Chlorophyll Breakdown Research Articles

Physiological Mechanism of Chlorophyll Breakdown for Leaves under Complete Submergence in Rice

Submergence‐tolerant rice (Oryza sativa L.) cultivars, including FR13A, retain green leaves for a longer duration than susceptible lines during submergence and exhibit prompt readaptation to the aerial environment after desubmergence. This study clarified the physiological mechanism responsible through the chlorophyll breakdown and photodamage in submerged rice leaves, as indicated by decrease in the maximal quantum yield of photosystem II (Fv/Fm). The ethylene‐releasing agent ethephon was used to evaluate the effect of ethylene on chlorophyll breakdown and plant growth. FR13A (submergence‐tolerant) and IR72442‐6B‐3‐2‐1‐1 (submergence‐susceptible), either treated with ethephon for 3 d before submergence or untreated, were submerged for 14 d. During submergence, the chlorophyll contents and Fv/Fm in the upper fully expanded leaf (fifth leaf) decreased earlier in IR72442 than in FR13A. The ethephon treatment accelerated the reduction of the Fv/Fm in the submerged fifth leaf of FR13A during submergence and inhibited recovery after desubmergence. The ethephon treatment reduced shoot biomass accumulation during and after submergence but had no effect on underwater shoot elongation in either cultivar. Therefore, photodamage was inhibited and high chlorophyll content was maintained in the submergence‐tolerant cultivar during submergence. The negative effects of ethylene in response to ethephon may be mediated by other mechanisms and not by an increase in shoot elongation.

Melatonin Improves the Photosynthetic Apparatus in Pea Leaves Stressed by Paraquat via Chlorophyll Breakdown Regulation and Its Accelerated de novo Synthesis.

The positive effect of melatonin on the function of the photosynthetic apparatus is known, but little is known about the specific mechanisms of melatonin's action in plants. The influence of melatonin on chlorophyll metabolism of 24-day-old Pisum sativum L. seedlings during paraquat (PQ)-induced oxidative stress was investigated in this study. Seeds were hydro-primed with water (H), 50 and 200 μM melatonin/water solutions (H-MEL50, H-MEL200), while non-primed seeds were used as controls (C). Increases in chlorophyllase activity (key enzyme in chlorophyll degradation) and 5-aminolevulinic acid contents (the first compound in the porphyrin synthesis pathway) were observed in H-MEL50 and H-MEL200 leaf disks. This suggests that melatonin may accelerate damaged chlorophyll breakdown and its de novo synthesis during the first hours of PQ treatment. Elevated level of pheophytin in control leaf disks following 24 h of PQ incubation probably was associated with an enhanced rate of chlorophyll degradation through formation of pheophytin as a chlorophyll derivative. This validates the hypothesis that chlorophyllide, considered for many years, as a first intermediate of chlorophyll breakdown is not. This is indicated by the almost unchanged chlorophyll to chlorophyllide ratio after 24 h of PQ treatment. However, prolonged effects of PQ-induced stress (48 h) revealed extensive discolouration of control and water-treated leaf disks, while melatonin treatment alleviated PQ-induced photobleaching. Also the ratio of chlorophyll to chlorophyllide and porphyrin contents were significantly higher in plants treated with melatonin, which may indicate that this indoleamine both retards chlorophyll breakdown and stimulates its de novo synthesis during extended stress. We concluded that melatonin added into the seeds enhances the ability of pea seedlings to accelerate chlorophyll breakdown and its de novo synthesis before stress appeared and for several hours after, while during prolonged PQ incubation melatonin delays chlorophyll degradation.

Over-expression of SlJA2 decreased heat tolerance of transgenic tobacco plants via salicylic acid pathway.

Over-expression of SlJA2 decreased the accumulation of SA, which resulted in significant physiological and gene expression changes in transgenic tobacco plants, leading to the decreased heat tolerance of transgenic tobacco. NAC family, the largest transcription factors in plants, responses to different environmental stimuli. Here, we isolated a typical NAC transcription factor (SlJA2) from tomato and got transgenic tobacco with SlJA2 over-expression. Expression of SlJA2 was induced by heat stress (42 °C), chilling stress (4 °C), drought stress, osmotic stress, abscisic acid, and salicylic acid. Over-expression of SlJA2 decreased the accumulation of salicylic acid by regulating expression of salicylic acid degradation gene under heat stress. Compared to WT plants, stomatal apertures and water loss increased in transgenic plants, and the damage of photosynthetic apparatus and chlorophyll breakdown were more serious in transgenic plants under heat stress. Meanwhile, more H2O2 and O2·- were accumulated transgenic plants and proline synthesis was restricted, which resulted in more serious oxidative damage compared to WT. qRT-PCR analysis showed that over-expression of SlJA2 could down-regulate genes involved in reactive oxygen species scavenging, proline biosynthesis, and response to heat stress. All the above results indicated that SlJA2 may be a negative regulator responded to plant's heat tolerance. Thus, this study provides new insight into roles of NAC family member in plant response to abiotic stress.

Plants water soluble chlorophyll binding proteins act as enzyme-inhibitor pair

The hydrophilic water-soluble chlorophyll binding proteins (WSCP) which form complex with chlorophyll molecules have been numerously isolated from the chloroplasts of plants. Although, their molecular properties have been partly characterized, but their physio-biochemical roles are still unclear in the photosynthesizing organs. In this study, using bioinformatic tools WSCP pair were predicted to act as hydrolase and hydrolase inhibitor towards chlorophyll molecules. To enhance our information regarding the possible functions of WSCP, we cloned WSCP1 and WSCP2 cDNAs from Chenopodium album L. and Brassica oleracea L. leaves and expressed them as soluble maltose-binding fusion proteins in Escherichia coli. The purified fused products were subjected to chlorophyll hydrolyzing activity in vitro. The results showed that WSCP1 and WCSP2 are antagonistically involved in chlorophyll breakdown, while WSCP1 acts as chlorophyll hydrolyzing enzyme (with the hydrolysis rate of about 40% per 12 h), WSCP2 exerts inhibitory activity (with the inhibition rate of about 38% per 12 h) towards chlorophyll hydrolysis. This is the first ever time report speculates the hydrolase/inhibitory roles for WSCP and proposes that the relative activity of WSCP pair might balance and regulate the chlorophyll breakdown process in the photosynthetic apparatus of plants. It may open the new gate to investigate the potent roles of WSCP in plant system.

Chlorophyll Binding Ability of Non-chloroplastic DUF538 Protein Superfamily in Plants

The type-1 water soluble chlorophyll binding proteins (WSCP1) have been generally known as chlorophyll extractors and transporters from the thylakoid membrane to the chloroplast envelope, where the membrane bound chlorophyllase catabolizes the chlorophyll. Despite the type-2 WSCP, WSCP1 has been known to be located in the chloroplasts of the green plants. In the present study, the non-chloroplastic protein superfamily containing domain of unknown function 538 (DUF538) as functional homologue of type-1 WSCP has been identified in plants. The structural similarities/differences and the cellular locations of Celosia cristata DUF538 and Chenopodium album WSCP1 were predicted by using computational tools and the chlorophyll binding abilities of their purified maltose binding protein-fused forms were estimated by maltose binding affinity method. It was predicted that despite CaWSCP1, CcDUF538 is a non-chloroplastic protein. The chlorophyll binding abilities of the recombinant fusion forms of test WSCP1 and DUF538 were estimated to be about 58 and 56%, respectively. Considering DUF538 as stress-induced protein, it was speculated that they may form complex with chlorophyll molecules or their hydrolyzed products out of chloroplasts to proceed the chlorophyll breakdown and nitrogen/carbon recycling in stress-challenged plants.

Identification of a Chlorophyll Dephytylase Involved in Chlorophyll Turnover in Arabidopsis.

Chlorophyll turns over in green organs during photosystem repair and is salvaged via de- and rephytylation, but the enzyme involved in dephytylation is unknown. We have identified an Arabidopsis thaliana thylakoid protein with a putative hydrolase domain that can dephytylate chlorophyll in vitro and in vivo. The corresponding locus, CHLOROPHYLL DEPHYTYLASE1 (CLD1), was identified by mapping a semidominant, heat-sensitive, missense allele (cld1-1). CLD1 is conserved in oxygenic photosynthetic organisms, sharing structural similarity with pheophytinase, which functions in chlorophyll breakdown during leaf senescence. Unlike pheophytinase, CLD1 is predominantly expressed in green organs and can dephytylate chlorophyll in vitro. The specific activity is significantly higher for the mutant protein encoded by cld1-1 than the wild-type enzyme, consistent with the semidominant nature of the cld1-1 mutation. Supraoptimal CLD1 activities in cld1-1 mutants and transgenic seedlings led to the proportional accumulation of chlorophyllides derived from chlorophyll dephytylation after heat shock, which resulted in light-dependent cotyledon bleaching. Reducing CLD1 expression diminished thermotolerance and the photochemical efficiency of photosystem II under prolonged moderate heat stress. Taken together, our results suggest that CLD1 is the long-sought enzyme for removing the phytol chain from chlorophyll during its turnover at steady state within the chloroplast.

Chlorophyll-Derived Yellow Phyllobilins of Higher Plants as Medium-Responsive Chiral Photoswitches.

The fall colors are signs of chlorophyll breakdown, the biological process in plants that generates phyllobilins. Most of the abundant natural phyllobilins are colorless, but yellow phyllobilins (phylloxanthobilins) also occur in fall leaves. As shown here, phylloxanthobilins are unique four‐stage photoswitches. Which switching mode is turned on is controlled by the molecular environment. In polar media, phylloxanthobilins are monomeric and undergo photoreversible Z/E isomerization, similar to that observed for bilirubin. Unlike bilirubin, however, the phylloxanthobilin Z isomers photodimerize in apolar solvents by regio‐ and stereospecific thermoreversible [2+2] cycloadditions from self‐assembled hydrogen‐bonded dimers. X‐ray analysis revealed the first stereostructure of a phylloxanthobilin and its hydrogen‐bonded self‐templating architecture, helping to rationalize its exceptional photoswitch features. The chemical behavior of phylloxanthobilins will play a seminal role in identifying biological roles of phyllobilins.

Nitric oxide triggers a transient metabolic reprogramming in Arabidopsis.

Nitric oxide (NO) regulates plant growth and development as well as responses to stress that enhanced its endogenous production. Arabidopsis plants exposed to a pulse of exogenous NO gas were used for untargeted global metabolomic analyses thus allowing the identification of metabolic processes affected by NO. At early time points after treatment, NO scavenged superoxide anion and induced the nitration and the S-nitrosylation of proteins. These events preceded an extensive though transient metabolic reprogramming at 6 h after NO treatment, which included enhanced levels of polyamines, lipid catabolism and accumulation of phospholipids, chlorophyll breakdown, protein and nucleic acid turnover and increased content of sugars. Accordingly, lipid-related structures such as root cell membranes and leaf cuticle altered their permeability upon NO treatment. Besides, NO-treated plants displayed degradation of starch granules, which is consistent with the increased sugar content observed in the metabolomic survey. The metabolic profile was restored to baseline levels at 24 h post-treatment, thus pointing up the plasticity of plant metabolism in response to nitroxidative stress conditions.

Characterization of a novel β-barrel protein (AtOM47) from the mitochondrial outer membrane of Arabidopsis thaliana.

In plant cells, mitochondria are major providers of energy and building blocks for growth and development as well as abiotic and biotic stress responses. They are encircled by two lipid membranes containing proteins that control mitochondrial function through the import of macromolecules and metabolites. Characterization of a novel β-barrel protein, OUTER MEMBRANE PROTEIN 47 (OM47), unique to the green lineage and related to the voltage-dependent anion channel (VDAC) protein family, showed that OM47 can complement a VDAC mutant in yeast. Mutation of OM47 in Arabidopsis thaliana by T-DNA insertion had no effect on the import of proteins, such as the β-barrel proteins translocase of the outer membrane 40 (TOM40) or sorting and assembly machinery 50 (SAM50), into mitochondria. Molecular and physiological analyses revealed a delay in chlorophyll breakdown, higher levels of starch, and a delay in the induction of senescence marker genes in the mutant lines. While there was a reduction of >90% in OM47 protein in mitochondria isolated from 3-week-old om47 mutants, in mitochondria isolated from 8-week-old plants OM47 levels were similar to that of the wild type. This recovery was achieved by an up-regulation of OM47 transcript abundance in the mutants. Combined, these results highlight a role in leaf senescence for this plant-specific β-barrel protein, probably mediating the recovery and recycling of chloroplast breakdown products by transporting metabolic intermediates into and out of mitochondria.

A Role for TIC55 as a Hydroxylase of Phyllobilins, the Products of Chlorophyll Breakdown during Plant Senescence.

Chlorophyll degradation is the most obvious hallmark of leaf senescence. Phyllobilins, linear tetrapyrroles that are derived from opening of the chlorin macrocycle by the Rieske-type oxygenase PHEOPHORBIDE a OXYGENASE (PAO), are the end products of chlorophyll degradation. Phyllobilins carry defined modifications at several peripheral positions within the tetrapyrrole backbone. While most of these modifications are species-specific, hydroxylation at the C32 position is commonly found in all species analyzed to date. We demonstrate that this hydroxylation occurs in senescent chloroplasts of Arabidopsis thaliana. Using bell pepper (Capsicum annuum) chromoplasts, we establish that phyllobilin hydroxylation is catalyzed by a membrane-bound, molecular oxygen-dependent, and ferredoxin-dependent activity. As these features resemble the requirements of PAO, we considered membrane-bound Rieske-type oxygenases as potential candidates. Analysis of mutants of the two Arabidopsis Rieske-type oxygenases (besides PAO) uncovered that phyllobilin hydroxylation depends on TRANSLOCON AT THE INNER CHLOROPLAST ENVELOPE55 (TIC55). Our work demonstrates a catalytic activity for TIC55, which in the past has been considered as a redox sensor of protein import into plastids. Given the wide evolutionary distribution of both PAO and TIC55, we consider that chlorophyll degradation likely coevolved with land plants.

A liquid chromatography-mass spectrometry platform for the analysis of phyllobilins, the major degradation products of chlorophyll in Arabidopsis thaliana.

During senescence, chlorophyll is broken down to a set of structurally similar, but distinct linear tetrapyrrolic compounds termed phyllobilins. Structure identification of phyllobilins from over a dozen plant species revealed that modifications at different peripheral positions may cause complex phyllobilin composition in a given species. For example, in Arabidopsis thaliana wild-type, eight different phyllobilins have structurally been characterized to date. Accurate phyllobilin identification and quantification, which classically have been performed by high performance liquid chromatography (HPLC) and UV/vis detection, are, however, hampered because of their similar physiochemical properties and vastly differing abundances in plant extracts. Here we established a rapid method for phyllobilin identification and quantification that couples ultra-HPLC with high-resolution/high-precision tandem mass spectrometry. Using Arabidopsis wild-type and mutant lines that are deficient in specific phyllobilin-modifying reactions, we identified a total of 16 phyllobilins, among them two that have not been described before in Arabidopsis. The single and collision-induced dissociation tandem mass spectrometry data of all 16 Arabidopsis phyllobilins were collected in a mass spectrometry library, which is available to the scientific community. The library allows rapid detection and quantification of phyllobilins within and across Arabidopsis genotypes and we demonstrate its potential use for high-throughput approaches and genome-wide association studies in chlorophyll breakdown. By extending the library with phyllobilin data from other plant species in the future, we aim providing a tool for chlorophyll metabolite analysis as a measure of senescence for practical applications, such as post-harvest quality control.

Salinity and ripening on/off the plant effects on lycopene synthesis and chlorophyll breakdown in hybrid Raf tomato

The aim of this study was to describe the physiology of fruit colour in tomato as affected by salinity and ripening on and off the plant. Chlorophyll and lycopene levels were repeatedly measured in ninety Raf tomatoes over a period of eight days using remittance spectroscopy. Fruits were subjected to three salinity levels and were measured either on or off the plant.The physiology of tomato colour was described by a kinetic model centred on the role of STAY-GREEN proteins (SGR) that was calibrated simultaneously on chlorophyll and lycopene data with a percentage variance explained for of 91%. Lycopene precursor and transcript SGR levels were estimated considerably higher for on-plant than for off-plant ripened fruits which indicates ongoing expression while attached to the plant. There is less inhibition of the lycopene precursor by SGR in on plant ripened tomatoes which results in higher maximum lycopene levels and less chlorophyll breakdown causing residual chlorophyll levels. Effects of salinity treatments on chlorophyll breakdown and lycopene synthesis are small, but higher salinity levels strongly diminish fresh weight. Ripening on and off the plant strongly affects colour physiology of tomato fruit and is described well by the proposed model.

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High hydrostatic pressure (HHP) has been widely used for producing plant-based food of fresh-like quality. In this study, HHP-induced changes in the spectral-optical properties of the chlorophyll pool was approached in climacteric tomato fruit. The pericarp in pre- and post ethylene production stages was treated with 250 MPa and 400 MPa at room temperature. The chlorophyll pool, consisting of chlorophyll a, chlorophyll b, and pheophytin, was measured at the Q band of chlorophyll absorption considering the spectral intensity at peak maximum (IPP) and the peak position (PP). The IPP remained unchanged after HHP treatments. This finding confirms earlier studies on the stable, total chlorophyll pool. The single chlorophyll types, however, were affected with decline of chlorophyll a and increase of pheophytin content, suggesting that HHP is enhancing the chlorophyll breakdown process. When comparing fruit developmental stages, the relatively enhanced pheophytin caused the observed bathochromic (red) shift of PP of the Q band. After HHP treatment, however, this effect was outweighed by a strong hypsochromic (blue) shift of PP, assumingly due to enhanced electron state when pigments were allocated out of the stable matrix. The strong hypsochromic shift of the Q band PP may serve as a non-destructively measurable, general variable for optimizing HHP conditions in climacteric fruit.

Chlorophyll catabolism in olive fruits (var. Arbequina and Hojiblanca) during maturation

The central reaction of chlorophyll (chl) breakdown pathway occurring during olive fruits maturation is the cleavage of the macrocycle pheophorbide a to a primary fluorescent chl catabolite (pFCC) and it is catalyzed by two enzymes: pheophorbide a oxygenase (PaO) and red chl catabolite reductase (RCCR). In subsequent steps, pFCC is converted to different fluorescent chlorophyll catabolites (FCCs) and nonfluorescent chlorophyll catabolites (NCCs). This work demonstrated that RCCR activity of olive fruits is type II. During the study of evolution of PaO and RCCR activities through the olive fruits maturation in two varieties: Hojiblanca and Arbequina, a significant increase in PaO and RCCR activity was found in ripening stage. In addition, the profile and structure of NCCs present in epicarp of this fruit was studied using HPLC/ESI-TOF-MS. Five different NCCs were defined and for the first time the enzymatic reactions implied in chlorophyll degradations in olive fruits elucidated.

High hydrostatic pressure effects on spectral-optical variables of the chlorophyll pool in climacteric fruit

High hydrostatic pressure (HHP) has been widely used for producing plant-based food of fresh-like quality. In this study, HHP-induced changes in the spectral-optical properties of the chlorophyll pool was approached in climacteric tomato fruit. The pericarp in pre- and post ethylene production stages was treated with 250 MPa and 400 MPa at room temperature. The chlorophyll pool, consisting of chlorophyll a, chlorophyll b, and pheophytin, was measured at the Q band of chlorophyll absorption considering the spectral intensity at peak maximum (IPP) and the peak position (PP). The IPP remained unchanged after HHP treatments. This finding confirms earlier studies on the stable, total chlorophyll pool. The single chlorophyll types, however, were affected with decline of chlorophyll a and increase of pheophytin content, suggesting that HHP is enhancing the chlorophyll breakdown process. When comparing fruit developmental stages, the relatively enhanced pheophytin caused the observed bathochromic (red) shift of PP of the Q band. After HHP treatment, however, this effect was outweighed by a strong hypsochromic (blue) shift of PP, assumingly due to enhanced electron state when pigments were allocated out of the stable matrix. The strong hypsochromic shift of the Q band PP may serve as a non-destructively measurable, general variable for optimizing HHP conditions in climacteric fruit.

ChemInform Abstract: Breakdown of Chlorophyll in Higher Plants—Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death

AbstractReview: [126 refs.

Effect of modified atmosphere packaging (MAP) on rachis quality of ‘Red Globe’ table grape variety

Rachis browning corresponds to a postharvest disorder that drastically reduces overall table grape quality. This problem has been associated mainly to water loss, but the possibility of having other factors involved like green pigment degradation and brownish compound synthesis that mask the green tissue is also feasible. Modified Atmosphere Packaging (MAP) is a technology used to extend table grape postharvest life, including rachis appearance. The objective of this study was to analyze the effects caused by MAP on rachis browning during cold storage of ‘Red Globe’ table grape variety. MAP helped to reduce the green color loss on rachises stored for 90days of storage at 0°C compared with a conventional storage (CS) even after a shelf life period, without to affect negatively the quality of the berries. Interestingly, MAP storage decreased the content of chlorophyll-a and increased the amount of pheophytin-a, a chlorophyll degradation product, compared to CS both after cold storage period and shelf life. Additionally, the expression of genes involved in the chlorophyll breakdown pathway was analyzed by qPCR. We found that MAP induced an increase in the transcript abundance of metal-chelating substance (MCS) and Red Chlorophyll Catabolite Reductase (RCCR) genes. However, Pheophytinase (PPH) and Pheophorbide-a Oxigenase (PaO) transcript accumulation revealed no changes compared with CS. Apparently, MAP generated a modification in the chlorophyll breakdown process allowing an accumulation of green like compounds responsible for the greener color of rachises in the MAP stored bunches. On the other hand, histological analysis reveals that after cold storage and shelf life, morphological changes and brown compounds accumulation take place at the periderm and cortex tissues, and these symptoms are less severe in MAP stored bunches helping to keep longer the green coloration of the rachises. In this study we observed that MAP storage increases rachis postharvest quality by reducing green color loss probably due to a combination of processes involving a delay of green pigments degradation and a less accumulation of brown compounds at the periderm and cortex tissues, thus preventing green pigments masking.

Proteome changes in banana fruit peel tissue in response to ethylene and high-temperature treatments.

Banana (Musa AAA group) is one of the most consumed fruits in the world due to its flavor and nutritional value. As a typical climacteric fruit, banana responds to ethylene treatment, which induces rapid changes of color, flavor (aroma and taste), sweetness and nutritional composition. It has also been reported that ripening bananas at temperatures above 24 °C inhibits chlorophyll breakdown and color formation but increases the rate of senescence. To gain fundamental knowledge about the effects of high temperature and ethylene on banana ripening, a quantitative proteomic study employing multiplex peptide stable isotope dimethyl labeling was conducted. In this study, green (immature) untreated banana fruit were subjected to treatment with 10 μL L−1 of ethylene for 24 h. After ethylene treatment, treated and untreated fruit were stored at 20 or 30 °C for 24 h. Fruit peel tissues were then sampled after 0 and 1 day of storage, and peel color and chlorophyll fluorescence were evaluated. Quantitative proteomic analysis was conducted on the fruit peels after 1 day of storage. In total, 413 common proteins were identified and quantified from two biological replicates. Among these proteins, 91 changed significantly in response to ethylene and high-temperature treatments. Cluster analysis on these 91 proteins identified 7 groups of changed proteins. Ethylene treatment and storage at 20 °C induced 40 proteins that are correlated with pathogen resistance, cell wall metabolism, ethylene biosynthesis, allergens and ribosomal proteins, and it repressed 36 proteins that are associated with fatty acid and lipid metabolism, redox–oxidative responses, and protein biosynthesis and modification. Ethylene treatment and storage at 30 °C induced 32 proteins, which were mainly similar to those in group 1 but also included 8 proteins in group 3 (identified as chitinase, cinnamyl alcohol dehydrogenase 1, cysteine synthase, villin-2, leucine-transfer RNA ligase, CP47 protein and calmodulin) and repressed 43 proteins in 4 groups (groups 4–7), of which 6 were associated with photosynthesis II oxygen-evolving protein, the photosynthesis I reaction center, sugar metabolism, the redox–oxidative system and fatty acid metabolism. Differences in the response to ethylene and holding temperature at 30 °C were also revealed and have been discussed. The identities and quantities of the proteins found were linked with quality changes. This study demonstrates that ethylene and high temperature influence banana fruit ripening and senescence at the proteomic level and reveals the mechanisms by which high temperature accelerates banana fruit ripening.

Crystal structure of methylesterase family member 16 (MES16) from Arabidopsis thaliana

Methylesterase family member 16 (MES16) is an integral component of chlorophyll breakdown. It catalyzes the demethylation of fluorescent chlorophyll catabolite (FCC) and pheophorbide in vitro, and specifically demethylates FCC in vivo. Here we report the crystal structure of MES16 from Arabidopsis thaliana at 2.8 Å resolution. The structure confirm that MES16 is a member of the α/β-hydrolase superfamily with Ser-87, His-239, and Asp-211 as the catalytic triad. Our biochemical studies reveal that MES16 has esterase activity with methyl-indole acetic acid as the substrate, and the catalytically essential role of Ser-87 has been demonstrated.

Breakdown of Chlorophyll in Higher Plants--Phyllobilins as Abundant, Yet Hardly Visible Signs of Ripening, Senescence, and Cell Death.

Fall colors have always been fascinating and are still a remarkably puzzling phenomenon associated with the breakdown of chlorophyll (Chl) in leaves. As discovered in recent years, nongreen bilin‐type Chl catabolites are generated, which are known as the phyllobilins. Collaborative chemical‐biological efforts have led to the elucidation of the key Chl‐breakdown processes in senescent leaves and in ripening fruit. Colorless and largely photoinactive phyllobilins are rapidly produced from Chl, apparently primarily as part of a detoxification program. However, fluorescent Chl catabolites accumulate in some senescent leaves and in peels of ripe bananas and induce a striking blue glow. The structural features, chemical properties, and abundance of the phyllobilins in the biosphere suggest biological roles, which still remain to be elucidated.