Although the chronotoxicity of xenobiotics is relatively well known in mammals, the existence of daily rhythms of drug toxicity and effectiveness in fish has been neglected to date. The aim of this research was to investigate the influence of the time (middle of the light phase [ML] versus middle of the dark phase [MD]) of exposure to two anesthetic substances (MS-222 or clove oil) commonly used with fish on the median lethal concentration (LC(50)) and swimming activity of zebrafish (Danio rerio). To this end, adult zebrafish were kept under a 12 h:12 h light-dark (LD) cycle and exposed to different concentrations of the anesthetics for 15 min at ML or MD. LC(50) calculations were performed using the Spearman-Karber program, whereas swimming activity was video-recorded and analyzed with specialized software. Zebrafish exhibited a mostly diurnal activity pattern (77.9% of activity occurring during daytime). The acute toxicity and mortality caused by MS-222 and eugenol varied with the time of exposure. For MS-222, the LC(50) was 170.6 ± 7.4 mg/L in fish exposed at ML and 215.6 ± 3.9 mg/L at MD, whereas for eugenol the LC(50) was 70.3 ± 3.1 mg/L at ML and 104.9 ± 5.4 mg/L at MD. Exposure to sublethal concentrations of MS-222 and eugenol altered the swimming patterns of zebrafish in a different manner depending on the time of exposure. Thus, the time required for decreasing swimming activity during exposure to anesthetics was shorter at ML than at MD, whereas the recovery period was longer during the day. In conclusion, these results revealed that the toxicity and effectiveness of both anesthetic substances is highest during daytime, the active phase of fish, thus suggesting a link between the daily rhythms of behavior and toxicity.

The floral perianth, comprising sepals and petals, conceals the sexual organs and attracts pollinators. The coordination of growth and scent emission is not fully understood. We have analyzed the effect of knocking down CHANEL (PhCHL), the ZEITLUPE ortholog in petunia (PhCHL) by hairpin RNAs. Plants with low PhCHL mRNA had overall decreased size. Growth evaluation using time lapse image analysis showed that early leaf movement was not affected by RNAi:PhCHL, but flower angle movement was modified, moving earlier during the day in knockdown plants than in wild types. Despite differences in stem length, growth rate was not significantly affected by loss of PhCHL. In contrast, petal growth displayed lower growth rate in RNAi:PhCHL. Decreased levels of PhCHL caused strongly modified scent profiles, including changes in composition and timing of emission resulting in volatile profiles highly divergent from the wild type. Our results show a role of PhCHL in controlling growth and development of vegetative and reproductive organs in petunia. The different effects of PhCHL on organ development indicate an organ-specific interpretation of the down regulation of PhCHL. Through the control of both timing and quantitative volatile emissions, PhCHL appears to be a major coordinator of scent profiles.

BackgroundCowpea (Vigna unguiculata) is an important source of protein supply for animal and human nutrition. The major storage globulins VICILIN and LEGUMIN (LEG) are synthesized from several genes including LEGA, LEGB, LEGJ and CVC (CONVICILIN). The current hypothesis is that the plant circadian core clock genes are conserved in a wide array of species and that primary metabolism is to a large extent controlled by the plant circadian clock. Our aim was to investigate a possible link between gene expression of storage proteins and the circadian clock.ResultsWe identified cowpea orthologues of the core clock genes VunLHY, VunTOC1, VunGI and VunELF3, the protein storage genes VunLEG, VunLEGJ, and VunCVC as well as nine candidate reference genes used in RT-PCR. ELONGATION FACTOR 1-A (ELF1A) resulted the most suitable reference gene. The clock genes VunELF3, VunGI, VunTOC1 and VunLHY showed a rhythmic expression profile in leaves with a typical evening/night and morning/midday phased expression. The diel patterns were not completely robust and only VungGI and VungELF3 retained a rhythmic pattern under free running conditions of darkness. Under field conditions, rhythmicity and phasing apparently faded during early pod and seed development and was regained in ripening pods for VunTOC1 and VunLHY. Mature seeds showed a rhythmic expression of VunGI resembling leaf tissue under controlled growth chamber conditions. Comparing time windows during developmental stages we found that VunCVC and VunLEG were significantly down regulated during the night in mature pods as compared to intermediate ripe pods, while changes in seeds were non-significant due to high variance. The rhythmic expression under field conditions was lost under growth chamber conditions.ConclusionsThe core clock gene network is conserved in cowpea leaves showing a robust diel expression pattern except VunELF3 under growth chamber conditions. There appears to be a clock transcriptional reprogramming in pods and seeds compared to leaves. Storage protein deposition may be circadian regulated under field conditions but the strong environmental signals are not met under artificial growth conditions. Diel expression pattern in field conditions may result in better usage of energy for protein storage.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1244-2) contains supplementary material, which is available to authorized users.

The plant circadian clock controls a large number of internal processes, including growth and metabolism. Scent emission displays a circadian pattern in many species such as the snapdragon. Here we show that knocking down LATE ELONGATED HYPOCOTYL in Antirrhinum majus affects growth and scent emission. In order to gain an understanding of the growth kinetics, we took a phenomic approach using in-house artificial vision systems, obtaining time-lapse videos. Wild type flowers showed a higher growth speed than knockdown plants. The maximal growth rate was decreased by 22% in plants with lower LHY expression. Floral volatiles were differentially affected as RNAi plants showed advanced emission of compounds synthesized from cinnamic acid and delayed emission of metabolites of benzoic acid. The monoterpenes myrcene and ocimene were delayed, whereas the sesquiterpene farnesene was advanced. Overall, transgenic lines showed an altered volatile emission pattern and displayed a modified scent profile. Our results show that AmLHY plays an important role in the quantitative and qualitative control of floral growth and scent emission.

The plant circadian clock coordinates environmental signals with internal processes. We characterized the genomic and transcriptomic structure of the Petunia hybrida W115 clock in leaves and petals. We found three levels of evolutionary differences. First, PSEUDO-RESPONSE REGULATORS PhPRR5a, PhPRR5b, PhPRR7a, PhPRR7b, and GIGANTEA PhGI1 and PhGI2, differed in gene structure including exon number and deletions including the CCT domain of the PRR family. Second, leaves showed preferential day expression while petals tended to display night expression. Under continuous dark, most genes were delayed in leaves and petals. Importantly, photoperiod sensitivity of gene expression was tissue specific as TIMING OF CAB EXPRESSION PhNTOC1 was affected in leaves but not in petals, and PhPRR5b, PhPRR7b and the ZEITLUPE ortholog CHANEL, PhCHL, were modified in petals but not leaves. Third, we identified a strong transcriptional noise at different times of the day, and high robustness at dawn in leaves and dusk in petals, coinciding with the coordination of photosynthesis and scent emission. Our results indicate multilayered evolution of the Petunia clock including gene structure, number of genes and transcription patterns. The major transcriptional reprogramming of the clock in petals, with night expression may be involved in controlling scent emission in the dark.HighlightThe petunia leaf circadian clock shows maxima during the day while petal clock does it during the night. Reaction to dark is organ specific.