Chlorophyll b to Chlorophyll a Conversion Precedes Chlorophyll Degradation in Hordeum vulgare L.

Folly, Patrick; Engel, Norbert

doi:10.1074/jbc.274.31.21811

Cited by 57 publications

(27 citation statements)

References 23 publications

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“…The increased values of chlorophyll a/b after the CHX treatment could be due to conversion of chlorophyll b into chlorophyll a. This is in agreement with the results by Folly and Engel (1999) suggesting such conversion before chlorophyll degradation and it could indicate an early senescence of mustard cotyledons.…”

Section: Discussionsupporting

confidence: 81%

Changes in photosynthetic apparatus of mustard (Sinapis alba) cotyledons following cycloheximide and kinetin treatments

2008

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Biochemical and accompanying structural characteristics of the photosynthetic process were studied in mustard seedlings cultivated on medium with increasing concentrations of cycloheximide alone as well as in combination with various kinetin concentrations. After 7 days of cultivation the contents of total chlorophyll, carotenoids and content of Rubisco in mustard cotyledons were determined. The content of chlorophyll pigments and carotenoids decreased in dependence of cycloheximide concentration. Following antibiotic treatment the content of both Rubisco subunits markedly decreased. In addition cycloheximide caused disturbance in mesophyll organization and chloroplast ultrastructure. Kinetin applied with cycloheximide increased the amount of photosynthetic pigments as well as of Rubisco, compared to the cycloheximide alone. In the seedlings treated with cycloheximide+kinetin the structure of leaf mesophyll and chloroplast membrane system was similar to control. Our results indicate that kinetin diminished the negative effects of cycloheximide on photosynthetic pigments and Rubisco as well as on the structural traits of the cotyledons.

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Section: Discussionsupporting

confidence: 81%

Changes in photosynthetic apparatus of mustard (Sinapis alba) cotyledons following cycloheximide and kinetin treatments

2008

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“…The solvent provides the coupled proton directly or indirectly through neighboring residue(s) (50). We propose that electron donated by Fd red is transferred to FAD via the distal and proximal [4Fe-4S] clusters sequentially and finally to the 7-hydroxymethyl group on the chlorin ring (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Although the detailed mechanism of PCET is currently under investigation, its fundamental principle is the coupling of electron and proton transfer to cross the intermediate energy barrier (49). The HCAR-catalyzed hydroxymethyl reduction, in which a resonance-stabilized carbocation could exist as intermediate (10,50), employs proton-activated electron transfer, a type of PCET occurring in Fig. 3A.…”

Section: Discussionmentioning

confidence: 99%

Crystal Structure and Catalytic Mechanism of 7-Hydroxymethyl Chlorophyll a Reductase

Wang

Liu

2016

Journal of Biological Chemistry

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7-Hydroxymethyl chlorophyll a reductase (HCAR) catalyzes the second half-reaction in chlorophyll b to chlorophyll a conversion. HCAR is required for the degradation of light-harvesting complexes and is necessary for efficient photosynthesis by balancing the chlorophyll a/b ratio. Reduction of the hydroxymethyl group uses redox cofactors [4Fe-4S] cluster and FAD to transfer electrons and is difficult because of the strong carbonoxygen bond. Here, we report the crystal structure of Arabidopsis HCAR at 2.7-Å resolution and reveal that two [4Fe-4S] clusters and one FAD within a very short distance form a consecutive electron pathway to the substrate pocket. In vitro kinetic analysis confirms the ferredoxin-dependent electron transport chain, thus supporting a proton-activated electron transfer mechanism. HCAR resembles a partial reconstruction of an archaeal F 420 -reducing [NiFe] hydrogenase, which suggests a common mode of efficient proton-coupled electron transfer through conserved cofactor arrangements. Furthermore, the trimeric form of HCAR provides a biological clue of its interaction with light-harvesting complex II.The balance of chlorophyll metabolism is vital for plants to ensure an efficient photosynthesis and to support various biological processes (1). To this end, chlorophyll biosynthesis and degradation need to cooperate with the chlorophyll cycle, a process of interconversion between chlorophyll a and chlorophyll b (2-5). The chlorophyll a/b ratio is important for stabilization of the light-harvesting complexes (LHCs).2 In general, an increase of the chlorophyll b level correlates with accumulation of LHCs and thus improvement of light usage efficiency in normal condition; excessive chlorophyll b, however, could impair the energy transfer pathway by replacing chlorophyll a in LHCs (6). In the chlorophyll cycle, both the forward (from chlorophyll a to chlorophyll b) and the backward conversions use 7-hydroxymethyl chlorophyll a (HMChl) as the intermediate (see Fig. 1A). Chlorophyll a oxygenase catalyzes two sequential oxidation reactions from the 7-methyl to the 7-formyl group (7, 8); chlorophyll b reductase and HMChl reductase (HCAR) catalyze the reverse two sequential reduction reactions (9, 10). In addition, the reverse reduction reactions are essential for LHC-II turnover because chlorophyll degradation precedes degradation of the LHC-II apoprotein, and the chlorophyll catabolic process starts from chlorophyll a (11-13). Direct interaction between HCAR and LHC-II has been observed in senescing chloroplasts (14).HCAR is the last identified enzyme of the chlorophyll cycle (10). Bioinformatic studies have discovered that the HCAR homologues range from archaea to plants (15). They perform different roles, such as the Here, the crystal structure of Arabidopsis HCAR reveals the ligating cysteines of the two [4Fe-4S] clusters, residues involved in FAD binding, and a deep substrate pocket adjacent to the flavin ring. We established a quantitative in vitro assay, confirmed the reduced ferredoxin (Fd red )-...

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“…Similar course of changes in Chl a/b ratio to that observed by our group in T. baccata was also present in Piper betle L. (Kumar et al, 2006) for which it reached the highest value in November (that is a month earlier than T. baccata observed by our group), and these values were slightly higher for male in comparison to female individuals. Higher value of Chl a/b ratio in male individuals may be caused by a higher degree of conversion of Chl b into Chl a by specific enzymes (Folly & Engel, 1999;Scheumann et al, 1999) or higher membrane sensitivity (Zu et al, 2010).…”

Section: Discussionmentioning

confidence: 99%

Seasonal fluctuations of photosynthetic pigments content in Taxus baccata needles

Zarek¹

2016

Dendrobiology

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Yew is a coniferous, evergreen, dioecious species. The objective of the study was to present a comprehensive characteristic of changes occurring throughout the year in terms of the content of photosynthetic pigments and related compounds in the needles of yew, depending on the sex of individuals and age of needles. Eight compounds, particularly chlorophyll a (Chl a), chlorophyll b (Chl b), carotenoids (Car), protoporphyrin IX (PPIX), magnesium protoporphyrin IX (MgPPIX), protochlorophyllide (Pchlide), chlorophyllide a (Chlide a), and chlorophyllide b (Chlide b), were subjected to quantitative analysis. Based on the several parameters under study, significant differences between male and female individuals were observed, while most commonly, the largest differences were reported in the autumn and winter period. They were related to the content of Chl a, Chl b and Chl/Car ratio. The remaining compounds showed no significant differences according to the sex and were slightly different only in single periods. For all the studied parameters except for Chl/Car ratio, interaction between sampling dates and sex was not statistically significant. Significant differences between the needles of different age were observed only in terms of the content of Chl b, MgPPIX, Pchlide, Chlide b, and Chl a/b ratio, and these differences were always caused by the current-year needles.

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Chlorophyll b to Chlorophyll a Conversion Precedes Chlorophyll Degradation in Hordeum vulgare L.

Cited by 57 publications

References 23 publications

Changes in photosynthetic apparatus of mustard (Sinapis alba) cotyledons following cycloheximide and kinetin treatments

Changes in photosynthetic apparatus of mustard (Sinapis alba) cotyledons following cycloheximide and kinetin treatments

Crystal Structure and Catalytic Mechanism of 7-Hydroxymethyl Chlorophyll a Reductase

Seasonal fluctuations of photosynthetic pigments content in Taxus baccata needles

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