inhibit spore germination method. Characterization of antibacterial activity was carried out using the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs). MIC and MBC were determined by the broth microdilution method. Six compounds – deoxymikanolide, scandenolide, dihydroscandenolide, mikanolide, dihydromikanolide, and m - methoxy benzoic acid – have been isolated from leaves of Mikania micrantha H. B. K. Deoxymikanolide, scandenolide, and dihydroscandenolide were new compounds. The result of bioassay showed that all of isolated compounds were effective against tested strains and deoxymikanolide showed the strongest activity.

Conclusions and Significance

The leaves of M. micrantha may be a promising source in the search for new antimicrobial drugs due to its efficacy and the broadest range. Meanwhile, adverse impact of M. micrantha will be eliminated.     

Mikanokryptin,a new guianolide from Mikania

The isolation and structure determination of mikanokryptin, a stereoisomer of 11,13-dehydrogeigerin, from what appears to be a previously undescribed Mikania species is reported. Mikania micrantha HBK. yielded mikanolide and dihydromikanolide.     

Factors restraining parasitism of the invasive vine Mikania micrantha by the holoparasitic plant Cuscuta campestris

Mikania micrantha (Asteraceae) is one of the 10 most invasive weeds in the world and has caused tremendous economic and environmental losses in southern China. The dodder Cuscuta campestris (Convolvulaceae) is a native holoparasite that can parasitize and suppress M. micrantha, and thus is recommended as an effective control agent. However, the natural growth of dodder lags behind that of M. micrantha and fails to exert direct year-round suppression. To verify the effective parasitic distance, we placed a dodder seedling at a designated distance from the stem of M. micrantha and monitored coiling, haustorium formation, and survival. To verify suitable host stems for the parasite, we grew M. micrantha for more than 6 months to form stems of different sizes, taped dodder seedlings to the stems, and monitored. We used various temperatures to determine the effect on dodder seed germination and M. micrantha sprouting. The results showed that a dodder–host distance of 4 cm decreased the probability of successful parasitism to 0; dodder seedlings cannot parasitize M. micrantha stem diameters ≥0.3 cm; and the temperatures for the highest dodder seed germination and M. micrantha sprouting are 26 and 30 °C, respectively. We conclude that the lack of suitable M. micrantha parts within the dodder’s effective parasitism distance is the major cause of restricted dodder parasitism and that the lower temperature for the highest dodder germination compared to that for the highest M. micrantha sprouting may decrease the possibility of parasitism. To acquire aggressive parasitism, dodder should be manually assisted by dispersing its vegetative form.     

Ent-labdanes from Mikania alvimii

The aerial parts of Mikania alvimii afforded in addition to known compounds seven new ent-labdane derivatives and a 15-nor compound. The struct     

Germacranolides from Mikania grazielae

Mikania grazielae afforded two new germacranolides which were identified as 2α-acetoxyeupatolide and 2α-acetoxylaurenobiolide.     

Climbing capacity of the invasive vine Mikania micrantha Kunth on vertical artificial poles

Climbing capacity of invasive climbers is an important parameter to evaluate in the species invasive potential and processes in forests. However, this feature has not attracted the attention of invasion biologists. In the present study, we assessed the climbing traits and capacity of Mikania micrantha; a herbaceous invasive stem-twiner by supplying artificial vertical supports of different sizes ranging from 1.0 to 8.0 cm in diameter. We also calculated the theoretical maximum usable host size of a M. micrantha shoot based on confirm of the hypothesis that curvature of M. micrantha shoots will remain constant and not affected by support pole size. A total 164-tested M. micrantha shoots ascended the supports successfully. Shoot success rate declined significantly when support diameter exceeded 5.0 cm. The largest pole M. micrantha ascended successfully was 6.6 cm, while the theoretical value is 7.5 cm on average. Curvature declined significantly with increasing shoot diameter. However, no significant correlation was detected between curvature and support diameter, and most M. micrantha shoots maintained relatively constant curvature within a small fluctuation range (0.1–0.2 cm^?1) near the average value (0.16 cm^?1). We compared our results with the only two similar studies available, and concluded that climbing shoot ascent angle on supports decreased with increasing support diameter, while curvature remained constant, which was not affected by support size. These appear to be common attributes for herbaceous stem-twiners. Maximum usable host size was an important factor for successful M. micrantha ascent. We recommend this as a vital criterion in species management.     

Regeneration Capacity of Small Clonal Fragments of the Invasive Mikania micrantha H.B.K.: Effects of Burial Depth and Stolon Internode Length

The perennial stoloniferous herbaceous vine Mikania micrantha H.B.K. is among the most noxious exotic invaders in China and the world. Disturbance can fragment stolons of M. micrantha and disperse these fragments over long distances or bury them in soils at different depths. To test their regeneration capacity, single-node stolon fragments with stolon internode lengths of 0, 3, 6 and 12 cm were buried in soil at 0, 2, 5 and 8 cm depths, respectively. The fragments were growing for nine weeks, and their emergence status, growth and morphological traits were measured. The results indicated that increasing burial depth significantly decreased survival rate and increased the emergence time of the M. micrantha plants. At an 8-cm burial depth, very few fragments (2.19%) emerged and survived. Burial did not affect the total biomass and root to shoot ratio of the surviving M. micrantha plants that emerged from the 0- and 2-cm burial depths. Increasing internode length significantly increased survival rate and growth measures, but there was no interaction effect with burial depth for any traits measured. These results suggest that M. micrantha can regenerate from buried stolon fragments, and thus, disturbance may contribute to the spread of this exotic invader. Any human activities producing stolon fragments or facilitating dispersal should be avoided.     

4β,19-Epoxy-norkaurene and other diterpenes from Mikania banisteriae

The aerial parts of Mikania banisterae afforded four new diterpenes, ent-kaur-16-en-18-al, 18-acetoxy-ent-kaurene, 18-hydroxy-16α,17-epoxy-ent-kaurane and 4β-19-epoxy-18-nor-ent-kaurene.     

Books received

Chromolaena ternicapitulata is described from Sierra de Maigualida in T. F. Amazonas and a key to the species of Chromolaena from Guayana is given. Newly documented for the flora of Venezuela are M. aschersonii Hieron. and M. amazonica Baker, the second herein resurrected from the synonymy of common and widespread M. sprucei Baker. Mikania karsteniana Klot. ex Hieron. is not considered synonymous with M. pannosa Baker, thus the latter is again considered to be endemic to Guayana.     

Growth but Not Photosynthesis Response of a Host Plant to Infection by a Holoparasitic Plant Depends on Nitrogen Supply

Parasitic plants can adversely influence the growth of their hosts by removing resources and by affecting photosynthesis. Such negative effects depend on resource availability. However, at varied resource levels, to what extent the negative effects on growth are attributed to the effects on photosynthesis has not been well elucidated. Here, we examined the influence of nitrogen supply on the growth and photosynthesis responses of the host plant Mikania micrantha to infection by the holoparasite Cuscuta campestris by focusing on the interaction of nitrogen and infection. Mikania micrantha plants fertilized at 0.2, 1 and 5 mM nitrate were grown with and without C. campestris infection. We observed that the infection significantly reduced M. micrantha growth at each nitrate fertilization and more severely at low than at high nitrate. Such alleviation at high nitrate was largely attributed to a stronger influence of infection on root biomass at low than at high nitrate fertilization. However, although C. campestris altered allometry and inhibited host photosynthesis, the magnitude of the effects was independent of nitrate fertilizations. The infection reduced light saturation point, net photosynthesis at saturating irradiances, apparent quantum yield, CO₂ saturated rate of photosynthesis, carboxylation efficiency, the maximum carboxylation rate of Rubisco, and maximum light-saturated rate of electron transport_, and increased light compensation point in host leaves similarly across nitrate levels, corresponding to a similar magnitude of negative effects of the parasite on host leaf soluble protein and Rubisco concentrations, photosynthetic nitrogen use efficiency and stomatal conductance across nitrate concentrations. Thus, the more severe inhibition in host growth at low than at high nitrate supplies cannot be attributed to a greater parasite-induced reduction in host photosynthesis, but the result of a higher proportion of host resources transferred to the parasite at low than at high nitrate levels.     

Chromosome evolution in the genus Mikania (Compositae)

Karyotypic analysis of ten species of the genus Mikania was carried out using Feulgen staining. Species belonging to the following sections were analyzed: Section Thyrsigerae containing M. additicia (2n = 34), M. hemisphaerica, M. lanuginosa, and M. punctata (2n = 36), and Mikania sericea (2n = 42), which adds a new basic chromosome number (x = 21) to the genus and to the tribe Eupatorieae; Section Corymbosae with M. hastato-cordata (2n = 34) and M. involucrata and M. microptera with 2n = 36 chromosomes; Section Spicato-Racemosae with M. sessilifolia, with 2n = 108 chromosomes. One unidentified species with 2n = 34 chromosomes was also analyzed. All the species studied show one large pair of chromosomes with a secondary constriction in the middle region of the long arm. The morphology of this chromosome suggests that it can be considered as a cytological marker for the genus. Because of the distinctive inflorescence types found in the genus Mikania and the high frequency of species with x = 18, a correlation between morphological and chromosomal evolution is discussed. The present study suggests that the basic original chromosome number for the genus is x = 18, from which the others (x = 17, 19, 20, 21) have been derived by aneuploidy to form the observed aneuploid series.     

Essential oil and terpenoids of Mikania micrantha

Twenty-seven mainly terpenoid constituents were identified in the essential oil of Mikania micrantha whole plant. Higher terpenoids present in the same plant included two kaurene derivatives and taraxasterol.     

Diterpenes and sesquiterpene lactones from Mikania congesta

The chloroform extract of the aerial parts of Mikania congesta, afforded four new geranylnerol derivatives, new analogs of deoxyelephantopin, a new melampolide and several known compounds. Structures were elucidated by spectroscopic methods and chemical transformations.     

Priority effects and competition by a native species inhibit an invasive species and may assist restoration

Selecting native species for restoration is often done without proper ecological background, particularly with regard to how native and invasive species interact. Here, we provide insights suggesting that such information may greatly enhance restoration success. The performance of the native vine, Pueraria lobata, and that of the invasive bitter vine, Mikania micrantha, were investigated in South China to test how priority effects (timing and rate of germination and seedling growth) and competition (phytochemical effects and competitive ability) impact invasive plant performance. We found that, in the absence of competition, the germination rate of M. micrantha, but not of P. lobata, was significantly affected by light availability. P. lobata seedlings also performed better than those of M. micrantha during early growth phases. Under competition, negative phytochemical effects of P. lobata on M. micrantha were strong and we found M. micrantha to have lower performance when grown with P. lobata compared to when grown by itself. Relative interaction indexes indicated that, under interspecific competition, P. lobata negatively affected (i.e., inhibited) M. micrantha, whereas M. micrantha positively affected (i.e., facilitated) P. lobata. Higher photosynthetic efficiency and soil nutrient utilization put P. lobata at a further advantage over M. micrantha. Field trails corroborated these experimental findings, showing little recruitment of M. micrantha in previously invaded and cleared field plots that were sown with P. lobata. Thus, P. lobata is a promising candidate for ecological restoration and for reducing impacts of M. micrantha in China. This research illustrates that careful species selection may improve restoration outcomes, a finding that may also apply to other invaded ecosystems and species.