植物化学通讯研究进展

 生物的信息传递是生命科学中引人入胜的研究领域之一,生物种间种内和个体内都存在着物理和化学等各种信息交流方式。植物种间种内是否通过物理信号进行通讯交流还是一个未知数,但邻近的同种或异种植物通过化学物质为媒介的通讯关系确是客观存在的。最近,愈来愈多的研究证明：许多陆生植物种可以合成并释放特定的次生物质,这些次生物质可以通过空气和土壤两种载体进行信息传递,尤其是在植物受到侵袭和寄生条件下。茉莉酮酸甲酯、水杨酸甲酯和乙烯等挥发性次生物质被确证为以空气为媒介进行植物种间和种内通讯的化学信号分子。植物根分泌的黄酮和氢醌等分子也可以经土壤媒介传递信息。由于在自然条件下植物根系分泌物的收集和活性信号分子的俘获及鉴定技术还未能突破,这增加了以土壤为媒介的植物种间和种内化学通讯关系研究的难度。但不论如何,植物的化学通讯是植物种间和种内交流的主要方式,植物间的化学通讯关系的研究还处于突破的前夜,这方面的任一研究成果都会引起世界性的关注。因此,破译植物种间和种内化学通讯密码具有重要的学术价值。     

Integration of Herbicides with Arthropod Biocontrol Agents for Weed Control

Classical biological control of weeds using arthropods is being attempted on a large scale in a number of countries, sometimes with spectacularly successful outcomes. However, in many cases biocontrol is not completely effective and use of herbicides on weeds continues to occur, either in the presence of biocontrol agents or as an alternative to them. The ways in which the two techniques may interact are discussed, including direct toxicity of herbicides to biocontrol agents, responses to death of host plants and responses to sublethal changes caused by herbicides with different modes of action. A literature review for selected weed taxa showed that the great majority of publications relate to either chemical or to biological control techniques separately, with integration of the two seldom addressed. Possible reasons for this situation are discussed and some suggestions for future priorities are made.     

Methyl palmitate: a novel product of the Medfly (Ceratitis capitata) corpus allatum

The corpus allatum (CA) of adult female Ceratitis capitata produces methyl palmitate (MP) in vitro, in addition to JHB₃ and JH III. Biosynthesized MP migrates on TLC and co-elutes from RP-18 HPLC with synthetic MP. Its identity is verified herein by GCMS. MP production is up-regulated twofold by mevastatin, an inhibitor of mevalonic acid-dependent isoprene biosynthesis. Fosmidomycin, an inhibitor of mevalonic acid-independent isoprene synthesis in graminaceous plants, up-regulates MP synthesis by about fourfold. However, it does not depress JHB₃ biosynthesis concurrently. This suggests that the initial enzyme(s) in the conversion of 1-deoxy-xylulose 5-phosphate to isoprene is presumably present in C. capitata, but is inhibited by fosmidomycin, and this inhibition diverts precursors to MP synthesis. Phytol, an acyclic diterpene, might be suppressing isoprene biosynthesis by CA, thereby resulting in a fourfold increase in the MP biosynthesis. Linolenic acid is an end-product and its presence in incubation media up-regulates MP biosynthesis by twofold, presumably due to the feedback diversion to biosynthesis of C_16:0 and its methyl ester. Biosynthesis of MP is markedly depressed after mating, while otherwise maintained at significantly higher levels in virgin females. MP biosynthesis is significantly reduced in virgin females by direct axonal control but is less consistent after mating.     

Elicitation of different Panax ginseng transformed root phenotypes for an improved ginsenoside production

We tested the effect of the presence in the culture medium of chitosan, vanadyl sulfate or methyl jasmonate on growth and ginsenoside production of three stable hairy root lines of Panax ginseng C.A. Meyer showing different morphological phenotypes C-M, HR-M and T-M. The response depended upon line phenotype, specificity of the elicitor and the stage of growth at which the lines were treated. The highest ginsenoside yield was found when methyl jasmonate was added during the progressive deceleration growth phase (on day 25 of culture). In this case, the ginsenoside content reached at the end of the culture (day 28) by root lines C-M, HR-M and T-M was, respectively, 2, 1.8 and 4 times higher than the highest content achieved, also at the end of the culture, by the corresponding untreated root lines. Under the same conditions, the ginsenoside content in the presence of vanadyl sulfate also increased considerably, while with chitosan it clearly decreased. The ginsenoside pattern in response to the presence of the elicitors is also considered.     

Synthesis of monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside for epitope mapping of anti-Candida albicans antibodies

A panel of six complementary monodeoxy and mono-O-methyl congeners of methyl β-d-mannopyranosyl-(1→2)-β-d-mannopyranoside (1) were synthesized by stereoselective glycosylation of monodeoxy and mono-O-methyl monosaccharide acceptors with a 2-O-acetyl-glucosyl trichloroacetimidate donor, followed by a two-step oxidation-reduction sequence at C-2′. The β-manno configurations of the final deprotected congeners 2-7 were confirmed by measurement of ¹J_C1,H1 heteronuclear and ³J_1′,2′ homonuclear coupling constants. These disaccharide derivatives will be used to map the protective epitope recognized by a protective anti-Candida albicans monoclonal antibody C3.1 (IgG3) and to determine its key polar contacts with the binding site.     

Effect of elicitors on the production of gossypol and methylated gossypol in cotton hairy roots

The effect of two chemical elicitors, salicylic acid and methyl jasmonate, on the production of gossypol, 6-methoxygossypol, and 6,6′-dimethoxygossypol in Gossypium barbadense hairy roots was examined. Methyl jasmonate, but not salicylic acid, was found to increase the production of gossypol and its methylated forms, but with a concomitant reduction in culture growth. The optimal methyl jasmonate dose was between 100 and 300 μM for hairy roots harvested 7 days after elicitation. After 20 d of induction with 100 μM methyl jasmonate, an eightfold increase in the level of gossypol was observed in elicited cultures compared with control cultures, double the highest gossypol levels previously reported for any cotton tissue. A two to threefold increase in the level of 6-methoxygossypol and a slight increase in the levels of 6,6′-dimethoxygossypol were also observed. Although methyl jasmonate stimulated the production of both optical forms of gossypol, the distribution of the enantiomers was different between elicited and control cultures.     

Two poplar methyl salicylate esterases display comparable biochemical properties but divergent expression patterns

Two genes encoding proteins of 98% sequence identity that are highly homologous to tobacco methyl salicylate (MeSA) esterase (SABP2) were identified and cloned from poplar. Proteins encoded by these two genes displayed specific esterase activities towards MeSA to produce salicylic acid, and are named PtSABP2-1 and PtSABP2-2, respectively. Recombinant PtSABP2-1 and PtSABP2-2 exhibited apparent Km values of 68.2 ± 3.8 μM and 24.6 ± 1 μM with MeSA, respectively. Structural modeling using the three-dimensional structure of tobacco SABP2 as a template indicated that the active sites of PtSABP2-1 and PtSABP2-2 were highly similar to that of tobacco SABP2. Under normal growing conditions, PtSABP2-1 showed the highest level of expression in leaves and PtSABP2-2 was most highly expressed in roots. In leaf tissues of poplar plants under stress conditions, the expression of PtSABP2-1 was significantly down-regulated by two stress factors, whereas the expression of PtSABP2-2 was significantly up-regulated by four stress factors. The plausible mechanisms leading to these two highly homologous MeSA esterase genes involved in divergent biological processes in poplar are discussed.     

Selective backbone labelling of ILV methyl labelled proteins

Adding the ¹³C labelled 2-keto-isovalerate and 2-oxobutanoate precursors to a minimal medium composed of ¹²C labelled glucose instead of the commonly used (²D, ¹³C) glucose leads not only to the ¹³C labelling of (I, L, V) methyls but also to the selective ¹³C labelling of the backbone C_α and CO carbons of the Ile and Val residues. As a result, the backbone (¹H, ¹⁵N) correlations of the Ile and Val residues and their next neighbours in the (i + 1) position can be selectively identified in HN(CA) and HN(CO) planes. The availability of a selective HSQC spectrum corresponding to the sole amide resonances of the Ile and Val residues allows connecting them to their corresponding methyls by the intra-residue NOE effect, and should therefore be applicable to larger systems.     

Biodiesel production via transesterification of palm olein using waste mud crab (Scylla serrata) shell as a heterogeneous catalyst

A recent rise in crab aquaculture activities has intensified the generation of waste shells. In the present study, the waste shells were utilized as a source of calcium oxide to transesterify palm olein into methyl esters (biodiesel). Characterization results revealed that the main component of the shell is calcium carbonate which transformed into calcium oxide when activated above 700 °C for 2 h. Parametric studies have been investigated and optimal conditions were found to be methanol/oil mass ratio, 0.5:1; catalyst amount, 5 wt.%; reaction temperature, 65 °C; and a stirring rate of 500 rpm. The waste catalyst performs equally well as laboratory CaO, thus creating another low-cost catalyst source for producing biodiesel. Reusability results confirmed that the prepared catalyst is able to be reemployed up to 11 times. Statistical analysis has been performed using a Central Composite Design to evaluate the contribution and performance of the parameters on biodiesel purity.     

Enzymatic conversion of sunflower oil to biodiesel in a solvent-free system: Process optimization and the immobilized system stability

The feasibility of using the commercial immobilized lipase from Candida antarctica (Novozyme 435) to synthesize biodiesel from sunflower oil in a solvent-free system has been proved. Using methanol as an acyl acceptor and the response surface methodology as an optimization technique, the optimal conditions for the transesterification has been found to be: 45 ^oC, 3% of enzyme based on oil weight, 3:1 methanol to oil molar ratio and with no added water in the system. Under these conditions, >99% of oil conversion to fatty acid methyl ester (FAME) has been achieved after 50 h of reaction, but the activity of the immobilized lipase decreased markedly over the course of repeated runs. In order to improve the enzyme stability, several alternative acyl acceptors have been tested for biodiesel production under solvent-free conditions. The use of methyl acetate seems to be of great interest, resulting in high FAME yield (95.65%) and increasing the half-life of the immobilized lipase by about 20.1 times as compared to methanol. The reaction has also been verified in the industrially feasible reaction system including both a batch stirred tank reactor and a packed bed reactor. Although satisfactory performance in the batch stirred tank reactor has been achieved, the kinetics in a packed bed reactor system seems to have a slightly better profile (93.6 ± 3.75% FAME yield after 8–10 h), corresponding to the volumetric productivity of 48.5 g/(dm³ h). The packed bed reactor has operated for up to 72 h with almost no loss in productivity, implying that the proposed process and the immobilized system could provide a promising solution for the biodiesel synthesis at the industrial scale.