Chlorophyll Breakdown Research Articles

Residual nitrogen pools in mature winter wheat straw as affected by nitrogen application

Reduction of the amount of nitrogen (N) remaining in mature wheat straw is an essential challenge in order to boost grain protein and N use efficiency. However, very limited information is available on the composition of the residual N pools and how they are affected by N fertilization. Winter wheat was grown under field conditions at five different N levels ranging from 60 to 280 kg N ha−1. The fraction of straw N present in amino acids, chlorophyll, DNA, nitrate and lignin-associated compounds were analyzed separately in leaf blades, sheaths and stems. Total straw N concentration increased from 0.29 to 0.69% with increasing level of N application. The largest N pool consisted of amino acids in hydrolysable proteins, which comprised 50 to 70% of the residual N. Lignin-associated, non-hydrolysable N compounds constituted 13 to 16% of the total N, while non-protein N pools (mainly chlorophyll breakdown products and DNA) amounted to 5–14%. Protein-derived amino acids constituted the most abundant N pool in mature wheat straw. Despite a 2.5-fold increase in total straw N content, the relative proportion of the different residual N pools to the total N content in the straw did not change with N fertilization.

Advancement of research on post harvest management of fruit crops

After harvest, the plant organs undergo several physiological, biochemical and biological processes affecting the quality of the products. In addition, the environmental and biotic factors affect fruit qualities. The metabolic activity of harvested plant organs differs depending on species or cultivars. Immediately after harvest, senescence starts and secondary metabolic activity leads to some catabolic processes. These metabolic changes during the post-harvest period involve as plant pigment changes (biosynthesis of lycopene and breakdown of chlorophyll) and browning reactions (biosynthesis of phenolic substances). Post-harvest secondary metabolism is also influenced by exogenous factors such as temperature or storage atmosphere, and ethylene as the main endogenous factor. The aim of this article is to provide information on the post harvest management of some fruits for those people who are dealing with the storage of fruits.

Endogenous ascorbic acid delays ethylene-induced leaf senescence in Arabidopsis thaliana

Leaf senescence is an important event in the plant life cycle. Ethylene and ascorbic acid (AsA) both regulate the leaf senescence process. The role of endogenous AsA in ethylene-induced leaf senescence was explored in two independent endogenous AsA changing Arabidopsis thaliana mutants. The line vtc2-1 with a single base change in VTC was AsA-deficient mutant; the GLDH-overexpressing line (GLDHOE) driven by the CaMV 35S promoter was AsA-overaccumulating mutant. After spraying 600 μM ethephon for 6 d, vtc2-1 showed the most serious leaf chlorosis, reactive oxygen species (ROS) accumulation, chlorophyll breakdown, Rubisco degradation, and had the highest expression level of senescence-associated genes (SAGs), such as SAG12, SAG13, SAG20, and SAG21 among the three lines. In contrast, GLDHOE maintained the highest photosynthetic pigments contents, Rubisco content, antioxidant capacity, and the lowest expression of SAG2, SAG20, and SAG21 among the three lines. Taken together, we conclude that endogenous AsA can delay ethylene-induced senescence by scavenging ROS and inhibiting SAGs expression.

Pheophorbide a: State of the Art.

Chlorophyll breakdown products are usually studied for their antioxidant and anti-inflammatory activities. The chlorophyll derivative Pheophorbide a (PPBa) is a photosensitizer that can induce significant anti-proliferative effects in several human cancer cell lines. Cancer is a leading cause of death worldwide, accounting for about 9.6 million deaths, in 2018 alone. Hence, it is crucial to monitor emergent compounds that show significant anticancer activity and advance them into clinical trials. In this review, we analyze the anticancer activity of PPBa with or without photodynamic therapy and also conjugated with or without other chemotherapic drugs, highlighting the capacity of PPBa to overcome multidrug resistance. We also report other activities of PPBa and different pathways that it can activate, showing its possible applications for the treatment of human pathologies.

The red chlorophyll catabolite (RCC) is an inefficient sensitizer of singlet oxygen - photochemical studies of the methyl ester of RCC.

The red chlorophyll catabolite (RCC) is a proposed cryptic intermediate of chlorophyll (Chl) breakdown in higher plants. Its accumulation in higher plants is believed to be metabolically suppressed, as RCC is commonly suspected to efficiently sensitize for the formation of the cell poison singlet oxygen (1O2). We report here a study on luminescence of the methyl ester of RCC (Me-RCC) and of its capacity to generate 1O2 in ethanolic solution. A solution of Me-RCC fluoresces at room temperature with a maximum near 670 nm and features a fluorescence spectrum with pronounced vibrational spacing at 77 K. As shown here, sensitization of the generation of 1O2 by Me-RCC in an oxygen-saturated solution in hexadeutero-ethanol occurs with a maximal quantum yield of only about 0.015. This low quantum yield suggests that the specific catabolic suppression of the accumulation of RCC during Chl breakdown is not primarily a countermeasure against the formation of 1O2 by RCC in the plant, but has other crucial reasons mainly.

Rice (Oryza sativa) Receptor for Activated C Kinase1B (OsRACK1B) Regulates Chlorophyll Catabolism and NADPH oxidase‐dependent H2O2 Signaling Pathways during Salinity Stress

The Receptor for Activated C Kinase1B (RACK1B) is a WD‐40 type scaffold protein that regulates diverse environmental stress signal transduction pathways. Arabidopsis RACK1A has been reported to interact with various proteins in salt stress and Light‐Harvesting Complex (LHC) pathways. However, the mechanism of how RACK1 contributes to the photosystem and chlorophyll metabolism in stress conditions remains elusive. Using T‐DNA‐mediated activation tagging transgenic rice (Oryza sativa L.) lines, we show that leaves from rice RACK1B gene (OsRACK1B) gain‐of‐function (OsRACK1B‐OX) plants exhibit the stay‐green phenotype by stabilizing chlorophyll under salinity stress. In contrast, leaves from down‐regulated OsRACK1B (OsRACK1B‐UX) plants display an accelerated yellowing phenotype accompanied by chlorophyll degradation. qRT‐PCR analysis revealed that genes encoding chlorophyll catabolic enzymes (CCEs) are differentially expressed in both OsRACK1B‐OX and OsRACK1B‐UX rice plants. In addition to CCEs, STAY‐GREEN (SGR) is a key component that forms the SGR‐CCE complex in senescing chloroplasts, which causes LHCII complex instability. Transcript and protein profiling revealed a significant upregulation of OsSGR in RACK1B‐UX plants than that in RACK1B‐OX plants during salt stress. The BiFC assay demonstrated that OsRACK1B interacts with OsSGR in planta in both cytoplasm and the nucleus. Our findings suggest that overexpression of OsRACK1B negatively regulates chlorophyll degradation, delays salinity‐induced senescence and OsRACK1B functions in this process, at least in part, by antagonizing the function of OsSGR through a direct interaction. Interestingly, histochemical staining revealed a global increase of hydrogen peroxide (H2O2) in plants overexpressing OsRACK1B compared to that of the wild‐type and the trend can be reversed by pre‐treatment leaves with diphenylidonium (DPI), a NADPH oxidase (NOX) inhibitor. In gel‐activity of NOX and Reactive Oxygen Species (ROS) scavenging enzymes revealed that OsRACK1B regulates NOX and ROS scavenging enzyme activity in a salt stress dependent manner indicating a complex interplay and a novel regulatory module involving OsRACK1, NOX dependent H2O2 signaling, and a balanced ROS scavenging enzyme activity. BiFC analysis demonstrated that RACK1 also interacts with N‐terminal region of NOX at the plasma membrane. We hypothesize that elevated level of H2O2 acts as a signaling molecule to counteract salt stress and chlorophyll catabolism in OsRACK1B transgenic leaves under salinity stress. Taken together, these results provide important insights into the molecular mechanisms of chlorophyll catabolism, salinity‐induced senescence which can be useful in circumventing the effect of salt on photosynthesis and in reducing yield penalty of important cereal crops, like rice, in global climate change conditions.Support or Funding InformationThis work was partially supported by National Science Foundation (NSF), USA grant to Howard University (Grant number MCB 0542312); Dept. of Biology and Graduate School of the Howard University.Proposed working model of how OsRACK1B delays chlorophyll breakdown through regulation of Stay‐Green (SGR) protein and Rboh/NADPH‐Oxidase‐dependent H2O2 signaling to cope with high salinity stress.OsRACK1B localizes in the nucleus and the cytoplasm in rice. During abiotic stresses such as high salinity, OsRACK1B directly or indirectly represses the transcripts of chlorophyll catabolic genes and activates defense‐related genes in the nucleus. After synthesized in the cytosol, OsRACK1B shuttles to the chloroplast where it binds to the Stay‐Green (SGR) protein and limits the availability of SGR to form SGR‐CCE‐LHCII multi‐protein complex, a prerequisite for chlorophyll breakdown. Simultaneously, OsRACK1B interacts with the N‐terminal region of Rboh/NADPH oxidase in the cytoplasm and regulates the NADPH oxidase‐dependent H2O2 production via the action of CuZn‐SOD resulting in a ROS dependent systemic wave inside the cell. At a certain level, H2O2 can act as a signaling molecule to generate a positive feedback loop for chloroplast homeostasis and may trigger retrograde signaling to regulate nuclear gene expression to protect the chloroplast and enhance stress tolerance of the plant. High salinity stress also induces stress phytohormone abscisic acid (ABA). OsRACK1B can also protect the photosystem complex through negative regulation of ABA signaling pathway. Solid and dotted lines indicate actual and hypothetical regulations of the signaling effect, respectively.Figure 1

Comparative Proteomic Analysis by iTRAQ Reveals that Plastid Pigment Metabolism Contributes to Leaf Color Changes in Tobacco (Nicotiana tabacum) during Curing.

Tobacco (Nicotiana tabacum), is a world’s major non-food agricultural crop widely cultivated for its economic value. Among several color change associated biological processes, plastid pigment metabolism is of trivial importance in postharvest plant organs during curing and storage. However, the molecular mechanisms involved in carotenoid and chlorophyll metabolism, as well as color change in tobacco leaves during curing, need further elaboration. Here, proteomic analysis at different curing stages (0 h, 48 h, 72 h) was performed in tobacco cv. Bi’na1 with an aim to investigate the molecular mechanisms of pigment metabolism in tobacco leaves as revealed by the iTRAQ proteomic approach. Our results displayed significant differences in leaf color parameters and ultrastructural fingerprints that indicate an acceleration of chloroplast disintegration and promotion of pigment degradation in tobacco leaves due to curing. In total, 5931 proteins were identified, of which 923 (450 up-regulated, 452 down-regulated, and 21 common) differentially expressed proteins (DEPs) were obtained from tobacco leaves. To elucidate the molecular mechanisms of pigment metabolism and color change, 19 DEPs involved in carotenoid metabolism and 12 DEPs related to chlorophyll metabolism were screened. The results exhibited the complex regulation of DEPs in carotenoid metabolism, a negative regulation in chlorophyll biosynthesis, and a positive regulation in chlorophyll breakdown, which delayed the degradation of xanthophylls and accelerated the breakdown of chlorophylls, promoting the formation of yellow color during curing. Particularly, the up-regulation of the chlorophyllase-1-like isoform X2 was the key protein regulatory mechanism responsible for chlorophyll metabolism and color change. The expression pattern of 8 genes was consistent with the iTRAQ data. These results not only provide new insights into pigment metabolism and color change underlying the postharvest physiological regulatory networks in plants, but also a broader perspective, which prompts us to pay attention to further screen key proteins in tobacco leaves during curing.

Post-translational coordination of chlorophyll biosynthesis and breakdown by BCMs maintains chlorophyll homeostasis during leaf development

Chlorophyll is indispensable for life on Earth. Dynamic control of chlorophyll level, determined by the relative rates of chlorophyll anabolism and catabolism, ensures optimal photosynthesis and plant fitness. How plants post-translationally coordinate these two antagonistic pathways during their lifespan remains enigmatic. Here, we show that two Arabidopsis paralogs of BALANCE of CHLOROPHYLL METABOLISM (BCM) act as functionally conserved scaffold proteins to regulate the trade-off between chlorophyll synthesis and breakdown. During early leaf development, BCM1 interacts with GENOMES UNCOUPLED 4 to stimulate Mg-chelatase activity, thus optimizing chlorophyll synthesis. Meanwhile, BCM1’s interaction with Mg-dechelatase promotes degradation of the latter, thereby preventing chlorophyll degradation. At the onset of leaf senescence, BCM2 is up-regulated relative to BCM1, and plays a conserved role in attenuating chlorophyll degradation. These results support a model in which post-translational regulators promote chlorophyll homeostasis by adjusting the balance between chlorophyll biosynthesis and breakdown during leaf development.

Rice Senescence-Induced Receptor-Like Kinase (OsSRLK) Is Involved in Phytohormone-Mediated Chlorophyll Degradation.

Chlorophyll breakdown is a vital catabolic process of leaf senescence as it allows the recycling of nitrogen and other nutrients. In the present study, we isolated rice senescence-induced receptor-like kinase (OsSRLK), whose transcription was upregulated in senescing rice leaves. The detached leaves of ossrlk mutant (ossrlk) contained more green pigment than those of the wild type (WT) during dark-induced senescence (DIS). HPLC and immunoblot assay revealed that degradation of chlorophyll and photosystem II proteins was repressed in ossrlk during DIS. Furthermore, ultrastructural analysis revealed that ossrlk leaves maintained the chloroplast structure with intact grana stacks during dark incubation; however, the retained green color and preserved chloroplast structures of ossrlk did not enhance the photosynthetic competence during age-dependent senescence in autumn. In ossrlk, the panicles per plant was increased and the spikelets per panicle were reduced, resulting in similar grain productivity between WT and ossrlk. By transcriptome analysis using RNA sequencing, genes related to phytohormone, senescence, and chlorophyll biogenesis were significantly altered in ossrlk compared to those in WT during DIS. Collectively, our findings indicate that OsSRLK may degrade chlorophyll by participating in a phytohormone-mediated pathway.

The novel protein CSAP accelerates leaf senescence and is negatively regulated by SAUL1 in the dark.

The chloroplast-localized protein CSAP is an ABA-responsive factor and positively regulates dark-induced senescence. This phenomenon is controlled by SAUL1 in Arabidopsis. We report here that CSAP (Chloroplast-localized Senescence-Associated Protein, AT5G39520) functions as a positive regulator of senescence and is controlled by SAUL1 (Senescence Associated E3 Ubiquitin Ligase 1) in Arabidopsis. CSAP transcript level was gradually increased when senescence was progressed. Under dark conditions, the csap mutant showed delayed leaf senescence and reduced chlorophyll breakdown, but overexpression of CSAP accelerated leaf senescence and expressions of chlorophyll catabolic genes were up-regulated compared to the wild-type (WT). NCED3 and AAO3, which are involved in ABA biosynthesis, also showed higher expression in the overexpression lines than the WT. It is known that the CSAP transcript is increased in the saul1 mutant that shows precocious senescence. In our experiments, we confirmed that CSAP interacts with SAUL1 by the yeast two-hybrid and pull-down assays. In addition, we found that SAUL1 decreases the stability of CSAP in the presence of ABA. Taken together, we suggest that CSAP accelerates leaf senescence in the dark and this process is controlled by SAUL1.

Pheophorbide a May Regulate Jasmonate Signaling during Dark-Induced Senescence.

Chlorophyll degradation is one of the most visible signs of leaf senescence. During senescence, chlorophyll is degraded in the multistep pheophorbide a oxygenase (PAO)/phyllobilin pathway. This pathway is tightly regulated at the transcriptional level, allowing coordinated and efficient remobilization of nitrogen toward sink organs. Using a combination of transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis (Arabidopsis thaliana) mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. pheophorbide a Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, a mutant deficient in PAO. We propose that pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and a unique pathway "bottleneck," has been recruited as a signaling molecule of chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a result of senescence, and proposes that the flux of pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves.

Lipid remodeling regulator 1 (LRL1) is differently involved in the phosphorus-depletion response from PSR1 in Chlamydomonas reinhardtii.

SummaryThe elucidation of lipid metabolism in microalgae has attracted broad interest, as their storage lipid, triacylglycerol (TAG), can be readily converted into biofuel via transesterification. TAG accumulates in the form of oil droplets, especially when cells undergo nutrient deprivation, such as for nitrogen (N), phosphorus (P), or sulfur (S). TAG biosynthesis under N‐deprivation has been comprehensively studied in the model microalga Chlamydomonas reinhardtii, during which TAG accumulates dramatically. However, the resulting rapid breakdown of chlorophyll restricts overall oil yield productivity and causes cessation of cell growth. In contrast, P‐deprivation results in oil accumulation without disrupting chloroplast integrity. We used a reverse genetics approach based on co‐expression analysis to identify a transcription factor (TF) that is upregulated under P‐depleted conditions. Transcriptomic analysis revealed that the mutants showed repression of genes typically associated with lipid remodeling under P‐depleted conditions, such as sulfoquinovosyl diacylglycerol 2 (SQD2), diacylglycerol acyltransferase (DGTT1), and major lipid droplet protein (MLDP). As accumulation of sulfoquinovosyl diacylglycerol and TAG were suppressed in P‐depleted mutants, we designated the protein as lipid remodeling regulator 1 (LRL1). LRL1 mutants showed slower growth under P‐depletion. Moreover, cell size in the mutant was significantly reduced, and TAG and starch accumulation per cell were decreased. Transcriptomic analysis also suggested the repression of several genes typically upregulated in adaptation to P‐depletion that are associated with the cell cycle and P and lipid metabolism. Thus, our analysis of LRL1 provides insights into P‐allocation and lipid remodeling under P‐depleted conditions in C. reinhardtii.Open Research Badges This article has earned an Open Data Badge for making publicly available the digitally‐shareable data necessary to reproduce the reported results. The sequencing data were made publicly available under the BioProject Accession number PRJDB6733 and an accession number LC488724 at the DNA Data Bank of Japan (DDBJ). The data is available at https://trace.ddbj.nig.ac.jp/BPSearch/bioproject?acc=PRJDB6733; http://getentry.ddbj.nig.ac.jp/getentry/na/LC488724. The metabolome data were made publicly available and can be accessed at http://metabolonote.kazusa.or.jp/SE195:/; http://webs2.kazusa.or.jp/data/nur/.

Transcriptional Reprogramming of Pea Leaves at Early Reproductive Stages.

Pea (Pisum sativum L.) is an important source of dietary proteins. Nutrient recycling from leaves contributes to the accumulation of seed proteins and is a pivotal determinant of protein yields in this grain legume. The aim of this study was to unveil the transcriptional regulations occurring in pea leaves before the sharp decrease in chlorophyll breakdown. As a prelude to this study, a time-series analysis of 15N translocation at the whole plant level was performed, which indicated that nitrogen recycling among organs was highly dynamic during this period and varied depending on nitrate availability. Leaves collected on vegetative and reproductive nodes were further analyzed by transcriptomics. The data revealed extensive transcriptome changes in leaves of reproductive nodes during early seed development (from flowering to 14 days after flowering), including an up-regulation of genes encoding transporters, and particularly of sulfate that might sustain sulfur metabolism in leaves of the reproductive part. This developmental period was also characterized by a down-regulation of cell wall-associated genes in leaves of both reproductive and vegetative nodes, reflecting a shift in cell wall structure. Later on, 27 days after flowering, genes potentially switching the metabolism of leaves toward senescence were pinpointed, some of which are related to ribosomal RNA processing, autophagy, or transport systems. Transcription factors differentially regulated in leaves between stages were identified and a gene co-expression network pointed out some of them as potential regulators of the above-mentioned biological processes. The same approach was conducted in Medicago truncatula to identify shared regulations with this wild legume species. Altogether the results give a global view of transcriptional events in leaves of legumes at early reproductive stages and provide a valuable resource of candidate genes that could be targeted by reverse genetics to improve nutrient remobilization and/or delay catabolic processes leading to senescence.

Chlorine dioxide delays the reddening of postharvest green peppers by affecting the chlorophyll degradation and carotenoid synthesis pathways

The change in colour from green to red, known as reddening, is a major problem in green pepper cultivation, implying ripening and senescence. Chlorine dioxide (ClO2) is used to preserve the quality of vegetables and fruits because of its safety. In this work, the effects of ClO2 on reddening in green peppers, their chlorophyll and carotenoid content, and the molecular mechanisms involved are studied. The results show that 30 μL L−1 of ClO2 treatment reduced the reddening rate markedly compared to the control. ClO2 delayed the degradation of chlorophyll and significantly reduced the synthesis of capsanthin and β-carotene. Additionally, the transcript levels of pheophytin pheophorbide hydrolase (PPH), pheophorbide a oxygenase (PAO), and red chlorophyll catabolite reductase (RCCR) genes, associated with chlorophyll breakdown, were inhibited by ClO2 treatment, and the relative expression of phytoene synthase (Psy), lycopene β-cyclase enzyme (Lcyb), capsanthin/capsorubin synthase (Ccs), and β-carotene hydroxygenase enzyme (Crtz) genes, associated with carotenoid synthesis, were suppressed. These findings indicate that ClO2 delayed reddening by suppressing the expression of certain genes associated with chlorophyll breakdown and carotenoid synthesis in harvested green peppers.

The occurrence of red and yellow autumn leaves explained by regional differences in insolation and temperature.

Red or yellow autumn leaves have long fascinated biologists, but their geographical concentration in trees in Eastern North America (ENA) has defied evolutionary explanations. In this review, anthocyanins and xanthophylls are discussed in relation to their occurrence in different regions of the Northern Hemisphere, phylogenetic distribution and photoprotective function during the breakdown of chlorophylls. Pigments in senescing leaves that intercept incident light and dissipate the absorbed energy extend the time available for nutrient resorption. Experiments with Arabidopsis have revealed greatest anthocyanin photoprotective function at low temperatures and high light intensities, and high-resolution solar irradiation maps reveal that ENA and Asia receive higher irradiation than does Europe. In addition, ENA experiences higher temperature fluctuations in autumn, resulting in cold snaps during leaf senescence. Under common garden conditions, chlorophyll degradation occurs earlier in ENA species than in their European and East Asian relatives. In combination, strong solar irradiation, temperature fluctuations and, on average, 3-wk shorter vegetation periods of ENA species favour investment in pigments to extend the time for nutrient resorption before abscission, explaining the higher frequency of coloured species in ENA compared to Europe. We end by outlining research that could test this new explanation of bright New England autumns.

Cryptic chlorophyll breakdown in non-senescent green Arabidopsis thaliana leaves.

Chlorophyll (Chl) breakdown is a diagnostic visual process of leaf senescence, which furnishes phyllobilins (PBs) by the PAO/phyllobilin pathway. As Chl breakdown disables photosynthesis, it appears to have no role in photoactive green leaves. Here, colorless PBs were detected in green, non-senescent leaves of Arabidopsis thaliana. The PBs from the green leaves had structures entirely consistent with the PAO/phyllobilin pathway and the mutation of a single Chl catabolic enzyme completely abolished PBs with the particular modification. Hence, the PAO/phyllobilin pathway was active in the absence of visible senescence and expression of genes encoding Chl catabolic enzymes was observed in green Arabidopsis leaves. PBs accumulated to only sub-% amounts compared to the Chls present in the green leaves, excluding a substantial contribution of Chl breakdown from rapid Chl turnover associated with photosystem II repair. Indeed, Chl turnover was shown to involve a Chl a dephytylation and Chl a reconstitution cycle. However, non-recyclable pheophytin a is also liberated in the course of photosystem II repair, and is proposed here to be scavenged and degraded to the observed PBs. Hence, a cryptic form of the established pathway of Chl breakdown is indicated to play a constitutive role in photoactive leaves.

Biochemical and physiological aspects of chlorophyll breakdown

During leaf senescence and fruit ripening chlorophyll is broken down into nonfluorescent catabolites (NCCs). The chlorophyll degradation pathway includes a series of biochemical transformations ocurring sequentially in chloroplasts, cytosol and vacuoles. The path begins with enzymatic reduction of chlorophyll b to chlorophyll a. Next, the specific dechelatase and esterase remove the magnesium atom and the phytol chain resulting in the formation of pheophorbide a. In the next step, the porphyrin macroring is opened by pheophorbide a oxygenase and red catabolite reductase. The product of this transformation is an early fluorescent catabolite (pFCC), which after hydroxylation and species-specific modifications is imported into the vacuole. In acidic medium of the vacuole pFCC undergo isomerization to their respective colorless NCCs, which are final chlorophyll degradation products in higher plants. There are still no answers to a number of questions about the fate and significance of millions tons of chlorophyll catabolites released annually in the aquatic environment as a result of cellular senescence and death of phytoplankton. A few reports indicate that algae and cyanobacteria may metabolize their photosynthetic pigments in a similar way as higher plants do, however, the course of chlorophyll breakdown in these organisms has not been yet elucidated.

A pink colored dioxobilin-type phyllobilin from breakdown of chlorophyll

In senescent leaves of higher plants, colorless chlorophyll (Chl) catabolites typically accumulate that belong to one of two major types, classified as formyloxobilin-type or dioxobilin-type phyllobilins (PBs). Natural yellow and pink colored formyloxobilin-type PBs are also known, named YCCs and PiCCs, respectively. A dioxobilin-type yellow Chl catabolite (DYCC) was recently prepared by partial synthesis, characterized by spectroscopic means and also identified in grapevine leaves. Here, we report the first dioxobilin-type pink Chl catabolite (DPiCC) from its partial synthesis from the DYCC. The DPiCC had similar structural features and absorption characteristics (in the visible spectral region) as the natural PiCC, its formyloxobilin-type analogon. In contrast to the effectively racemic PiCC, the DPiCC is an optically active pigment with a stable new asymmetric carbon center.Graphical abstract

In Search of Bioactivity - Phyllobilins, an Unexplored Class of Abundant Heterocyclic Plant Metabolites from Breakdown of Chlorophyll.

The fate of the green plant pigment chlorophyll (Chl) in de‐greening leaves has long been a fascinating biological puzzle. In the course of the last three decades, various bilin‐type products of Chl breakdown have been identified, named phyllobilins (PBs). Considered ‘mere’ leftovers of a controlled biological Chl detoxification originally, the quest for finding relevant bioactivities of the PBs has become a new paradigm. Indeed, the PBs are abundant in senescent leaves, in ripe fruit and in some vegetables, and they display an exciting array of diverse heterocyclic structures. This review outlines briefly which types of Chl breakdown products occur in higher plants, describes basics of their bio‐relevant structural and chemical properties and gives suggestions as to ‘why’ the plants produce vast amounts of uniquely ‘decorated’ heterocyclic compounds. Clearly, it is worthwhile to consider crucial metabolic roles of PBs in plants, which may have practical consequences in agriculture and horticulture. However, PBs are also part of our plant‐based nutrition and their physiological and pharmacological effects in humans are of interest, as well.

Catabolism and bioactive properties of chlorophylls

Chlorophylls are fundamental molecules for life and probably the most important of all natural pigments. Although chlorophyll breakdown is inevitably associated with the loss of green color during ripening or senescence, the truth is that chlorophyll molecules continuously degrade through so-called chlorophyll turnover (lifetime of hours). In addition to their primary function, chlorophylls are in demand due to their bioactive properties. Recently, several chlorophyll derivatives have shown health promoting activities. This review also provides an updated outline of the most recent advances that have occurred in the deciphering mechanism of chlorophyll catabolism; it will also describe the novel biological properties associated with chlorophyll derivatives.