scholarly journals Characterization of cooperative bicarbonate uptake into chloroplast stroma in the green alga Chlamydomonas reinhardtii

2015 ◽  
Vol 112 (23) ◽  
pp. 7315-7320 ◽  
Author(s):  
Takashi Yamano ◽  
Emi Sato ◽  
Hiro Iguchi ◽  
Yuri Fukuda ◽  
Hideya Fukuzawa

The supply of inorganic carbon (Ci; CO2 and HCO3–) is an environmental rate-limiting factor in aquatic photosynthetic organisms. To overcome the difficulty in acquiring Ci in limiting-CO2 conditions, an active Ci uptake system called the CO2-concentrating mechanism (CCM) is induced to increase CO2 concentrations in the chloroplast stroma. An ATP-binding cassette transporter, HLA3, and a formate/nitrite transporter homolog, LCIA, are reported to be associated with HCO3– uptake [Wang and Spalding (2014) Plant Physiol 166(4):2040–2050]. However, direct evidence of the route of HCO3– uptake from the outside of cells to the chloroplast stroma remains elusive owing to a lack of information on HLA3 localization and comparative analyses of the contribution of HLA3 and LCIA to the CCM. In this study, we revealed that HLA3 and LCIA are localized to the plasma membrane and chloroplast envelope, respectively. Insertion mutants of HLA3 and/or LCIA showed decreased Ci affinities/accumulation, especially in alkaline conditions where HCO3– is the predominant form of Ci. HLA3 and LCIA formed protein complexes independently, and the absence of LCIA decreased HLA3 mRNA accumulation, suggesting the presence of unidentified retrograde signals from the chloroplast to the nucleus to maintain HLA3 mRNA expression. Furthermore, although single overexpression of HLA3 or LCIA in high CO2 conditions did not affect Ci affinity, simultaneous overexpression of HLA3 with LCIA significantly increased Ci affinity/accumulation. These results highlight the HLA3/LCIA-driven cooperative uptake of HCO3– and a key role of LCIA in the maintenance of HLA3 stability as well as Ci affinity/accumulation in the CCM.

1981 ◽  
Vol 49 (1) ◽  
pp. 401-409
Author(s):  
A.W. Coleman ◽  
P. Heywood

The arrangement and ultrastructure of chloroplasts is described for the Chloromonadophycean algae gonyostomum semen Diesing and Vacuolaria virescens Cienkowsky. The chloroplasts are present in large numbers and are discoid structures approximately 3–4 micrometer in length by 2–3 micrometer in width. In Gonyostomum semen the chloroplasts form a single layer immediately interior to the cell membrane; frequently their longitudinal axis parallels the longitudinal axis of the cell. The chloroplasts in Vacuolaria virescens are more than I layer deep and do not appear to be preferentially oriented. In both organisms, chloroplast bands usually consist of 3 apposed thylakoids, although fusion and interconnections between adjacent bands frequently occur. External to the girdle band (the outermost thylakoids) is the chloroplast envelope. This is bounded by endoplasmic reticulum but there is no immediately apparent continuity between this endoplasmic reticulum and the nuclear envelope. Electron-dense spheres in the chloroplast stroma are thought to be lipid food reserve. Ring-shaped electron-translucent regions in the chloroplast contain chloroplast DNA. The DNA is distributed along this ring in an uneven fashion and, when stained, resembles a string of beads. Each plastid has I ring, and the ring is unbroken in the intact plastid.


2022 ◽  
Author(s):  
Xin Liu ◽  
Wojciech J Nawrocki ◽  
Roberta Croce

Non-photochemical quenching (NPQ) is the process that protects photosynthetic organisms from photodamage by dissipating the energy absorbed in excess as heat. In the model green alga Chlamydomonas reinhardtii, NPQ was abolished in the knock-out mutants of the pigment-protein complexes LHCSR3 and LHCBM1. However, while LHCSR3 was shown to be a pH sensor and switching to a quenched conformation at low pH, the role of LHCBM1 in NPQ has not been elucidated yet. In this work, we combine biochemical and physiological measurements to study short-term high light acclimation of npq5, the mutant lacking LHCBM1. We show that while in low light in the absence of this complex, the antenna size of PSII is smaller than in its presence, this effect is marginal in high light, implying that a reduction of the antenna is not responsible for the low NPQ. We also show that the mutant expresses LHCSR3 at the WT level in high light, indicating that the absence of this complex is also not the reason. Finally, NPQ remains low in the mutant even when the pH is artificially lowered to values that can switch LHCSR3 to the quenched conformation. It is concluded that both LHCSR3 and LHCBM1 need to be present for the induction of NPQ and that LHCBM1 is the interacting partner of LHCSR3. This interaction can either enhance the quenching capacity of LHCSR3 or connect this complex with the PSII supercomplex.


2014 ◽  
Vol 4 (2) ◽  
pp. 1 ◽  
Author(s):  
Tiberio C. Monterrubio-Rico ◽  
Juan Felipe Charre Medellín ◽  
Cristina Z. Colín-Soto ◽  
Livia León Paniagua

 RESUMEN Los mamíferos silvestres han sido estudiados en Michoacán desde el siglo XVIII por renombrados zoólogos y naturalistas. Sin embargo, todavía en 1949 se reconocía solo 85 especies, y hasta el año 2005 se proporcionó estimaciones completas basadas en integración de registros disponibles tanto nacionales como de colecciones científicas internacionales, ya que la información disponible para el estado se encontraba dispersa. Como resultado de proyectos recientes con nuevos registros, el objetivo de este análisis es proporcionar una cifra actualizada sobre la riqueza taxonómica de los mamíferos silvestres terrestres en el estado de Michoacán. Existen registros de 161 especies en 9 Ordenes, 25 familias, y 94 géneros que representan el 32% de las especies de México. El Orden con mayor número de especies es Chiroptera con 74 especies que representan el 53% de las especies del Orden en México. A pesar de la ubicación central de Michoacán en el país, y ser un estado muestreado por numerosos investigadores, todavía existe carencia de información para regiones remotas, y en algunos grupos de mamíferos. Por ejemplo, el jaguar, que a pesar de ser el mayor felino del país, se carecía de confirmación para el estado, afortunadamente durante 2010 se localizó una población en el estado. Otro aspecto limitante para la interpretación adecuada de la estimación actual, es la antigüedad de muchos registros, ya que los estudios más completos realizados a escala regional, como en la costa Michoacana son de hace 30 años, y durante ese periodo se ha incrementado la deforestación de selvas tropicales, por lo que desconocemos la situación actual que presentan las poblaciones de mamíferos en el estado. En Michoacán encuentran su límite más norteño en el Pacífico tres especies de amplia distribución en el Neotrópico, Tamandua mexicana,  Potos flavus y Sphiggurus mexicanus, por lo que deben limitarse áreas que protejan sus poblaciones. Palabras clave: Distribución, Mochoacán, mamíferos, especies.ABSTRACT The wild mammals in Michoacan state have been studied since the XVIII century by reknown zoologists and naturalists. However, still in 1949 only 85 mammals species were recognized, and until 2005 a complete estimate based on the integration of national and international data bases records available from Scientific collections, since all available information was scattered. As a result of recent surveys with new records, the aim of this analysis was to provide an updated statistic of the terrestrial wild mammals taxonomic richness in the Michoacan state. Available records correspond to 161 species in 9 Orders, 25 families and 94 genera which represent 32% of the Mexican mammal species. The Order with the major number of species is Chiroptera that includes 74 species thet represent 53% of the Order in Mexico. Despite its central location in the country, and considering that the state has been surveyed by several prestigious academics, there is still a lack of information for remote regions, and for some mammal groups. For example, the jaguar, even though constitute the largest wild felid in the country, no information was available for the state, fortunately during 2010 a population was localized in the state. Another limiting factor for the adequate interpretation of the current estimate is that many records are outdated, since the most complete studies performed at a regional scale, like in the Michoaca coast, are 30 years old, and during that time-frame, tropical forest loss increased dramatically, for instance, the current situation that present the mammal populations in the state are unknown. In Michoacan three species with a broad neotropical distribution present its northernmost limit on the Pacific, Tamandua mexicana, Potos flavus, and Sphiggurus mexicanus and there is the need to establish protected areas oriented to protect their populations. Key words: Distribution, Michoacan, mammals, species.


1999 ◽  
Vol 5 (S2) ◽  
pp. 1050-1051
Author(s):  
J. Clark Lagarias ◽  
Beronda L. Montgomery ◽  
John T. Murphy ◽  
Shu-Hsing Wu

Plants sense the light environment using pigment-protein complexes that discriminate light color, intensity, duration and direction. The most well-studied of these photoreceptors are the phytochromes, a family of soluble biliproteins found in plants, algae and cyanobacteria. Owing to the linear tetrapyrrole pigment phytochromobilin (PΦB) or phycocyanobilin (PCB) that is covalently linked to a large polypeptide via a thioether linkage, phytochromes perceive differences in the quality and quantity of light via their ability to photointerconvert between red (λmax660 nm) and far-red (λmax730 nm) light absorbing forms. Due to an efficient Z,E photoisomerization of the double bond between the C and D-ring pyrroles, phytochromes are nonfluorescent proteins with fluorescent quantum yields less than 10“3 at room temperature (Figure 1).Phytochrome genes have been cloned from a wide variety of photosynthetic organisms.


1994 ◽  
Vol 266 (1) ◽  
pp. C157-C164 ◽  
Author(s):  
P. Burgener-Kairuz ◽  
I. Corthesy-Theulaz ◽  
A. M. Merillat ◽  
P. Good ◽  
K. Geering ◽  
...  

In fully grown Xenopus oocytes, the synthesis of beta-subunits is limiting for the formation of functional Na(+)-K(+)-adenosinetriphosphatase alpha/beta-complexes (Geering, K. FEBS Lett. 285: 189-193, 1991). In the present study, we show that during oocyte growth (from stage I to stage VI) alpha 1-, but not beta 1- or beta 3-isoform, mRNAs accumulate. In addition, beta-mRNAs are apparently sequestered in an untranslated pool in fully grown oocytes (stage VI). From fertilization to morulation, the total pools of alpha 1-, beta 1-, or beta 3-mRNAs vary little. Whereas polyadenylated [poly(A)+] alpha 1- and beta 3-isoform mRNAs did not change significantly, poly(A)+ beta 1-mRNA abundance increased three- to fourfold at morulation, accompanied by a parallel increase in beta 1-protein synthesis. After midblastula transition (i.e., at early gastrula) and during neurulation, poly(A)+ alpha 1- and beta 3-mRNAs accumulated rapidly, whereas poly(A)+ beta 1-mRNA accumulation was delayed by approximately 2 h, beginning only at early neurula. Our results indicate that 1) the abundance of poly(A)+ beta 1-mRNA is rate limiting during embryonic development for the assembly of alpha 1/beta 1-heterodimers, shown to be involved in the vectorial transport of sodium in kidney cells, and 2) the polyadenylation of beta 1-mRNA is a rate-limiting factor during morulation for the synthesis and assembly of new sodium pumps at the time of blastocoel fluid formation. The 3'-untranslated region of beta 1-mRNA (but not of alpha 1-mRNA) expresses cytoplasmic polyadenylation elements (CPEs) with the consensus sequence AXX-AUUUU(A/U)(A/U)(A/U). A role of CPE in the differential polyadenylation of alpha 1- and beta 1-mRNA is proposed.


2005 ◽  
Vol 83 (7) ◽  
pp. 780-795 ◽  
Author(s):  
Mautusi Mitra ◽  
Catherine B Mason ◽  
Ying Xiao ◽  
Ruby A Ynalvez ◽  
Scott M Lato ◽  
...  

Carbonic anhydrases (CAs) are zinc-containing metalloenzymes that catalyze the reversible interconversion of CO2 and HCO3–. Aquatic photosynthetic organisms have evolved different forms of CO2-concentrating mechanisms to aid Rubisco in capturing CO2 from the surrounding environment. One aspect of all CO2-concentrating mechanisms is the critical roles played by various specially localized extracellular and intracellular CAs. There are three evolutionarily unrelated CA families designated α-, β-, and γ-CA. In the green alga, Chlamydomonas reinhardtii Dangeard, eight CAs have now been identified, including three α-CAs and five β-CAs. In addition, C. reinhardtii has another CA-like gene, Glp1 that is similar to known γ-CAs. To characterize these different CA isoforms, some of the CA genes have been overexpressed to determine whether the proteins have CA activity and to generate antibodies for in vivo immunolocalization. The CA proteins Cah3, Cah6, and Cah8, and the γ-CA-like protein, Glp1, have been overexpressed. Cah3, Cah6, and Cah8 have CA activity, but Glp1 does not. At least two of these proteins, Cah3 and Cah6, are localized to the chloroplast. Using immunolocalization and sequence analyses, we have determined that Cah6 is located to the chloroplast stroma and confirmed that Cah3 is localized to the chloroplast thylakoid lumen. Activity assays show that Cah3 is 100 times more sensitive to sulfonamides than Cah6. We present a model on how these two chloroplast CAs might participate in the CO2-concentrating mechanism of C. reinhardtii. Key words: carbonic anhydrase, CO2-concentrating mechanism, Chlamydomonas, immunolocalization.


2012 ◽  
Vol 367 (1608) ◽  
pp. 3420-3429 ◽  
Author(s):  
Wei Chi ◽  
Jinfang Ma ◽  
Lixin Zhang

Major multi-protein photosynthetic complexes, located in thylakoid membranes, are responsible for the capture of light and its conversion into chemical energy in oxygenic photosynthetic organisms. Although the structures and functions of these photosynthetic complexes have been explored, the molecular mechanisms underlying their assembly remain elusive. In this review, we summarize current knowledge of the regulatory components involved in the assembly of thylakoid membrane protein complexes in photosynthetic organisms. Many of the known regulatory factors are conserved between prokaryotes and eukaryotes, whereas others appear to be newly evolved or to have expanded predominantly in eukaryotes. Their specific features and fundamental differences in cyanobacteria, green algae and land plants are discussed.


2018 ◽  
Vol 62 (1) ◽  
pp. 65-75 ◽  
Author(s):  
Serena Schwenkert ◽  
Sophie Dittmer ◽  
Jürgen Soll

Import of preproteins into chloroplasts is an essential process, requiring two major multisubunit protein complexes that are embedded in the outer and inner chloroplast envelope membrane. Both the translocon of the outer chloroplast membrane (Toc), as well as the translocon of the inner chloroplast membrane (Tic) have been studied intensively with respect to their individual subunit compositions, functions and regulations. Recent advances in crystallography have increased our understanding of the operation of these proteins in terms of their interactions and regulation by conformational switching. Several subdomains of components of the Toc translocon have been studied at the structural level, among them the polypeptide transport-associated (POTRA) domain of the channel protein Toc75 and the GTPase domain of Toc34. In this review, we summarize and discuss the insight that has been gained from these structural analyses. In addition, we present the crystal structure of the Toc64 tetratrico-peptide repeat (TPR) domain in complex with the C-terminal domains of the heat-shock proteins (Hsp) Hsp90 and Hsp70.


2021 ◽  
Author(s):  
Petra Redekop ◽  
Emanuel Sanz-Luque ◽  
Yizhong Yuan ◽  
Gaelle Villain ◽  
Dimitris Petroutsos ◽  
...  

In nature, photosynthetic organisms are exposed to different light spectra and intensities depending on the time of day and atmospheric and environmental conditions. When photosynthetic cells absorb excess light, they induce non-photochemical quenching to avoid photo-damage and trigger expression of photoprotective genes. In this work, we used the green alga Chlamydomonas reinhardtii to assess the impact of light intensity, light quality, wavelength, photosynthetic electron transport and CO2 on induction of the photoprotective genes (LHCSR1, LHCSR3 and PSBS) during dark-to-light transitions. Induction (mRNA accumulation) occurred at very low light intensity, was independently modulated by blue and UV-B radiation through specific photoreceptors, and only LHCSR3 was strongly controlled by CO2 levels through a putative enhancer function of CIA5, a transcription factor that controls genes of the carbon concentrating mechanism. We propose a model that integrates inputs of independent signaling pathways and how they may help the cells anticipate diel conditions and survive in a dynamic light environment.


2020 ◽  
Vol 38 ◽  
Author(s):  
A. SIAHMARGUEE ◽  
M. GORGANI ◽  
F. GHADERI-FAR ◽  
R. ASGARPOUR

ABSTRACT: Ivy-leaved morning-glory (Ipomoea hederacea Jacq.) is an exotic species that is becoming an increasing problem in soybean fields of Golestan province, Iran. Because little information is available on the biology of this weed species in Iran, experiments were conducted to investigate the effects of different factors on seed germination and emergence of Ivy-leaved morning-glory. Maximum germination occurred at constant temperature of 20 oC (82%) and alternating temperature of 15/25 oC (94%). Germination was reduced with increasing salinity and drought stresses. Sodium chloride concentration and osmotic potential that inhibited 50% maximum germination were -1.64 and -1.03 MPa, respectively. Acidity was a limiting factor for the germination, due to inhibiting effect of alkaline conditions on germination. However, the results showed that high temperature pretreatment >100 oC decreased seed germination. Germination decreased from 82 to 3% as temperature increased from 100 to 130 oC. There was no significant difference between seedling emergence in burial depths of 1 to 10 cm, but emergence reduced with increasing burial depth from 10 to 14 cm, and no seedling was emerged from a depth of 15 cm. The results of the flooding experiment also revealed that the seeds of this species are sensitive to this stress, so that emergence was 9% after 3 d flooding.


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