Pathway Of Chlorophyll Breakdown Research Articles

Poplar leaf abscission through induced chlorophyll breakdown by Mg-dechelatase

Chlorophyll breakdown is observed during senescence. The first step in chlorophyll breakdown is the removal of central Mg by Mg-dechelatase. This reaction is the rate-limiting step in the chlorophyll breakdown pathway. We evaluated the effect of induced chlorophyll breakdown on abscission through the removal of Mg by Mg-dechelatase. Poplar transformants carrying the dexamethasone-inducible Mg-dechelatase gene were prepared using the Arabidopsis Stay-Green1 cDNA. When leaves were treated with dexamethasone, chlorophyll was degraded, photosynthetic capacity was reduced, and an abscission zone was formed, resulting in leaf abscission. In addition, ethylene, which plays an important role during senescence, was produced in this process. Thus, chlorophyll breakdown induces the phenotype in the same way as commonly observed during leaf senescence. This study suggests a physiological role of chlorophyll breakdown in the leaf abscission of deciduous trees. Furthermore, this study shows that the dexamethasone-inducible gene expression system is an available option for deciduous tree studies.

Characterization of the pheophorbide a oxygenase/phyllobilin pathway of chlorophyll breakdown in grasses.

Although the PAO/phyllobilin pathway of chlorophyll breakdown is active in grass leaf senescence, the abundance of phyllobilins is far below the amount of degraded chlorophyll. The yellowing of fully developed leaves is the most prominent visual symptom of plant senescence. Thereby, chlorophyll is degraded via the so-called pheophorbide a oxygenase (PAO)/phyllobilin pathway to a species-specific set of phyllobilins, linear tetrapyrrolic products of chlorophyll breakdown. Here, we investigated the diversity and abundance of phyllobilins in cereal and forage crops, i.e. barley, rice, ryegrass, sorghum and wheat, using liquid chromatography-mass spectrometry. A total of thirteen phyllobilins were identified, among them four novel, not yet described ones, pointing to a rather high diversity of phyllobilin-modifying activities present in the Gramineae. Along with these phyllobilins, barley orthologs of known Arabidopsis thaliana chlorophyll catabolic enzymes were demonstrated to localize in the chloroplast, and two of them, i.e. PAO and pheophytin pheophorbide hydrolase, complemented respective Arabidopsis mutants. These data confirm functionality of the PAO/phyllobilin pathway in grasses. Interestingly, when comparing phyllobilin abundance with amounts of degraded chlorophyll in senescent leaves, in most analyzed grass species only minor fractions of chlorophyll were recovered as phyllobilins, opposite to A. thaliana where phyllobilin quantities match degraded chlorophyll rather well. These data show that, despite the presence and activity of the PAO/phyllobilin pathway in barley (and other cereals), phyllobilins do not accumulate stoichiometrically, implying possible degradation of chlorophyll beyond the phyllobilin level.

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.

A dioxobilane as product of a divergent path of chlorophyll breakdown in Norway maple.

Chlorophyll breakdown is a hallmark of leaf senescence and a major contributor to the emergence of the fall colors.[1, 2] Strikingly, essential pieces of the puzzle of this biological phenomenon have been solved only within the last two decades.[2–5] A breakthrough was the identification and structure elucidation of a colorless tetrapyrrolic chlorophyll catabolite, thereafter named Hv-NCC-1.[6] The further characterization of tetrapyrrolic chlorophyll catabolites in higher plants has meanwhile provided the structural basis for detailed insight into the pathway of chlorophyll breakdown.[7, 8] Colorless tetrapyrroles, such as Hv-NCC-1, typically accumulate in senescent leaves of higher plants and they have been classified as “nonfluorescent” chlorophyll catabolites (NCCs).[7] Indeed, NCCs have been considered to be the “final” breakdown products of a largely common and well-controlled “linear” catabolic pathway in senescent leaves (see Scheme 1).[7, 9]

Stay-green protein, defective in Mendel's green cotyledon mutant, acts independent and upstream of pheophorbide a oxygenase in the chlorophyll catabolic pathway.

Type C stay-green mutants are defined as being defective in the pathway of chlorophyll breakdown, which involves pheophorbide a oxygenase (PAO), required for loss of green color. By analyzing senescence parameters, such as protein degradation, expression of senescence-associated genes and loss of photosynthetic capacity, we demonstrate that JI2775, the green cotyledon (i) pea line used by Gregor Mendel to establish the law of genetics, is a true type C stay-green mutant. STAY-GREEN (SGR) had earlier been shown to map to the I locus. The defect in JI2775 is due to both reduced expression of SGR and loss of SGR protein function. Regulation of PAO through SGR had been proposed. By determining PAO protein abundance and activity, we show that PAO is unaffected in JI2775. Furthermore we show that pheophorbide a accumulation in the mutant is independent of PAO. When silencing SGR expression in Arabidopsis pao1 mutant, both pheophorbide a accumulation and cell death phenotype, typical features of pao1, are lost. These results confirm that SGR function within the chlorophyll catabolic pathway is independent and upstream of PAO.

A Divergent Path of Chlorophyll Breakdown in the Model Plant Arabidopsis thaliana

A different kind of breakdown. The structure of At-NCC-3, a polar nonfluorescent chlorophyll catabolite (NCC) from the model plant Arabidopsis thaliana, deviates curiously from the known chlorophyll-breakdown pathway in higher plants: At-NCC-3 carries a hydroxymethyl group instead of a methyl group at C(7), a much discussed, specific structural link of the known NCCs with chlorophyll(ide) a.

Evolution of Chlorophyll Degradation: The Significance of RCC Reductase

Abstract: In angiosperms the key process of chlorophyll breakdown in senescing leaves is catalyzed by pheophorbide a oxygenase and RCC reductase which, in a metabolically channeled reaction, cleave the porphyrin macrocycle and produce a colourless primary catabolite, pFCC. RCC reductase is responsible for the reduction of the C20/C1 double bond of the intermediary catabolite, RCC. Depending on plant species, RCC reductase produces one of the two C1 stereoisomers, pFCC‐1 or pFCC‐2. Screening of a large number of taxa for the type of RCCR revealed that the isomer produced is uniform within families. It also revealed that type RCCR‐2 is predominant; RCCR‐1 seems to represent a recent derivation which in unrelated lineages has evolved independently from RCCR‐2. A third type of pFCC was produced by RCCR from basal pteridophytes and some gymnosperms; its structure is unknown. Collectively, the data suggest that the pathway of chlorophyll breakdown is very conserved in vascular plants. RCCR appears to represent a decisive addition to the catabolic pathway: it allows terrestrial plants to metabolize the porphyrin part of the chlorophyll molecule to photodynamically inactive final products that are stored in the vacuoles of senescing mesophyll cells.

Chlorophyll breakdown by chlorophyllase: isolation and functional expression of the Chlase1 gene from ethylene-treated Citrus fruit and its regulation during development.

We report on the isolation, functional expression and characterization of a cDNA encoding chlorophyllase, the enzyme catalyzing the first step in the chlorophyll breakdown pathway. The Chlase1 cDNA from Valencia Orange (Citrus sinensis cv. Valencia) was obtained by RT-PCR using degenerate primers based on the amino acid sequence of the previously purified protein. Chlase1 encodes a protein of 329 amino acids, including a sequence domain characterizing serine-lipases and a putative chloroplast-directing transit peptide. The Chlase1 gene encodes an active chlorophyllase enzyme which catalyzes the dephytylation of chlorophyll as shown by in vitro recombinant enzyme assays. Chlorophyllase expression at the transcript level in Valencia orange peel was found to be low and constitutive during natural fruit development without significant increase towards color-break and ripening. However, ethylene treatment induced an increase in chlorophyllase transcript at all stages of development. An enhanced response to ethylene treatment was observed during the months of October and November, corresponding to the time of natural color-break. The senescence-delaying regulator gibberellin-A3 (GA3) inhibited the effect of ethylene on chlorophyllase transcript accumulation. The data presented suggest that chlorophyllase may not be the regulator of chlorophyll breakdown during natural fruit ripening but is consistent with the notion that chlorophyll is gradually degraded during ripening due to a negative balance between synthesis and breakdown. According to this model, exogenous application of ethylene accelerates chlorophyll breakdown due to increased de novo synthesis of chlorophyllase. Further experimentation on the regulation and role of chlorophyllase in planta will be facilitated by the gene tools established in this work.

Chlorophyll breakdown in ripening fruits of Capsicum annuum

Colour changes from green to red taking place during ripening of Capsicum annuum fruits are due to transition from chloroplast to chromoplast in the exocarp. It was investigated whether the pathway of chlorophyll breakdown in developing chromoplasts comprises the same enzymatic steps as in the chloroplasts of senescent leaves. Chromoplast membranes contained high activities of phaeophorbide a oxygenase, a key enzyme of chlorophyll breakdown, which in senescent leaves has previously been identified to be responsible for the oxygenolytic cleavage of the porphyrin macrocycle. Properties such as specificity for Pheide a as substrate, requirement for reduced ferredoxin as well as lack of activity in the absence of stroma protein were identical to those of the enzyme from senescent leaves. The first identifiable product of Pheide a cleavage, a colourless fluorescent catabolite, was slightly less polar than the corresponding FCC produced by the oxygenase from barley or rape leaves.

Characterization of chlorophyll pigments in ripening canola seed (Brassica napus)

This study characterizes the chlorophyll pigments in ripeningBrassica napus seed. Seed samples, collected weekly as the crop ripened, were analyzed by high-performance liquid chromatography to characterize chlorophyll pigment composition. Chlorophyll A, chlorophyll B, pheophytin A and pheophytin B were the predominant pigments, while pheophorbide A, methylpheophorbide A and pyropheophytin A were minor components. No differences in pigment composition were observed between the three cultivars tested or between early and late seeding dates. There were differences in pigment composition between the two years of the study, which may result either from seed aging during storage or from environmental influences. Pigment composition was dependent on seed maturity, with physiologically mature green seeds containing both chlorophylls and pheophytins, but fully mature seeds containing only chlorophylls. Pheophytins and the minor components appeared transiently, presumably formed from the chlorophylls and subsequently degraded. The ratio of chlorophyll A/B increased during seed ripening, with fully mature canola seed having a chlorophyll A/B ratio twice that of physiologically mature green seed. The “B” derivatives degraded faster than the “A” derivatives, suggesting enzymatic reactions. The initial steps in the chlorophyll breakdown pathway in canola seed appear to be: Open image in new window