light regimes
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AbstractIt remains unclear as to how mixoplankton (coupled phototrophy and phagotrophy in one cell) affects the estimation of grazing rates obtained from the widely used dilution grazing technique. To address this issue, we prepared laboratory-controlled dilution experiments with known mixtures of phyto-, protozoo-, and mixoplankton, operated under different light regimes and species combinations. Our results evidenced that chlorophyll is an inadequate proxy for phytoplankton when mixoplankton are present. Conversely, species-specific cellular counts could assist (although not fully solve) in the integration of mixoplanktonic activity in a dilution experiment. Moreover, cell counts can expose prey selectivity patterns and intraguild interactions among grazers. Our results also demonstrated that whole community approaches mimic reality better than single-species laboratory experiments. We also confirmed that light is required for protozoo- and mixoplankton to correctly express their feeding activity, and that overall diurnal grazing is higher than nocturnal. Thus, we recommend that a detailed examination of initial and final plankton communities should become routine in dilution experiments, and that incubations should preferably be started at the beginning of both day and night periods. Finally, we hypothesize that in silico approaches may help disentangle the contribution of mixoplankton to the community grazing of a given system.

The features of the diurnal dynamics of the area of rat hepatocyte nuclei and their ploidy were studied under conditions of a standart (fixed) light regime and constant illumination, as well as under chronic exposure to alcohol in the mentioned light regimes. It has been shown that exposure to alcohol and exposure to constant illumination separately lead to a change in the amplitude-phase characteristics of the circadian rhythm of the nucleus area, while the combined effect of these factors leads to a complete destruction of the rhythm, which indicates a violation of adaptation processes. An increase in the average ploidy of hepatocyte nuclei in chronic alcohol intoxication is also shown, while in animals kept under constant illumination without drinking alcohol, the values of this parameter decrease, which indicates a successful course of the adaptation process. The conducted research indicates that the results of karyometric and ploidometric analysis characterize the degree of influence of alcohol intoxication and changes in the light regime on the liver of rats, reflecting the rate of efficiency of adaptation to these factors.

Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes.

Carob (Ceratonia siliqua L.) is an important Mediterranean plant species with worldwide commercial and medicinal uses. The establishment of a callus culture protocol as an alternative system to produce polyphenols of chemical and pharmaceutical interest was made in the present study for the first time in carob. Explant type and the light regime are two important factors that influence morphogenic responses and biochemical production. Maximal callus induction (100 %) and biomass accumulation were obtained in cotyledon explants under both tested light regimes (16-hour photoperiod and darkness). However, leaf callus produced a higher amount of polyphenols (TPC) and flavonoids (TFC) but a lower amount of total condensed tannins (TCT) as compared to cotyledon callus. Light treatment has significantly increased TCT content but decreased the antioxidant activity in carob callus cultures. Strong and positive correlations were obtained between TPC and TFC and the antioxidant activities with correlation coefficients ranging between 0.68 and 0.98. The obtained results indicate that calli of C. siliqua have the potential for enhanced production of phenolic compounds with antioxidant activity that is favored by culture under dark condition.

Restocking programmes of different fish species have been implemented worldwide. However, the survival of hatchery-reared fish after release to riverine ecosystems is at a very low level. One of the reasons for the high mortality rate of post-released fish is their modified swimming behaviour due to the hatchery rearing practice. To investigate one of the possible causes for modified swimming behaviour, Acipenser baerii larvae were exposed to surface- and bottom-feeding applications with day and night light regimes in a factorial design. We also analysed the effect of 5 and 10 days of starvation after different feeding applications on sturgeon swimming behaviour. The surface-feeding application was previously expected to promote the frequent Siberian sturgeon swim up to the mid- and top-water layers in our rearing facilities. However, our results indicated that the modified behaviour of the Siberian sturgeon in our study was caused by fish starvation and a possible predator-free environment rather than by the method of feed application or the day/night light regimes. These results may be used to improve the implementation of restocking programmes either through modified hatchery rearing practice or the training of foraging skills with predator stimuli.

Although the relationship between polyamines and photosynthesis has been investigated at several levels, the main aim of this experiment was to test light-intensity-dependent influence of polyamine metabolism with or without exogenous polyamines. First, the effect of the duration of the daily illumination, then the effects of different light intensities (50, 250, and 500 μmol m–2 s–1) on the polyamine metabolism at metabolite and gene expression levels were investigated. In the second experiment, polyamine treatments, namely putrescine, spermidine and spermine, were also applied. The different light quantities induced different changes in the polyamine metabolism. In the leaves, light distinctly induced the putrescine level and reduced the 1,3-diaminopropane content. Leaves and roots responded differently to the polyamine treatments. Polyamines improved photosynthesis under lower light conditions. Exogenous polyamine treatments influenced the polyamine metabolism differently under individual light regimes. The fine-tuning of the synthesis, back-conversion and terminal catabolism could be responsible for the observed different polyamine metabolism-modulating strategies, leading to successful adaptation to different light conditions.

Light plays a fundamental role in the ecology of organisms in nearly all habitats on Earth and is central for processes such as vision and the entrainment of the circadian clock. The poles represent extreme light regimes with an annual light cycle including periods of Midnight Sun and Polar Night. The Arctic Ocean extends to the North Pole, and marine light extremes reach their maximum extent in this habitat. During the Polar Night, traditional definitions of day and night and seasonal photoperiod become irrelevant since there are only “twilight” periods defined by the sun’s elevation below the horizon at midday; we term this “midday twilight.” Here, we characterize light across a latitudinal gradient (76.5° N to 81° N) during Polar Night in January. Our light measurements demonstrate that the classical solar diel light cycle dominant at lower latitudes is modulated during Arctic Polar Night by lunar and auroral components. We therefore question whether this particular ambient light environment is relevant to behavioral and visual processes. We reveal from acoustic field observations that the zooplankton community is undergoing diel vertical migration (DVM) behavior. Furthermore, using electroretinogram (ERG) recording under constant darkness, we show that the main migratory species, Arctic krill (Thysanoessa inermis) show endogenous increases in visual sensitivity during the subjective night. This change in sensitivity is comparable to that under exogenous dim light acclimations, although differences in speed of vision suggest separate mechanisms. We conclude that the extremely weak midday twilight experienced by krill at high latitudes during the darkest parts of the year has physiological and ecological relevance.

Shoot branching is a complex mechanism in which secondary shoots grow from buds that are initiated from meristems established in leaf axils. The model plant Arabidopsis thaliana has a rosette leaf growth pattern in the vegetative stage. After flowering initiation, the main stem starts to elongate with the top leaf primordia developing into cauline leaves. Meristems in arabidopsis are initiated in the axils of rosette or cauline leaves, giving rise to rosette or cauline buds, respectively. Plasticity in the process of shoot branching is regulated by resource and nutrient availability as well as by plant hormones. However, few studies have attempted to test whether cauline and rosette branching are subject to the same plasticity. Here, we addressed this question by phenotyping cauline and rosette branching in three arabidopsis ecotypes and several arabidopsis mutants with varied shoot architectures. Our results show that there is no negative correlation between cauline and rosette branch numbers in arabidopsis, demonstrating that there is no trade-off between cauline and rosette bud outgrowth. Through investigation of the altered branching pattern of flowering pathway mutants and arabidopsis ecotypes grown in various photoperiods and light regimes, we further elucidated that the number of cauline branches is closely related to flowering time. The number or rosette branches has an enormous plasticity compared with cauline branches and is influenced by genetic background, flowering time, light intensity and temperature. Our data reveal different plasticity in the regulation of branching at rosette and cauline nodes and promote a framework for future branching analyses.