BackgroundThe circadian clock is an endogenous mechanism that coordinates biological processes with daily changes in the environment. In plants, circadian rhythms contribute to both agricultural productivity and evolutionary fitness. In barley, the photoperiod response regulator and flowering-time gene Ppd-H1 is orthologous to the Arabidopsis core-clock gene PRR7. However, relatively little is known about the role of Ppd-H1 and other components of the circadian clock in temperate crop species. In this study, we identified barley clock orthologs and tested the effects of natural genetic variation at Ppd-H1 on diurnal and circadian expression of clock and output genes from the photoperiod-response pathway.ResultsBarley clock orthologs HvCCA1, HvGI, HvPRR1, HvPRR37 (Ppd-H1), HvPRR73, HvPRR59 and HvPRR95 showed a high level of sequence similarity and conservation of diurnal and circadian expression patterns, when compared to Arabidopsis. The natural mutation at Ppd-H1 did not affect diurnal or circadian cycling of barley clock genes. However, the Ppd-H1 mutant was found to be arrhythmic under free-running conditions for the photoperiod-response genes HvCO1, HvCO2, and the MADS-box transcription factor and vernalization responsive gene Vrn-H1.ConclusionWe suggest that the described eudicot clock is largely conserved in the monocot barley. However, genetic differentiation within gene families and differences in the function of Ppd-H1 suggest evolutionary modification in the angiosperm clock. Our data indicates that natural variation at Ppd-H1 does not affect the expression level of clock genes, but controls photoperiodic output genes. Circadian control of Vrn-H1 in barley suggests that this vernalization responsive gene is also controlled by the photoperiod-response pathway. Structural and functional characterization of the barley circadian clock will set the basis for future studies of the adaptive significance of the circadian clock in Triticeae species.

The circadian clock is an important timing system that controls physiological responses to abiotic stresses in plants. However, there is little information on the effects of the clock on stress adaptation in important crops, like barley. In addition, we do not know how osmotic stress perceived at the roots affect the shoot circadian clock. Barley genotypes, carrying natural variation at the photoperiod response and clock genes Ppd-H1 and HvELF3, were grown under control and osmotic stress conditions to record changes in the diurnal expression of clock and stress-response genes and in physiological traits. Variation at HvELF3 affected the expression phase and shape of clock and stress-response genes, while variation at Ppd-H1 only affected the expression levels of stress genes. Osmotic stress up-regulated expression of clock and stress-response genes and advanced their expression peaks. Clock genes controlled the expression of stressresponse genes, but had minor effects on gas exchange and leaf transpiration. This study demonstrated that osmotic stress at the barley root altered clock gene expression in the shoot and acted as a spatial input signal into the clock. Unlike in Arabidopsis, barley primary assimilation was less controlled by the clock and more responsive to environmental perturbations, such as osmotic stress.

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Introduction Interest in essential oils was recently revived with their popularity increasing in medicine, pharmacy, and aromatherapy. This study was performed to identify the chemical compositions of the essential oil of Ruta chalepensis growing wildly in three regions in Palestine and to assess and compare their antimicrobial and antioxidant activities. Methods Identification of the essential oil was performed by gas chromatography coupled with mass spectrometry (GC-MS). Antimicrobial activity was tested against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Methicillin-Resistant Staphylococcus aureus, and Candida albicans by using minimum inhibitory concentration (MIC) assay, while antioxidant activity was analyzed by using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging method. Results The essential oils of R. chalepensis from Jerusalem and Hebron regions have almost identical components; the major compounds identified were linalyl acetate and β-linalool; these essential oils exerted potential antioxidant and antibacterial activities. On the other hand, the major components of the plant essential oil from Jenin region were 2-undecanone and 2-nonanone, which exhibited potential antifungal activity. Conclusions The phytoconstituents and antioxidant and antimicrobial properties of the essential oil of R. chalepensis from different regions in Palestine were established in this study. The obtained results indicate possible applications for R. chalepensis in the treatment of various infectious and noninfectious diseases.

A population of 103 recombinant inbred lines (RILs, F 9 -derived lines) developed from the tworow spring barley cross L94×'Vada' was evaluated under field conditions for resistance against powdery mildew (Blumeria graminis f.sp. hordei) and scald (Rhynchosporium secalis). Apart from the major resistance gene mlo on chromosome 4 (4H), three QTLs (Rbgq1, Rbgq2 and Rbgq3) for resistance against powdery mildew were detected on chromosomes 2 (2H), 3 (3H), and 7 (5H), respectively. Rbgq1 and Rbgq2 have not been reported before, and did not map to a chromosome region where a major gene for powdery mildew had been reported. Four QTLs (Rrsq1, Rrsq2, Rrsq3 and Rrsq4) for resistance against scald were detected on chromosomes 3 (3H), 4 (4H) and 6 (6H). All four mapped to places where QTLs for scald resistance had been reported before in different populations.