Chemical compositions, larvicidal and antimicrobial activities of Zingiber castaneum (Škorničk. & Q.B. Nguyễn) and Zingiber nitens (M.F. Newman) essential oils

Abstract In this paper, the chemical constituents, larvicidal and antimicrobial activities of hydrodistilled essential oils from Zingiber castaneum Škorničk. & Q.B. Nguyễn and Zingiber nitens M.F. Newman were reported. The main constituents of Z. castaneum leaf were bicyclogermacrene (24.8%), germacrene D (12.9%), cis-β-elemene (11.2%) and β-pinene (10.3%), while sabinene (22.9%) and camphene (21.2%) were the significant compounds in the rhizome. However, the dominant compounds in the leaf of Z. nitens includes β-pinene (45.8%) and α-pinene (10.7%). Terpinen-4-ol (77.9%) was the most abundant compound of the rhizome. Z. castaneum rhizome oil displayed larvicidal activity against Aedes aegypti and Culex quinquefasciatus with LC50 values of 121.43 and 88.86 µg/mL, respectively, at 24 h. The leaf oil exhibited activity with LC50 values of 39.30 µg/mL and 84.97 µg/mL, respectively. Also, the leaf and rhizome oils of Z. nitens displayed greater larvicidal action towards Ae. aegypti with LC50 values of 17.58 µg/mL and 29.60 µg/mL, respectively. Only the rhizome oil displayed toxicity against Cx. quinquefasciatus with LC50 value of 64.18 µg/mL. All the studied essential oils inhibited the growth of Pseudomonas aeruginosa ATCC25923 with minimum inhibitory concentration (MIC) value of 50.0 µg/mL. This paper provides information on the larvicidal and antimicrobial potentials of Z. castaneum and Z. nitens essential oils.

RsmD, a Chloroplast rRNA m2G Methyltransferase, Plays a Role in Cold Stress Tolerance by Possibly Affecting Chloroplast Translation in Arabidopsis.

Ribosomal RNA (rRNA) methylation is a pivotal process in the assembly and activity of ribosomes, which in turn play vital roles in the growth, development and stress responses of plants. Although few methyltransferases responsible for rRNA methylation have been identified in plant chloroplasts, the nature and function of these enzymes in chloroplasts remain largely unknown. In this study, we characterized ArabidopsisRsmD (At3g28460), an ortholog of the methyltransferase responsible for N2-methylguanosine (m2G) modification of 16S rRNA in Escherichia coli. Confocal microscopic analysis of an RsmD- green fluorescent protein fusion protein revealed that RsmD is localized to chloroplasts. Primer extension analysis indicated that RsmD is responsible for m2G methylation at position 915 in the 16S rRNA of Arabidopsis chloroplasts. Under cold stress, rsmd mutant plants exhibited retarded growth, i.e. had shorter roots, lower fresh weight and pale-green leaves, compared with wild-type (WT) plants. However, these phenotypes were not detected in response to drought or salt stress. Notably, the rsmd mutant was hypersensitive to erythromycin or lincomycin and accumulated fewer chloroplast proteins compared with the WT, suggesting that RsmD influences translation in chloroplasts. Complementation lines expressing RsmD in the rsmd mutant background recovered WT phenotypes. Importantly, RsmD harbored RNA methyltransferase activity. Collectively, the findings of this study indicate that RsmD is a chloroplast 16S rRNA methyltransferase responsible for m2G915 modification that plays a role in the adaptation of Arabidopsisto cold stress.

Essential Oils of Zingiber Species from Vietnam: Chemical Compositions and Biological Activities.

Mosquito-borne diseases are a large problem in Vietnam as elsewhere. Due to environmental concerns regarding the use of synthetic insecticides as well as developing insecticidal resistance, there is a need for environmentally-benign alternative mosquito control agents. In addition, resistance of pathogenic microorganisms to antibiotics is an increasing problem. As part of a program to identify essential oils as alternative larvicidal and antimicrobial agents, the leaf, stem, and rhizome essential oils of several Zingiber species, obtained from wild-growing specimens in northern Vietnam, were acquired by hydrodistillation and investigated using gas chromatography. The mosquito larvicidal activities of the essential oils were assessed against Culex quinquefasciatus, Aedes albopictus, and Ae. aegypti, and for antibacterial activity against a selection of Gram-positive and Gram-negative bacteria, and for activity against Candida albicans. Zingiber essential oils rich in α-pinene and ß-pinene showed the best larvicidal activity. Zingiber nudicarpum rhizome essential oil showed excellent antibacterial activity against Enterococcus faecalis, Staphylococcus aureus, and Bacillus cereus, with minimum inhibitory concentrations (MIC) of 2, 8, and 1 µg/mL, respectively. However, the major components, α-pinene and ß-pinene, cannot explain the antibacterial activities obtained.

Functional Characterization of a Putative RNA Demethylase ALKBH6 in Arabidopsis Growth and Abiotic Stress Responses.

RNA methylation and demethylation, which is mediated by RNA methyltransferases (referred to as "writers") and demethylases (referred to as "erasers"), respectively, are emerging as a key regulatory process in plant development and stress responses. Although several studies have shown that AlkB homolog (ALKBH) proteins are potential RNA demethylases, the function of most ALKBHs is yet to be determined. The Arabidopsis thaliana genome contains thirteen genes encoding ALKBH proteins, the functions of which are largely unknown. In this study, we characterized the function of a potential eraser protein, ALKBH6 (At4g20350), during seed germination and seedling growth in Arabidopsis under abiotic stresses. The seeds of T-DNA insertion alkbh6 knockdown mutants germinated faster than the wild-type seeds under cold, salt, or abscisic acid (ABA) treatment conditions but not under dehydration stress conditions. Although no differences in seedling and root growth were observed between the alkbh6 mutant and wild-type under normal conditions, the alkbh6 mutant showed a much lower survival rate than the wild-type under salt, drought, or heat stress. Cotyledon greening of the alkbh6 mutants was much higher than that of the wild-type upon ABA application. Moreover, the transcript levels of ABA signaling-related genes, including ABI3 and ABI4, were down-regulated in the alkbh6 mutant compared to wild-type plants. Importantly, the ALKBH6 protein had an ability to bind to both m6A-labeled and m5C-labeled RNAs. Collectively, these results indicate that the potential eraser ALKBH6 plays important roles in seed germination, seedling growth, and survival of Arabidopsis under abiotic stresses.