Continuous Dark Conditions Research Articles

Physiological Effect of Laccase, Secreted by Rigidoporus microporus on the Host Pathogen Interactions

Laccases (EC1.10.3.2) are multi-copper containing phenol oxidases that catalyse the oxidation of phenolic compounds and aromatic amines. They are widely distributed in higher plants and in many fungi. In fungi, they are involved in delignification, sporulation, pigment production and plant pathogenesis and fruiting body formation. Rigidoporus microporus is a white rot fungus efficient lignin degradation and causative agent of the most destructive white root disease. In this study, the production of laccase was detected qualitatively. Furthermore involvement of laccase in the host-pathogen interaction was also studied. Three isolates of R. microporus were isolated from symptomatic Hevea brasiliensis (R1), Mucuna bractiata (R2), and Artocarpus nobilis (R3). The level of laccase production was measured qualitatively on solid media containing the colour indicator of guaiacol. 5 mm diameter of mycelium discs from 7 day old cultures were innoculated into 2% PDA plates supplemented with 0.2% glucose as a laccase degrading substrate with 0.02% Guaiacol (pH 5.5) and incubated at RT (28±20 C) under continuous dark conditions. After, an incubation period of 4 days, the enzyme activity was examined by the decolorisation intensity. Morphology of the three isolates was also evaluated on malt extract agar. Lignin degradation ability was studied using artificial inocula prepared by fresh root pieces of H. brasiliensis and incubated for four months; thereafter they were splited longitudinally to observe the lignin degradation ability of the isolates. All the test isolates were laccase positive and R3 (A. nobilis) isolate produced higher intensity showing comparatively larger diameter of the reddish brown halos indicting higher level of laccase production. Moreover, the isolate R3 showed the formation of rhizomorphs in vitro conditions while the other isolates did not show them. Formation of rhizormorphs is associated with the laccase synthesis which has been reported to be responsible for making polyphenolic glue that sticks the hyphae together. The degradation of roots was observed to be comparatively faster by the isolate R3 leaving white pockets on roots by degrading cell wall component due to the removal of lignin in localized areas of wood and observation can be attributed with the higher laccase enzyme. The root pieces inoculated with R1 and R2 did not show white pockets and a spongy nature until four month incubation period. It has been revealed that the isolate R3 (A. nobilis) is a good laccase producer among the other isolates under investigation. Keywords: Laccase, Rhizormorphs, Rigidoporus microporus

A brief exposure to thyroxine synchronizes the circannual testicular cycle and associated molt in the subtropical spotted munia (Lonchura punctulata)

The concept of the circannual clock has gained wide acceptance, but its genesis, physiology and mode of synchronisation in birds remain unknown. The subtropical spotted munia exhibits distinct endogenous rhythms of gonadal function, molt, fattening and food intake in ‘information-free’ conditions of continuous illumination (LL) or darkness, thus rendering it an ideal model for further investigation. The circannual reproductive rhythm in this bird is free-running, with a periodicity of approximately 10 months in LL. It appears that in order to be in harmony with the annual calendar, the endogenous rhythm must be adjusted by about 2 months every year. In our earlier experiments, daily increments in length of day just prior to the vernal equinox were found to synchronize the circannual reproductive rhythm and associated molt. The process of synchronization involves a phase delay and hence a gonado-inhibitory rather than conventional gonado-stimulatory response to increasing day length. Considering the anti-gonadal and pro-molt role of the thyroid gland (specifically thyroxine, T4) in this bird, we now examined the involvement of thyroid hormones in the process of photoperiodic synchronization. Free-running birds held in LL were administered physiological doses of T4 over 15 days during quiescence/recrudescence and regression phases, and the effects on reproductive and molt cycles were studied. The effect of LL on the thyroid hormone profile and its phase relationship with reproductive and molt cycles was also investigated. The brief exposure to thyroxine in winter synchronised the free-running reproductive and associated molt cycles in LL with the monsoon period through a phase delay. The neuroendocrine axis was shown to be sensitive to T4 during the window when photoperiodic synchronisation occurs. It appears that entrainment by daily increments of light hours may be mediated by thyroid hormones, effecting a temporary suppression of gonadotrophin secretion involving a photo-neuroendocrine locus of action.

Interactive effects of melatonin and light on growth parameters and biochemical markers in adventitious roots of Withania somnifera L.

Light plays a pertinent role in plant photo-morphogenesis and it is believed to have an impact on the melatonin-induced physiological functions. In the current study, different light regimes were employed with varying levels of melatonin, either singly or in combination with auxins for the growth and development of adventitious roots in Withania somnifera L. It was observed that 600 µM melatonin favored maximum adventitious root induction frequency (58 %) in cultures incubated under continuous dark conditions. However, adequate root growth (number and length of roots) was observed under 16 h light/8 h dark at 600 µM melatonin. Nevertheless, the interactive effect of light and melatonin was found stimulating for profound production of commercially important secondary metabolites. Correlation among growth parameters and biochemical markers was also observed in the current report. Data on total phenolic content and total flavonoid content were found at higher coincidence with each other and with DPPH antioxidant activity. In conclusion, exogenously applied melatonin mimics IAA activity in root growth and regulates well in 16-h light/8-h dark, thereby giving protection to plant system against light stress.

Rhodopsin gene expression regulated by the light dark cycle, light spectrum and light intensity in the dinoflagellate Prorocentrum.

The proton pump rhodopsin is widely found in marine bacteria and archaea, where it functions to capture light energy and convert it to ATP. While found in several lineages of dinoflagellates, this gene has not been studied in Prorocentrales species and whether it functionally tunes to light spectra and intensities as in bacteria remains unclear. Here we identified and characterized this gene in the bloom-forming Prorocentrum donghaiense. It is a 7-helix transmembrane polypeptide containing conserved domains and critical amino acid residues of PPR. This gene is phylogenetically affiliated to the xanthorhodopsin clade, but seems to have a distinct evolutionary origin. Quantitative reverse transcription PCR showed that in regular cultures, the transcript abundance of the gene exhibited a clear diel pattern, high abundance in the light period and low in the dark. The same diel pattern was observed for protein abundance with a Western blot using specific antiserum. The rhythm was dampened when the cultures were shifted to continuous dark or light condition, suggesting that this gene is not under circadian clock control. Rhodopsin transcript and protein abundances varied with light intensity, both being highest at a moderate illumination level. Furthermore, the expression of this gene responded to different light spectra, with slightly higher transcript abundance under green than blue light, and lowest abundance under red light. Transformed Escherichia coli over-expressing this rhodopsin gene also exhibited an absorption maximum in the blue–green region with slightly higher absorption in the green. These rhodopsin-promoting light conditions are similar to the relatively turbid marine habitat where the species forms blooms, suggesting that this gene may function to compensate for the light-limited photosynthesis in the dim environment.

High-efficiency direct somatic embryogenesis and plant regeneration from leaf base explants of turmeric (Curcuma longa L.)

This study describes for the first time a simple and quick direct somatic embryogenesis and plant regeneration protocol for turmeric (Curcuma longa L.) using leaf base explants. Preincubation of explants was carried out on solid Murashige and Skoog (MS) medium containing 4.49 μM 2,4-dichlorophenoxy acetic acid for 20 days under continuous dark condition. Subsequently transfer of the explants for 2 weeks to MS liquid medium containing 1.32 μM 6-benzyladenine (BA) under illuminated condition resulted in the highest percentage of somatic embryo (91.1 %) induction. Secondary somatic embryos which originated from primary somatic embryos were also observed in the same medium supplemented with 2.20 and 2.64 μM BA. Thereafter, mature somatic embryos germinated readily and the maximal plantlet development (87 %) was achieved on 1/2-strength MS medium containing gibberellic acid (GA3) under dark condition. Histological analysis revealed that the proembryogenic masses were initiated directly from the area near the vascular tissues of the leaf base explants. Presence of clear protoderm in the globular structure and procambial strands in the matured stage of somatic embryos confirmed that these structures were true somatic embryos. Somatic embryos were successfully acclimatized ex vitro at a survival rate of 72.9 % and they were normal phenotypes.

Alteration of cyanobacterial sugar and amino acid metabolism by overexpression hik8, encoding a KaiC-associated histidine kinase.

Cyanobacteria possess circadian clocks consisting of KaiABC proteins, and circadian rhythm must closely relate to the primary metabolism. A histidine kinase, SasA, interacts with KaiC to transduce circadian signals and widely regulates transcription in Synechococcus sp. PCC 7942, although the involvement of SasA in primary metabolism has not been demonstrated at metabolite levels. Here, we generated a strain overexpressing hik8 (HOX80), an orthologue of SasA in Synechocystis sp. PCC 6803. HOX80 grew slowly under light conditions and lost viability under continuous dark conditions. Transcript levels of genes related to sugar catabolism remained higher in HOX80 under dark conditions. Metabolomic analysis revealed that under light conditions, glycogen was undetectable in HOX80, and there were decreased levels of metabolites of sugar catabolism and increased levels of amino acids, compared with those in the wild-type strain. HOX80 exhibited aberrant degradation of SigE proteins after a light-to-dark transition and immunoprecipitation analysis revealed that Hik8 directly interacts with KaiC1. The results of this study demonstrate that overexpression of hik8 widely alters sugar and amino acid metabolism, revealing the involvement of Hik8 in primary metabolism under both light and dark conditions in this cyanobacterium.

Role of Neurotransmitter and Behavioral Changes in Mice due to Light- Dark Stress

Light-dark cycle has an evident role in maintaining the circadian rhythm of complex living organisms. Disturbance of light-dark cycle has an effective role in distressing the normal functions of living organisms. In this study we have analyzed the behavioral changes and role of neurotransmitter in mice due to light-dark cycle disturbances. Batches of animals were exposed to continuous light and dark conditions for 1, 2, 3, 4 and 5 days. The physiological behavior analyses such as vertical, horizontal, ambulatory and response to light-dark exposures were recorded in the disturbed and control animals. Also the role of neurotransmitter such as Dopamine, 5-HT, 5-HIAA and Homovanillic acid were estimated in the disturbed and control animal nervous tissues such as cerebrum, cerebellum and brain stem. Based on the behavioral analysis it was found that continuous light exposures have increased the horizontal and ambulatory movement of mice more significantly than the continuous dark exposed animal upon comparison with normal 12-12 dark-light exposed animals. Also the continuous light exposed animals showed an aversion to light and liking to dark upon light-dark visit but the vice versa was not found with the dark exposed animals. Dopamines and 5-HT were found down regulated in both the light and dark exposed animals significantly when compared to the normally housed animals. The identified changes in behavioral and neurotransmitter level in mice due to light-dark disturbances are impacting the fact of association of stress, sleep and circadian rhythm in mice.

Photosynthetic activation of the dark-acclimated diatom <i>Thalassiosira weissflogii</i> upon light exposure

The photoresponse of chlorophyll a (Chl a) fluorescence and xanthophyll pigments to light was studied in the diatom Thalassiosira weissflogii with respect to various durations of dark storage. The light-limited slope (α) obtained from the electron transport rate (ETR) versus the irradiance curve remained steady, whereas the light-saturated rate (ETRmax) decreased gradually during dark storage. Consequently the light-saturation index (Ek=ETRmax/α) decreased with time, suggesting that cells acclimate to dark conditions. Dark-acclimated cells were exposed to light-dark conditions with varied silicate availability. The maximum quantum yield of PSII (Fv/Fm), as well as the changes in the α and the ETRmax, increased immediately to the maximum on the first day and decreased for the second half of the light exposure period. The ratio of diatoxanthin (DT) to the xanthophyll pigment diadinoxanthin (DD) and DT (DT/[DD+DT]) represents thermal dissipation behavior through non-photochemical quenching (NPQ). This study indicates that Fv/Fm and Ek are a good index to follow photoacclimation during a transition from continuous dark conditions to the L-D cycle of saturated light. This study also indicates that dark-acclimated T. weissflogii can acclimate to the growth irradiance by the enhancement of photosynthetic activity with changes in xanthophyll pigments, in relation to the dark duration and silicate availability. Such a response to light suggests that the vegetative cells of T. weissflogii could possibly proliferate at ports in the coastal zone on a global scale after ejection into high light environments from the darkness of a ship’s ballast water tank.

Phototropic responses of potato under conditions of continuous light and subsequent darkness

The phototropic (PT) bending capacity of potato plantlets in vitro was studied under conditions of continuous light (CL) and subsequent darkness (CLD). In CL, diurnal changes characteristic for the 16/8 h LD photoperiod were absent and the response, although complex, was constant at any time of the day. Graphic representation of shoot bending indicated the presence of two separate, partly overlapping PT responses. The first was a fast, time-limited process (FPR) with a 20 min lag phase and a maximum fixed at 70 min, followed by a steady bending process (SPR) starting 50–90 min after the beginning of blue light (BL) stimulation. The FPR response rapidly deteriorated in darkness and after 60–120 min it was replaced with BL augmented circumnutations. SPR was a constant feature in darkness and while both FPR and circumnutations were absent when darkness exceeded 120 min, the SPR response remained present in darkness irrespective of its duration. The abrupt end of circumnutations marked the beginning of the synchronized SPR bending response. Darkness lasting 120 min was also a pivotal point after which the PT capacity started to recover. After 8 h of CLD, the PT capacity was fully restored. The FPR response reappeared at dawn when the light was turned on. Potato plantlets also manifested fast solar tracking movements, correcting shoot position in relation to the horizontal displacement of the BL source. Solar tracking movements contrary to circumnutations comprised shoot torsion twisting (twining). Our results demonstrate that, in potato shoots, multiple PT responses are present and operational simultaneously.

Fluctuation of Dof1/Dof2 expression ratio under the influence of varying nitrogen and light conditions: involvement in differential regulation of nitrogen metabolism in two genotypes of finger millet (Eleusine coracana L.)

In order to gain insights into the mechanism of high nitrogen use efficiency (NUE) of finger millet (FM) the role of Dof2 transcription factor (TF), which is a repressor of genes involved in C/N metabolism was investigated. The partial cDNA fragment of EcDof2 (912-bp; GenBank acc. no. KF261117) was isolated and characterized from finger millet (FM) that showed 63% and 58% homology with Dof2 of Zea mays at nucleotide and protein level, respectively. Its expression studies were carried out along with the activator EcDof1 in two genotypes (GE3885, high protein genotype (HPG); GE1437, low protein genotype (LPG)) of FM differing in grain protein contents (13.8% and 6.2%) showed that EcDof2 is expressed in both shoot and root tissues with significantly (p≤0.05) higher expression in the roots. The diurnal expression of both EcDof1 and EcDof2 in shoots was differential having different time of peak expression indicating a differential response to diurnal condition. Under continuous dark conditions, expression of EcDof1 and EcDof2 oscillated in both the genotypes whereas on illumination, the fold expression of EcDof1 was higher as compared to EcDof2. Under increasing nitrate concentration, EcDof2 expression increases in roots and shoots of LPG while it remains unchanged in HPG. However, the EcDof1 expression was found to increase in both genotypes. Further, time kinetics studies under single nitrate concentration revealed that EcDof2 was repressed in the roots of both genotypes whereas EcDof1 oscillated with time. The EcDof1/EcDof2 ratio measured showed differential response under different light and nitrogen conditions. It was higher in the roots of HPG indicating higher activation of genes involved in N uptake and assimilation resulting in high grain protein accumulation. The results indicate that both light and nitrogen concentration influence Dof1 and Dof2 expression and suggests a complex pattern of regulation of genes influenced by these plant specific TFs. In nutshell, the Dof1/Dof2 ratio can serve as an index for measuring the N responsiveness and NUE of crops and can be further validated by Dof2 knock down approach.

In vitro Morphogenesis of Arabian Date Palm (Phoenix dactylifera L.)

After inoculation of young leaves of date palm offshoot required about six months to complete the morphogenesis process. Fourteen weeks were required for embryogenic callus formation under continuous dark condition and nine weeks for shoot initiation (under 16/8 h light/dark). The highest number of explants (80%) produced callus in modified MS containing 5 mg/l 2,4-D + 2 mg/l 2ip. Sixty per cent of explants produced callus in the modified medium containing 5 mg/l 2,4-D + 5 mg/l NAA. while only 50 per cent of the explants formed callus in the same medium when supplemented with only 5 mg/l 2,4-D. The induced calli were transferred to modified MS for shoot proliferation. A combination of two cytokines showed better performance than single ones in shoot induction. The highest percentage (70) of shoot developed in modified MS containing 2 mg/l BAP + 1 mg/l Kn. Forty per cent shoot induction was found in the same medium supplemented with 2 mg/l of BAP. Thirty per cent shoot formed in MS containing 1 mg/l of Kn. The shoots were subcultured at three- four week intervals throughout culture duration. D. O. I. http://dx.doi.org/10.3329/ptcb.v23i2.17522 Plant Tissue Cult. & Biotech. 23(2): 211-219, 2013 (December)

Effect of different light regimes on esterase isozyme profiles of three species of Drosophila

Circadian rhythm has been identified in every organism studied, from unicellular marine algae to man, and in virtually all physiological and biochemical functions. The endogenous circadian system functions to organize behaviour and physiology to adapt to and anticipate environment changes in light and temperature. The present study is an attempt to understand enzyme profiles (alpha and beta esterases) of Drosophila melanogaster (Oregon-K strain), Drosophila gangotrii and Drosophila jambulina under light/dark (LD), continuous light (LL) and continuous dark (DD) conditions over 30 generations. A polyacrylamide gel electrophoresis (7.5% – native gel) was used to study the esterase isozyme banding patterns in three species of Drosophila. It has been noticed that there were three alpha esterase loci in Drosophila species which were designated as α-est 1, α-est 2 and α-est 3. Similarly there were three beta esterase loci which were designated as β-est 1, β-est 2 and β-est 3. Flies maintained in different light regimes showed differences in their allelic patterns with respect to alpha and beta esterases. It was observed that there was expression of some bands at a given light regime and the absence of the same in another regime. This shows that the different light regimes affect the expression of esterase isozymes.

Expression of the alfalfa CCCH-type zinc finger protein gene MsZFN delays flowering time in transgenic Arabidopsis thaliana

Zinc finger proteins comprise a large family and function in various developmental processes. CCCH type zinc finger protein is one kind of zinc finger protein, which function is little known. MsZFN gene encoding a CCCH type zinc finger protein was first discovered by its elevated transcript level in a salt-induced alfalfa SSH cDNA library. The previous experiment had showed that MsZFN protein was localized to the nucleus and little is known about the function of MsZFN protein and its homologous proteins in other plants including model plant, Arabidopsis thaliana. In the current study, we found that MsZFN transcript levels increased in alfalfa under continuous dark conditions and that expression was strongest in leaves and weakest in unopened flowers under light/dark conditions. Expression of MsZFN in transgenic Arabidopsis plants resulted in late flowering phenotypes under long day conditions. Yeast two-hybrid and bimolecular fluorescence complementation assays indicated that MsZFN protein can interact with itself. Transcript analyses of floral regulatory genes in MsZFN+ transgenic Arabidopsis showed enhanced expression of the flowering repressor FLOWERING LOCUS C and decreased expression of three key flowering time genes, FLOWERING LOCUS T, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS and GIGANTEA. These results suggest that MsZFN primarily controls flowering time by repressing flowering genes expression under long day conditions.

Proteomic analysis and qRT-PCR verification of Arthrospira platensis strain YZ under dark stress

Zhao X., Wang X., Zhou J., Chen B., Zeng A., Bao Q. and Wang H. 2013. Proteomic analysis and qRT-PCR verification of Arthrospira platensis strain YZ under dark stress. Phycologia 52: 538–549. DOI: 10.2216/13-167.1Arthrospira platensis is an ideal organism for a proteome study under conditions of environmental stress. Herein, we report the differential expression of proteins in A. platensis strain YZ responding to 48 h of continuous dark or light conditions by two-dimensional gel electrophoresis and peptide mass fingerprinting techniques. There were 102 proteins retrieved with significant differential expression between light and dark incubation, among which 96 protein spots were found with high homology to Arthrospira genus (67 proteins in A. platensis strain Paraca and 29 in A. maxima strain CS-328). The other six proteins belonged to other microorganisms. Using a clusters of orthologous groups database, we classified the 102 differentially expressed positive proteins into 19 types based on their function and localized them in their respective KEGG metabolic pathways. The proteins were involved in 47 metabolic pathways, such as photosynthesis, glycolysis/gluconeogenesis pathway, oxidative phosphorylation, and amino acid and fatty acid synthesis. These results implied that the proteins performed predictable roles in rendering A. platensis strain YZ resistant against dark stress. Additionally, we determined the transcriptional level of 26 genes in response to dark stress in vivo by quantitative reverse-transcription polymerase chain reaction, and we found that the expression of six differential proteins, representing 23.08% of the total target genes, was consistent between transcriptional and translational levels. The remaining 20 genes showed inconsistent protein expression compared with the transcriptional level, which accounted for 76.92% of the total target genes.

Effect of gibberellic acid- and water-based pre-soaking treatments under different temperatures and photoperiods on the seed germination of Allium stracheyi Baker: An endangered alpine species of Central Himalaya, India

Allium stracheyi Baker (Alliaceae, 2600–3000 m asl), an endangered species of Central Himalaya, India, has low seed germination in its natural habitat. This study is an attempt to improve seed germination by determining the seed viability with a low mean germination time (MGT) and germination index (GI) under optimum temperature, light, and pre-soaking treatments. The seeds were pre-soaked in hot water (80°C), cold water (10°C), and gibberellic acid (GA3 at 50 and 100 mg/l) for 24 h and subjected to light (12 h light and 12 h dark) and continuous dark (24 h) conditions with different temperature regimes (10, 15, 20, 25, and 30°C). The viability varied between 66.0% and 69.67% and declined rapidly after 12 months of storage. Our studies suggest that the 100 mg/l GA3 treatment was beneficial for seed germination and seedling growth. Pre-soaking in a 100 mg/l GA3 solution and incubation at 20°C under light conditions enhanced the germination significantly (p < 0.05) and resulted in the highest (97.3%) germination with the lowest MGT = 5.7 days, with GI = 8.11. The recommendations of this study support the conservation of alpine A. stracheyi via simple and cost-effective techniques for optimal seed germination.

Hd16, a gene for casein kinase I, is involved in the control of rice flowering time by modulating the day‐length response

The alteration of photoperiod sensitivity has let breeders diversify flowering time in Oryza sativa (rice) and develop cultivars adjusted to a range of growing season periods. Map-based cloning revealed that the rice flowering-time quantitative trait locus (QTL) Heading date 16 (Hd16) encodes a casein kinase-I protein. One non-synonymous substitution in Hd16 resulted in decreased photoperiod sensitivity in rice, and this substitution occurred naturally in an old rice cultivar. By using near-isogenic lines with functional or deficient alleles of several rice flowering-time genes, we observed significant digenetic interactions between Hd16 and four other flowering-time genes (Ghd7, Hd1, DTH8 and Hd2). In a near-isogenic line with the weak-photoperiod-sensitivity allele of Hd16, transcription levels of Ehd1, Hd3a, and RFT1 increased under long-day conditions, and transcription levels of Hd3a and RFT1 decreased under short-day conditions. Expression analysis under continuous light and dark conditions showed that Hd16 was not likely to be associated with circadian clock regulation. Biochemical characterization indicated that the functional Hd16 recombinant protein specifically phosphorylated Ghd7. These results demonstrate that Hd16 acts as an inhibitor in the rice flowering pathway by enhancing the photoperiod response as a result of the phosphorylation of Ghd7.

Acute Toxicity of TiO2 Nanoparticles to Ceriodaphnia dubia under Visible Light and Dark Conditions in a Freshwater System

The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO2 NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO2 NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO2 NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining.

Ethylene- and dark-induced flower abscission in potted Plectranthus: Sensitivity, prevention by 1-MCP, and expression of ethylene biosynthetic genes

Prevention of ethylene- and shipping-induced flower abscission is necessary to maintain the quality of both cut flowers and potted plants during handling, transport and retail display. The aims of the present work were to determine the sensitivity of Plectranthus cultivars to applied ethylene, to alleviate ethylene- and shipping-induced flower abscission in intact potted plants using 1-methylcyclopropene (1-MCP), and to investigate the possible causes of dark-induced flower abscission. All cultivars were sensitive to ethylene in a concentration-dependent manner, and complete abscission occurred within 24h with 1 and 2μll−1 ethylene. Unopened buds were more sensitive to applied ethylene, and exhibited greater abscission than open flowers. Ethylene synthesis remained below detection limits at all time points under control and continuous dark conditions. Dark treatment significantly increased flower abscission in Plectranthus cultivars, and like ethylene-induced flower abscission, this could be prevented by continuous 1-MCP treatment. Gene expression of ethylene biosynthetic enzymes ACS and ACO was examined as possible causes for the accelerated flower abscission observed in plants kept in continuous darkness. Expression patterns of ACS and ACO varied between different cultivars of Plectranthus. In some cases, increased expression of ACS and ACO led to increased flower abscission. Gene expression was higher in open flowers when compared to unopened flowers suggesting a cause for the observed preferential shedding of open flowers in some cultivars. Although the cause of dark-induced abscission in Plectranthus remains elusive, it can be effectively controlled by treatment with 1-MCP.

The effect of irradiance and temperature on the role of photolysis in the removal of organic micropollutants under Antarctic conditions

Environmental context Antarctica has several scientific research stations located along its coast, where they discharge often untreated sewage containing organic micropollutants. Although degradation of these pollutants by microorganisms is limited by the cold conditions, other pathways such as photodegradation may be significant. Our results indicate that, during the summer, photolysis is a potentially significant degradation pathway for organic micropollutants in Antarctic surface waters, although the rate of loss would depend on ice cover and water depth. Abstract Knowledge of the environmental fate of organic micropollutants in Antarctica is limited, especially with respect to photolysis. The Antarctic is characterised by extreme light conditions of either continuous sunshine or darkness depending on the season. The photolytic degradation of benzophenone-3 (BP-3), bisphenol A (BPA), 17α-ethinylestradiol (EE2), methyl paraben (mParaben), 4-t-octylphenol (4-t-OP) and triclosan in MilliQ and seawater was investigated over a range of irradiance levels and temperatures. Photodegradation was compound specific. Up to 20% of BPA, BP-3 and EE2 was degraded over a 7-h irradiance period. Triclosan and 4-t-OP degraded to below the limit of detection in all experiments whereas mParaben was not degraded. The degradation of triclosan increased with irradiance in both MilliQ (P=2.2×10–16) and seawater (P=2.2×10–16). The degradation of 4-t-OP increased with irradiance in MilliQ (P=8.5×10–9) and seawater (P=1.1×10–5), and with temperature in MilliQ (P=8.5×10–9) and seawater (P=1.0×10–5). Similar relationships could not be established for BPA, BP-3, EE2 and mParaben due to the limited extent of degradation observed. The photolysis of triclosan was enhanced 4-fold in seawater compared to MilliQ water. Results from this study indicate that micropollutants may persist for extended periods of time in Antarctic coastal waters, particularly with ice cover, above and beyond that exhibited in temperate seawater.

Impact of Photoperiod on the Circadian Cellulose and Cellulase Rhythms in the Digestive System of Silkworm, Bombyx Mori

Circadian cellulose and cellulase rhythms were studied in the digestive system of Bombyx mori under 12 hr light-dark cycle (LD), continuous light (LL) and continuous dark (DD) conditions. Since, the symbiotic microbes are associated with cellulose digestion in the silkworm; both the rhythms are presumed to have microbial origin. The rhythms were analyzed in terms of phase response curves and interpreted as cellulose synthetic cycles (CS cycles) and cellulase enzyme synthetic cycles (CES cycles) in gut wall and cellulose uptake cycles (CU cycles) and cellulase enzyme release cycles (CER cycles) in gut lumen. The cellulose rhythm in the gut wall maintained 7 CS cycles each with a duration of 3.4 hr and the 24 hr free running time remained unchanged under altered photoperiodic conditions. In gut lumen, the rhythm showed 7 CU cycles, each with a duration of 3.4 hr under LD and 6 CU cycles of 4.0 hr each under LL and DD, with the result, the 24 hr free running period of the rhythm was clock shifted to 28 hr both under LL and DD. The cellulase rhythm in the gut wall maintained 7 CES cycles with a duration of 3.4 hr each under LD and DD and 9 cycles each with a duration of 2.7 hr under LL. The 24 hr free running time of the cellulase rhythm of LD and DD, was thus advanced to 19 hr under LL. The cellulase in gut lumen maintained 6 CER cycles with a duration of 4.0 hr each, under LD, LL and DD and hence the 24 hr free running time of the rhythm was not affected. Further analysis of data showed that cellulose synthesis was stimulated by light cues, while its uptake from gut lumen through enhanced microbial cellulase activity was favoured by both diet and light cues.