Protochlorophyllide reduction - what is new in 2005?

This Current Topic focuses on light-dependent protochlorophyllide oxidoreductase (POR, EC 1.3.1.33). POR catalyzes the penultimate reaction of chlorophyll biosynthesis, i.e., the light-triggered reduction of protochlorophyllide to chlorophyllide. In this reaction, the chlorin ring of the chlorophyll molecule is formed, which is crucial for photosynthesis. POR is one of very few enzymes that are driven by light; however, it is unique in the need for its substrate to absorb photons to induce the conformational changes in the enzyme, which are required for its catalytic activation. Moreover, the enzyme is also involved in the negative feedback of the chlorophyll biosynthesis pathway and controls chlorophyll content via its light-dependent activity. Even though it has been almost 70 years since the first isolation of active POR complexes, our knowledge of them has markedly advanced in recent years. In this review, we summarize the current state of knowledge of POR, including the phylogenetic roots of POR, the mechanisms of the regulation of POR genes expression, the regulation of POR activity, the import of POR into plastids, the role of POR in PLB formation, and the molecular mechanism of protochlorophyllide reduction by POR. To the best of our knowledge, no previous review has compiled such a broad set of recent findings about POR.

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“…In vivo POR forms oligomers with a characteristic fluorescence emission of 655 nm (hereafter: F655) (measured at 77K) 90 …”

Section: Substrates Binding and Reaction Mechanismmentioning

confidence: 99%

Light-Dependent Protochlorophyllide Oxidoreductase: Phylogeny, Regulation, and Catalytic Properties

2015

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“…Pigments The inhibitory effect of excess metals on chlorophyll and carotenoid biosynthesis (reviewed by Bertrand and Poirier 2005;Schoefs 2005) and on photosynthesis (reviewed by Myśliwa-Kurdziel et al 2004;Sárvári 2005;Fodor 2006;Briat et al 2007) are reviewed elsewhere in more detail.…”

Section: Molecules Impacted By Metalsmentioning

confidence: 99%

Soil metals, chloroplasts, and secure crop production: a review

Solymosi

Bertrand²

2011

Agron. Sustain. Dev.

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with unbalanced metal concentrations are used worldwide for crop cultivation. Even though plants are able to develop strategies to cope with metal stress, either metal deficiency or excess, this unbalance affects the whole plant. Chloroplasts are key organelles for organic matter synthesis and biomass production. Under metal stress, chloroplasts suffer severe alterations of their ultrastructure, associated with profound molecular and metabolic damages. These alterations are accompanied by unbalanced metal distribution in plants, in particular in edible crop organs. Toxic metals get either accumulated or there is a deficiency of nutrients, resulting in a weak nutritional value. Nonetheless, there is more and more knowledge on the functioning and regulation of metal transporters in plants. Such knowledge will allow growing crops with well-balanced metal concentrations in edible parts even on metal unbalanced soils. This review shows that almost all vital functions of chloroplasts, such as photosynthesis, CO 2 fixation, nitrogen and sulfur assimilation, and protein and nucleic acid metabolism, require metals. Therefore, the uptake of essential metals is necessary for the proper functioning of chloroplasts and, in turn, for crop productivity. We describe nutrient uptake mechanisms of plants and processes that influence essential and non-essential metal concentrations in different plant organs. We present an overview of metal transporters in chloroplasts. Several questions still need to be elucidated about the uptake and the trafficking of essential and non-essential metals into and within chloroplasts. Similarly to transporters present in other cellular compartments, the carriers are often not metal-specific. Therefore, essential and non-essential metals may compete for carriers. As a result, unbalanced soil metal concentrations can be reflected in the plants and in the chloroplasts. Metal deficiency or excess causes reduced growth and decreased productivity of crops. It can lead to human malnutrition. Several complex physiological processes can be responsible for the reduced biomass observed in plants with unbalanced metal concentration. In this review, we have focused on the structural and functional alterations of chloroplasts under metal deficiency or excess. Interestingly, besides specific differences, our data indicate several similarities in the response of chloroplasts to metal deficiency or excess. Indeed, oxidative stress and several ultrastructural alterations, e.g., increase in the number and size of plastoglobuli, disorganized grana and disturbed thylakoids, and swelling of the intrathylakoidal space, are observed in both cases. This indicates that changes in chloroplast ion homeostasis rather than the specific effect of a metal are responsible for decreased plant productivity. Therefore, sustainable agriculture has to take into consideration solutions that enable undisturbed metal and ion homeostasis in chloroplasts of crop plants grown even in soils with unbalanced metal concentrations.Abstract An incr...

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“…LPOR is a single polypeptide enzyme classified as short-chain dehydrogenase/reductase (SDR) enzyme [76,77]. The mechanism and regulation of light-triggered Pchlide reduction has been the subject of several reviews [78][79][80]. The light-triggered Pchlide photoreduction plays a fundamental role in plant deetiolation, which is the switch between the growth in the absence (skotomorphogenesis) and in the presence (photomorphogenesis) of light (reviewed in [74,75]).…”

Section: Fig (2)mentioning

confidence: 99%

“…Pchlide reduction is not triggered in darkgerminated angiosperms, therefore Chl biosynthesis is arrested and Pchlide gets accumulated in peculiar plastids developing in the absence of light, the so-called etioplasts. The characteristic feature of the inner membranes of etioplasts is the presence of a highly regular threedimensional paracrystalline lattice that is built of tubular membranes containing ternary complexes of Pchlide:LPOR:NADPH (reviewed in [75,79,81,82]).…”

Section: Fig (2)mentioning

confidence: 99%