Chlorophyll Degradation Products Research Articles

Environmental impact of potentially toxic elements accumulated in surface sediments of the Erikli Lagoon, Black Sea coast (Türkiye)

This study aims to (a) determine the concentration and distribution of elements in the surface sediments of the Erikli Lagoon, which are under natural and anthropogenic pressure, (b) determine possible effects on the environment using ecological indices, and (c) reveal possible sources. Multiple elements, total organic carbon and chlorophyll degradation products were analyzed in sediment samples. Enrichment factor (EF), contamination factor (CF), and geoaccumulation index (Igeo) were calculated to determine the sources of the elements. Modified hazard quotient (mHQ), ecological contamination index (ECI), contamination severity index (CSI) and potential ecological risk index (PERI) were calculated to determine ecological risks. It was found that Mn, Hg, As, Fe and Cd entering the lake are of anthropogenic origin. These elements pose a low to moderate ecological threat to the lake. Agricultural and domestic discharges and atmospheric deposition are the main sources of these elements. A moderate ecological risk with an average value of 194.89 was determined in the lagoon based on PERI and contamination levels of metals. The elements that pose this risk are Hg and Cd, due to their high toxicity. According to ECI and CSI, the ecological risk is low, with average values of 0.99 and 0.30, respectively.

Chlorophyll Degradation and its Physiological Function.

Research on chlorophyll degradation has progressed significantly in recent decades. In the 1990s, the structure of linear tetrapyrrole, which is unambiguously a chlorophyll degradation product, was determined. From the 2000s until the 2010s, the major enzymes involved in chlorophyll degradation were identified, and the pheophorbide a oxygenase/phyllobilin pathway was established. This degradation pathway encompasses several steps: (1) initial conversion of chlorophyll b to 7-hydroxymethyl chlorophyll a; (2) conversion of 7-hydroxymethyl chlorophyll a to chlorophyll a; (3) dechelation of chlorophyll a to pheophytin a; (4) dephytylation of pheophytin a to pheophorbide a; (5) opening of the macrocycle to yield a red chlorophyll catabolite; and (6) conversion of red chlorophyll catabolite to phyllobilins. This pathway converts potentially harmful chlorophyll into safe molecules of phyllobilins, which are stored in the central vacuole of terrestrial plants. The expression of chlorophyll-degrading enzymes is mediated by various transcription factors and influenced by light conditions, stress, and plant hormones. Chlorophyll degradation is differently regulated in different organs and developmental stages of plants. The initiation of chlorophyll degradation induces the further expression of chlorophyll-degrading enzymes, resulting in the acceleration of chlorophyll degradation. Chlorophyll degradation was initially considered the last reaction in senescence; however, chlorophyll degradation plays crucial roles in enhancing senescence, degrading chlorophyll-protein complexes, forming photosystem II, and maintaining seed quality. Therefore, controlling chlorophyll degradation has important agricultural applications.

Unprecedented sea-ice minima enhances algal production deposited at the Arctic seafloor

Sea-ice in the Arctic is declining, with 2018 a particularly low year for ice extent, driven by anomalously warm atmospheric circulation in winter 2017/18. This is consistent with a multi-decadal trend to an earlier ice-free Barents Sea as climate change rapidly warms the Arctic. Here we investigate a N–S transect in the Barents Sea, crossing the Polar Front from Atlantic waters in the south to Arctic waters in the north, focusing on the organic geochemical signature (pigments and lipids) in surface sediments sampled in summer, between the years of 2017–19. Early ice-out in summer 2018 was confirmed by satellite imagery, tracking the evolution of Arctic sea-ice extent between years. Consistent with less extensive sea-ice cover in 2018 we found increases in multiple chlorophyll and carotenoid pigments as well as fatty acids (reflecting recent phytoplankton delivery) in the northern part of our transect at the seafloor. We attribute this to nutrient and organic matter release from earlier 2018 ice-out leading to stratification, post-melt phytoplankton blooms and the deposition of organic matter to the seafloor, evidenced by pigments and lipids. Organic matter delivered to the seafloor in 2018 was reactive and highly labile, confirming its deposition in the most recent season, pointing to rapid deposition. Correlations were found during ice-free periods between satellite-derived chlorophyll a and multiple indicators of water column productivity deposited at the seafloor. We also found convincing evidence of multi-year biogeochemical change across the Polar Front, where sedimentary change is marked by chlorophyll degradation products providing evidence of grazing, indicative of a tightly coupled ecosystem close to the marginal ice zone. Overall, our results show the tight coupling of Arctic productivity with the delivery and quality of organic matter to the seafloor and how this varies across the Barents Sea. More frequent early summer sea-ice loss driven by climate warming in the Barents Sea will have consequences for the delivery of organic matter to the seafloor with impacts for benthic organisms, microbiology and the sequestration of carbon.

A critical assessment of the Candida strains isolated from cigar tobacco leaves.

Introduction: Candida genus plays a crucial role in cigar fermentation, and strains from different sources might have differences in metabolic characteristics. Therefore, this study conducted directional isolation of Candida strains from cigar tobacco leaves and compared their fermentabilities to screen suitable strains for cigar fermentation, thereby improving the cigar quality. Methods: First, the Candida strains from cigars tobacco leaves in different production areas were directionally isolated by pure culture. Then, the isolated strains were screened based on chemical indexes and flavor component contents. Finally, the fermentabilities of preferred strains were verified by sensory evaluation. Results: Five strains of C. parapsilosis and four strains of C. metapsilosis were obtained through directional isolation. By comparing the physicochemical indexes of nine strains of Candida, it was found that C. parapsilosis P1 and C. metapsilosis M4 not only reduced the alkaloids content (by 25.3% and 32.6%, respectively) but also increased the flavor components content (by 25.2% and 18.9%, respectively). Among them, P1 could raise the content of chlorophyll degradation products, carotenoid degradation products, and Maillard reaction products, and enhance the beany and nutty flavor of cigars. M4 could raise the content of chlorophyll degradation products, cembranoids degradation products, and Maillard reaction products, and improve the baking, nutty, cocoa, and honey flavor of the cigar. Discussion: In this study, the Candida strains were directionally isolated from cigars tobacco leaves in different production areas, and two functional strains suitable for cigar fermentation were screened based on physicochemical indexes and sensory evaluation, which would contribute to the directed regulation of cigar quality and flavor diversification.

Analysis of Toxic Metal-Induced Ecological Risk in Kepez Stream, Çanakkale, Türkiye

Ecological risk in the mouth of Kepez Stream has recently increased notably due to waste from the Kepez settlement, agricultural activity in the Kepez delta, maritime traffic in the Çanakkale Strait, and summer houses in the coastal area. This study analyzed the ecological risk of 10 sediment samples along the bed in the mouth of Kepez Stream to shed light on anthropogenically induced pollution. The pollution proxies such as chlorophyll degradation products, heavy metal concentrations and organic carbon of the sediment samples were determined. Enrichment Factor (EF), Contamination Factor (CF), Geoaccumulation Index (Igeo) and Potential Ecological Risk Index (PER) were calculated from the results obtained. Spearman's correlation analysis and factor analysis were also performed. The obtained data show that there is moderate enrichment of Zn, As and Co, a significant level of Pb, and very high level of Cr in the sediments of Kepez Stream. Ni enrichment was determined to be excessive and poses a high potential ecological risk. Cleaning and rehabilitation need to be carried out urgently in the mouth of Kepez Stream. It should be determined whether metals are being transmitted to aquatic organisms, and measures should be taken to reduce the sources of pollution.

Element-based ecological and human health risk assessment in a lagoon system in a densely populated basin

This study analysed the ecological deterioration and health risk in sediment samples taken from Dalyan and Poyraz Lagoons in the Karacabey floodplain of Turkey, which is under pressure from agriculture, industry and settlement activities. Multi-element analyses were performed with ICP-MS on the surface and core sediment samples from the lagoons. Total organic carbon, chlorophyll degradation products and carbonate analyses were performed to determine the transport and illuviation dynamics of the elements. While Pb and Zn showed moderate enrichment at some sampling points, no enrichment of the other elements was detected. According to ecological risk analysis data, Cd and Hg posed a moderate ecological risk at some sampling points. The modified hazard quotient data indicated very high contamination of Ni, a high level of As contamination and significant Cr contamination. A carcinogenic health risk was detected from Ni, Cr and As due to the lithological characteristics of the basin. It was concluded that the lithological characteristics, the agricultural and mining activities carried out in the Susurluk Basin – which is drained by Koca Stream – and domestic and industrial waste contributed to the higher element concentrations in the Karacabey floodplain.

Temperature-induced zeaxanthin overproduction in Synechococcus elongatus PCC 7942.

The exogenous crtZ gene from Brevundimonas sp. SD212, coding for a 3,3' β-car hydroxylase, was expressed in Synechococcus elongatus PCC 7942 under the control of a temperature-inducible promoter in an attempt to engineer the carotenoid metabolic pathway, to increase the content of zeaxanthin and its further hydroxylated derivatives caloxanthin and nostoxanthin. These molecules are of particular interest due to their renowned antioxidant properties. Cultivation of the engineered strain S7942Z-Ti at 35°C, a temperature which is well tolerated by the wild-type strain and at which the inducible expression system is activated, led to a significant redistribution of the relative carotenoid content. β-Carotene decreased to about 10% of the pool that is an excess of a threefold decrease with respect to the control, and concomitantly, zeaxanthin became the dominant carotenoid accounting for about half of the pool. As a consequence, zeaxanthin and its derivatives caloxanthin and nostoxanthin collectively accounted for about 90% of the accumulated carotenoids. Yet, upon induction of CrtZ expression at 35°C the S7942Z-Ti strain displayed a substantial growth impairment accompanied, initially, by a relative loss of carotenoids and successively by the appearance of chlorophyll degradation products which can be interpreted as markers of cellular stress. These observations suggest a limit to the exploitation of Synechococcus elongatus PCC 7942 for biotechnological purposes aimed at increasing the production of hydroxylated carotenoids.

Photodynamic antitumor activity of tetrahydroxyl-methyl pyropheophorbide-a with improved water-solubility and depth of treatment

Methyl pyropheophorbide-a (MPPa) is a chlorophyll degradation product that possesses excellent photophysical and photochemical properties, yet poor water solubility limits its clinical application. In this paper, a novel MPPa derivative, 31,32,7,8-tetrahydroxy-4 H-MPPa (HMPPa) was synthesized by oxidative hydrolysis of MPPa with potassium osmate. The four hydrophilic hydroxyl groups endow HMPPa with better water solubility (lipid water partition coefficient logP = −0.16), which solve the problem of MPPa aggregation in water. HMPPa has a long-wavelength near-infrared absorption at 740 nm that can achieve a deeper penetration depth in biological tissues, which allows HMPPa to be applied in deep tumor therapy. Moreover, HMPPa possesses a higher singlet oxygen quantum yield (62.65 %) than that of MPPa (56 %). MTT assay verified that HMPPa had a strong ability to inhibit the growth of HepG-2 cells and 4T1 cells, and the PDT effect was superior to that of MPPa. Cell morphology experiments and flow cytometry analysis showed that HMPPa could induce apoptosis via a mitochondrial pathway. In vivo study of HMPPa showed a significant PDT antitumor effect on 4T1 tumor-bearing mice (Balb/C). The tumor cells followed by treatment of HMPPa could be clearly observed under fluorescence microscopy, implying a good fluorescence imaging function of HMPPa.

Environmental impact of fish farming: assessment of metal contamination and sediment geochemistry at three aquaculture areas from the eastern Aegean coast.

Metal contamination and geochemistry of surface sediments were assessed at three aquaculture sites from the eastern Aegean coast. The chlorophyll degradation products and organic carbon levels were used as indicators of eutrophication status. In Akköy, higher Hg, Pb, and Cd levels were observed around the cages, while maximum concentrations of other elements were determined at stations situated near the Büyük Menderes River estuary. Metal concentrations were less than the central Aegean coast background levels other than Zn, Ni, and Cr in Akköy. Several approximations have been utilized to evaluate potential toxicity of sediments and sediment quality guidelines (SQG) were used to estimate the risks for aquatic life. Ni was the only metal with concentrations exceeding all SQG values, which indicates the highest adverse biological effect in Ildır, Akköy, and occasionally toxic in Güllük. Based on QPEL and QTEL, Ni and Cr were the predominant metal contaminants in all areas. Similarly, Cr and Ni account for the most of the all sediment toxicity in the aquaculture areas according to toxic risk index. It is concluded that sediments around the fish farms are affected by growing input of elements because of aquaculture activity. The levels of chlorophyll degradation products showed oligotrophic and mesotrophic conditions in the three studied aquaculture areas.

Biofilm pigments in temporary streams indicate duration and severity of drying

AbstractIncreased duration and frequency of droughts under global change may affect both temporary and formerly permanent watercourses. Streambed desiccation, cooccurring solar radiation, and high temperature all may affect the composition and metabolism of photoautotrophic organisms in benthic biofilms. To test these effects, we characterized the composition of pigments when biofilms were exposed to dry conditions, and compared this to pigments measured after flow resumed, as well as to others measured from permanent streams in the same region. This comparison revealed important differences in pigmentary composition based on flow conditions. Active chlorophylls decreased exponentially with the duration and severity of the nonflow period, while chlorophyll degradation products and protective carotenoids increased. Streams experiencing longer and more severe nonflow periods showed the highest dissimilarities in their biofilm pigmentary composition, and this pattern was maintained after flow resumed. Our results pointed to duration of nonflowing periods as the major driver of pigmentary composition, regardless of whether these were interrupted or not by short intervals of water flows. Multivariate changes in pigmentary composition between sampling periods highlighted the influence of the long‐term hydrological history on the relative abundance of different taxonomic groups and their associated pigments. Overall, pigmentary fingerprints are informative of the biofilm capacity to resist water flow interruption and of their ability to recover after water flow returns.

Visible Light-Induced Antibacterial Activity of Pigments Extracted from Dregs of Green and Black Teas.

Chlorophyll and its derivatives are potential natural sensitizers frequently applied in antimicrobial photodynamic therapy. Chlorophyll derivatives are formed naturally during tea processing, but they do not contribute to the color of tea infusions and thus are presumably left in the tea dregs. The present study aimed to investigate (i) the chlorophyll remnants in the pigments recovered from dregs of green and black teas and (ii) the antibacterial activity of pigments extracted from the tea dregs upon illumination using a light-emitting diode (LED) as the light source. Pigment analysis using high-performance liquid chromatography (HPLC) revealed the presence of main degradation products of chlorophylls, such as pheophytin and its epimers, pyropheophytin, and pheophorbides. In vitro assays demonstrated significant reductions in the number of viable bacteria in the presence of the pigments after 30 min of incubation with LED light irradiation. The descending order of bacterial susceptibility was Listeria monocytogenes > Staphylococcus aureus > Escherichia coli > Salmonella typhi. At an equivalent irradiation intensity, the blue and red LEDs could stimulate a comparable inactivation effect through photodynamic reactions. These findings demonstrated the valorization potential of tea dregs as a source of chlorophyll derivatives with visible light-induced antibacterial activity.

Distribution, sources and ecological risk assessment of metals in Kura river sediments along a human disturbance gradient

Monitoring the pollution status of freshwater resources is an important step in sustainable planning. This study aimed to determine the distribution and sources of metals in the sediments of the transboundary eastern Anatolian/Caucasus region Kura river as well as its ecological risk level. Surface sediment samples were collected from eight sites along the human disturbance gradient. Multi-element analyses of the collected samples were performed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Chlorophyll degradation product (CDP) analysis was performed spectrophotometrically. OC analysis was carried out using the titration method. The data obtained were evaluated using the indices of enrichment factor, geo-accumulation, modified hazard quotient and ecological contamination index and potential ecological risk. The average content of metals in the sediment at the eight sites was of the following descending order from highest to lowest: Al > Mn > Zn > V> Ni > Cr > Cu > Co > Pb > As > Cd > Tl > Hg. According to the distribution of raw metal values, urbanization is not the only factor controlling metal distribution. Adsorption processes and organic material content also emerge as an important factor. Enrichment factor values were of the following order: T1 > Pb > Mn > Hg > Cr > Co > Cd > Ni > As > Zn > Al > Cu > V. Results revealed that the sources of Cu, V and Al were lithogenic, in contrast to Tl, Pb, Mn, Hg, Cr, Co, Cd, Ni, and As, thus pointing to human-induced accumulation. According to the potential ecological risk index, these elements have the potential to create medium-to-high level ecological risks and were substantially of atmospheric origin. The ecological contamination index is also consistent with these findings in terms of risk level. A municipal waste stream, fossil fuel burning and a cement plant operating in close proximity also appeared to be the possible sources.

An evergreen mind and a heart for the colors of fall

With finest biochemical and molecular approaches, convincing explorative strategies and long-term vision, Stefan Hörtensteiner succeeded in elucidating the biochemical pathway responsible for chlorophyll degradation. After having contributed to the identification of key chlorophyll degradation products in the course of the last twenty-five years, he gradually identified and characterized most of the crucial players in the PAO/phyllobilin degradation pathway of chlorophyll. One of the brightest plant biochemists of his generation, his work opened doors to a better understanding of plant senescence, tetrapyrrole homeostasis and their complex regulation. He sadly passed away on 5 December 2020, aged 57.

Taxon- and senescence-specific fluorescence of colored leaves from the Pliocene Willershausen Lagerst\xe4tte, Germany

UV-light-induced fluorescence is widely used in the study of coal macerals and palynological samples, but to date has not been described in great detail for plant macrofossils. Here, we report the characteristics of bright UV-light-induced fluorescence of various fossil angiosperm leaf taxa from the Upper Pliocene of Willershausen, Lower Saxony, Germany. The fluorescence is exceptional, since different fluorescence colors ranging from green to yellow to red can be observed and fluorescence properties are found to be related to genera. Using confocal laser scanning microscopy, fluorescence was studied in detail and emission spectra were obtained that allowed to differentiate broad groups of fluorophores. Fluorescence emissions attributed to chlorophyll degradation products demonstrate that fluorescence can be used as an indicator for exceptional chemical preservation of leaf fossils. Comparison with present-day senescing plants suggests that the fluorescence differences in the fossil leaves are mainly caused by taxon-specific degeneration of organic compounds during senescence. The occurrence of various leaf taxa with different fluorescence properties, preserved under identical conditions of fossilization, indicate that diagenesis was not crucial for the differences in leaf fluorescence.

Geographical information systems based ecological risk analysis of metal accumulation in sediments of İkizcetepeler Dam Lake (Turkey)

This study analyzed the spatial distribution, potential ecological risks and possible sources of metal concentrations, organic carbon, chlorophyll degradation products and CaCO3 content from surface sediment samples in İkizcetepeler Dam Lake using ecological-toxicological indices, multivariate statistical analysis, and geographical information systems (GIS) software. One core sample and 32 surface sediments were taken from the Dam Lake, while seven lithologic samples were taken from various points in the basin. To identify anthropogenic influences in the Dam Lake from the before dam was constructed period to the present day, the enrichment factor (EF), contamination factor (CF), geoaccumulation index (Igeo), toxic risk index (TRI) and pollution load index (PLI) indices were calculated based on lithologic background values. Modified ecological risk (mER) and modified potential ecological risk (mPER) were calculated separately according to core sample and lithologic background values. Therefore, ecological risk during Anthropocene was determined using core sample values. Results pointed to significant enrichment of Ni (6.93), moderate enrichment of As (3.88), Cr (2.86), Mn (2.54), Hg (2.34), and Cd (2.04) and low level enrichment of Pb (1.20), Cu (1.15), Zn (1.08), and Fe (0.80). Ecological risk was listed as Hg (94) > Cd (61) > As (38) > Ni (35) > Cu (5.98) > Cr (5.72) > Pb (5.68) > Zn (1.07) according to lithologic background values and as Hg (59) > Cd (29) > As (9) > Ni (8) > Cu (7) > Pb (5) > Cr (2.97) > Zn (1.42) according to core background values. A significant level of ecological risk was determined for Hg (94), medium level ecological risk for Cd (61), and close to moderate level ecological risk for As (38) and Ni (35). The risk was low for all the other metals. According to the core sample background values, ecological risk was at the lowest limit of the most significant level for Hg (81), moderate for Cd (50) and low for other metals. Overall, this indicates a low (123) and moderate (201) potential ecological risk in İkizcetepeler Dam Lake based on core and lithologic background values, respectively.

Pyrrolic and Dipyrrolic Chlorophyll Degradation Products in Plants and Herbivores.

The degradation of chlorophyll, the omnipresent green pigment, has been investigated intensively over the last 30 years resulting in many elucidated tetrapyrrolic degradation products. With a comparison to the degradation of the structurally similar heme, we hereby propose a novel additional chlorophyll degradation mechanism to mono‐ and dipyrrolic products. This is the first proof of the occurrence of a family of mono‐ and dipyrrols in leaves that are previously only known as heme degradation products. This product family is also found in spit and feces of herbivores with specific metabolomic patterns reflecting the origin of the samples. Based on chromatographic and mass spectrometric evidence as well as on mechanistic considerations we also suggest several tentative new degradation products. One of them, dihydro BOX A, was fully confirmed as a novel natural product by synthesis and comparison of its spectroscopic data.

Response of photosynthesis to different concentrations of heavy metals in Davidia involucrata.

Lead (Pb) and cadmium (Cd) are highly toxic and are widespread in agricultural soils, representing risks to plant and human health. In this study, Davidia involucrata was cultivated in soil with different concentrations of Pb and Cd and sampled after 90 days. We used ANOVA to analyse the photosynthesis of D. involucrata and the ability of Pb and Cd to enrich and migrate in roots, stems and leaves. Various results are described here. 1) Under individual and combined Pb and Cd stress, the accumulation factors in the roots were greater than 1, which was significantly greater than those in the stems and leaves (P < 0.05), and the translocation factors both were less than 1. The Pb and Cd enrichment ability of D. involucrata roots was significantly higher than that of stems and leaves, and the migration ability of the two heavy metals in D. involucrata was weak. 2) The Mg-dechelatase activities of chlorophyll degradation products increased under stress due to high concentrations of Pb and Cd. However, chlorophyllase activity was higher at relatively low concentrations of the two heavy metals (P < 0.05). δ-Aminolevulinic acid and porphobilinogen of chlorophyll synthesis products are easily converted to uroporphyrinogen III under low concentrations of Cd, which promotes the synthesis of chlorophyll. 3) The effect of Cd stress alone on the chlorophyll concentration was not significant. Under combined stress, concentrations of Pb and Cd in the range of 400~800 mg·kg-1 and 5~20 mg·kg-1 significantly promoted an increase in photosynthetic pigments (P < 0.05). 4) Inhibition of the net photosynthetic rate increased with increasing Pb and Cd concentrations under both individual and combined stress. In addition, the root of D. involucrata had a strong absorption and fixation effect on heavy metals, thereby reducing metal toxicity and improving the tolerance of D. involucrata to heavy metals.

Quantitation of copper chlorophylls in green table olives by ultra-high-performance liquid chromatography with inductively coupled plasma isotope dilution mass spectrometry

Table olives, a widely consumed delicacy, are often selected by consumers based on the shade of their green color. The appealing coloration of fresh olives fades to brown or pale yellow during the industrial processing necessary for commercialization and storage, as a result of the degradation of chlorophyll a and b to their corresponding pheophytins and other chlorophyll degradation products (CDP). The re-greening of table olives may be achieved by complexation of CDP with Cu2+, to form stable bright green copper CDP (Cu-CDP) complexes. To study this phenomenon, we developed a novel method to separately extract lipophilic and hydrophilic Cu-CDP and quantify Cu-CDP by UHPLC combined with inductively coupled plasma isotope dilution mass spectrometry (UHPLC-ICP-ID-MS) using post-column isotopic dilution with 65Cu. This technique does not require species-specific calibration standards and was applied to survey the Cu-CDP composition of the various types of table olives sold in the US market. The CDP and Cu-CDP extracted from table olives were identified by high resolution full-scan mass spectrometry. Total elemental Cu in table olives was measured by microwave digestion followed by ICP-MS detection and correlated with the content of Cu-CDP. Pale yellow olives contained <1 mg/kg lipophilic Cu-CDP and <3.5 mg/kg total elemental Cu. Bright green table olives contained 4–22 mg/kg lipophilic Cu-CDP and 14.4–161 mg/kg total elemental Cu in contrast to <6 mg/kg reported for natural abundance, indicating the formation of Cu-CDP was achieved by addition of copper salts. A dark green sample with 2.5 mg/kg of total copper and 0.267 mg/kg lipophilic Cu-CDP may have been processed by addition of sodium copper chlorophyllin (SCC); the higher content of Cu isochlorin e4 compared to Cu 152-Me-chlorin e6 supports this conclusion.

Chlorophyll as key indicator to evaluate astaxanthin accumulation ability of Haematococcus pluvialis

BackgroundNatural astaxanthin is mainly derived from Haematococcus pluvialis. In the photoinduction phase, astaxanthin accumulation ability can be significantly affected by the characteristics of H. pluvialis cells in the proliferation phase. Based on sequential heterotrophy–dilution–photoinduction (SHDP) technology, the authors’ previous study showed that high astaxanthin accumulation ability is accompanied by high chlorophyll content of H. pluvialis heterotrophic cell; whereas the mechanism of this result remained largely obscure. Therefore, transcriptome analysis was conducted to explain this mechanism.ResultsRNA-seq analysis showed that the transcription level of chlorophyll synthesis-related genes was negatively correlated with genes related to astaxanthin synthesis. A metabolic network between chlorophyll synthesis and astaxanthin accumulation was proposed.ConclusionsThe relationship between chlorophyll synthesis and astaxanthin accumulation was clarified. Chlorophyll degradation products might be used for astaxanthin synthesis through certain pathways. This study enlightens on the mechanism for the transformation of pigment and is conducive to optimize culture process of H. pluvialis by improving the chlorophyll content of heterotrophic cell.

Strong correspondence between nitrogen isotope composition of foliage and chlorin across a rainfall gradient: implications for paleo-reconstruction of the nitrogen cycle

Abstract. Nitrogen (N) availability influences patterns of terrestrial productivity and global carbon cycling, imparting strong but poorly resolved feedbacks on Earth's climate system. Central questions concern the timescale of N cycle response to elevated CO2 concentration in the atmosphere and whether availability of this limiting nutrient increases or decreases with climate change. Nitrogen isotopic composition of bulk plant leaves provides information on large-scale patterns of N availability in the modern environment. Here we examine the utility of chlorins, degradation products of chlorophyll, hypothesized to persist in soil subsequent to plant decay, as proxies for reconstructing past plant δ15N. Specifically, we test the hypothesis that δ15N of plant leaves (δ15Nleaf) is recorded in δ15N of pheophytin a (δ15Npheo) along the leaf–litter–soil continuum across an array of ecosystem climate conditions and plant functional types (C3, C4, legumes, and woody plants). The δ15N of live foliage and bulk soil display marked declines with increasing rainfall, consistent with past studies in Hawaii and patterns worldwide. We find measurable chlorin concentrations along soil–depth profiles at all sites, with pheophytin a present in amounts required for isotopic analysis (&gt;10 nmol). δ15Npheo in leaves, litter, and soil track δ15Nleaf of plant leaves. We find potential for δ15Npheo records from soil to provide proxy information on δ15Nleaf.