| 1. |
- Adolfsson, Lisa, 1984, et al.
(författare)
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Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula.
- 2017
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Ingår i: Plant physiology. - : Oxford University Press (OUP). - 1532-2548 .- 0032-0889. ; 175:1, s. 392-411
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Tidskriftsartikel (refereegranskat)abstract
- Arbuscular mycorrhizas (AM) are the most common symbiotic associations between a plant's root compartment and fungi. They provide nutritional benefit (mostly inorganic phosphate [Pi]), leading to improved growth, and nonnutritional benefits, including defense responses to environmental cues throughout the host plant, which, in return, delivers carbohydrates to the symbiont. However, how transcriptional and metabolic changes occurring in leaves of AM plants differ from those induced by Pi fertilization is poorly understood. We investigated systemic changes in the leaves of mycorrhized Medicago truncatula in conditions with no improved Pi status and compared them with those induced by high-Pi treatment in nonmycorrhized plants. Microarray-based genome-wide profiling indicated up-regulation by mycorrhization of genes involved in flavonoid, terpenoid, jasmonic acid (JA), and abscisic acid (ABA) biosynthesis as well as enhanced expression of MYC2, the master regulator of JA-dependent responses. Accordingly, total anthocyanins and flavonoids increased, and most flavonoid species were enriched in AM leaves. Both the AM and Pi treatments corepressed iron homeostasis genes, resulting in lower levels of available iron in leaves. In addition, higher levels of cytokinins were found in leaves of AM- and Pi-treated plants, whereas the level of ABA was increased specifically in AM leaves. Foliar treatment of nonmycorrhized plants with either ABA or JA induced the up-regulation of MYC2, but only JA also induced the up-regulation of flavonoid and terpenoid biosynthetic genes. Based on these results, we propose that mycorrhization and Pi fertilization share cytokinin-mediated improved shoot growth, whereas enhanced ABA biosynthesis and JA-regulated flavonoid and terpenoid biosynthesis in leaves are specific to mycorrhization.
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| 2. |
- Beebo, Azeez, 1979, et al.
(författare)
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Assessment of the requirement for aquaporins in the thylakoid membrane of plant chloroplasts to sustain photosynthetic water oxidation
- 2013
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Ingår i: Febs Letters. - : Wiley. - 0014-5793. ; 587:14, s. 2083-2089
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Tidskriftsartikel (refereegranskat)abstract
- Oxygenic photosynthetic organisms use sunlight energy to oxidize water to molecular oxygen. This process is mediated by the photosystem II complex at the lumenal side of the thylakoid membrane. Most research efforts have been dedicated to understanding the mechanism behind the unique water oxidation reactions, whereas the delivery pathways for water molecules into the thylakoid lumen have not yet been studied. The most common mechanisms for water transport are simple diffusion and diffusion facilitated by specialized channel proteins named aquaporins. Calculations using published data for plant chloroplasts indicate that aquaporins are not necessary to sustain water supply into the thylakoid lumen at steady state photosynthetic rates. Yet, arguments for their presence in the plant thylakoid membrane and beneficial action are presented.
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| 3. |
- Beebo, Azeez, 1979, et al.
(författare)
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Photosynthetic Water Oxidation Requires Water Transport Across the Thylakoid Membrane: Are Aquaporins Involved?
- 2012
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Ingår i: Current Chemical Biology. - : Bentham Science Publishers Ltd.. - 1872-3136 .- 2212-7968. ; 6:3, s. 244-253
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Tidskriftsartikel (refereegranskat)abstract
- Water supply is crucial for the development and growth of all living organisms. This is especially true for oxygenic photosynthetic organisms (cyanobacteria, algae and terrestrial plants), which use water as a substrate to produce molecular oxygen through the activity of the water-oxidizing photosystem II complex. The precise site of water oxidation is on the lumenal side of the thylakoid membrane, harboring this complex. How water molecules reach the thylakoid lumen to sustain oxygen production is a crucial question. To date, the mechanism of water transport across the thylakoid membrane is unknown. Within the cell, the most common mechanisms for water transport are free diffusion and facilitated diffusion, the latter being mediated by specialized channel proteins named aquaporins. In this review, the following questions are addressed: 1) Could free diffusion through the thylakoid membrane provide sufficient amounts of water for effective photosynthetic reaction? or 2) Are aquaporins involved in water transport across the thylakoid membrane? Biophysical studies and theoretical calculations support the second possibility. Moreover, several aquaporins have been found using mass spectrometry-based proteomics in plant chloroplast membranes. Validation of their chloroplast location and investigation of a potential role in photosynthesis should be the focus of future studies.
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| 4. |
- Bolte, Susanne, et al.
(författare)
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Distinct Lytic Vacuolar Compartments are Embedded Inside the Protein Storage Vacuole of Dry and Germinating Arabidopsis thaliana Seeds
- 2011
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Ingår i: PLANT AND CELL PHYSIOLOGY. - 0032-0781. ; 52:7, s. 1142-1152
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Tidskriftsartikel (refereegranskat)abstract
- Plant cell vacuoles are diverse and dynamic structures. In particular, during seed germination, the protein storage vacuoles are rapidly replaced by a central lytic vacuole enabling rapid elongation of embryo cells. In this study, we investigate the dynamic remodeling of vacuolar compartments during Arabidopsis seed germination using immunocytochemistry with antibodies against tonoplast intrinsic protein (TIP) isoforms as well as proteins involved in nutrient mobilization and vacuolar acidification. Our results confirm the existence of a lytic compartment embedded in the protein storage vacuole of dry seeds, decorated by gamma-TIP, the vacuolar proton pumping pyrophosphatase (V-PPase) and the metal transporter NRAMP4. They further indicate that this compartment disappears after stratification. It is then replaced by a newly formed lytic compartment, labeled by gamma-TIP and V-PPase but not AtNRAMP4, which occupies a larger volume as germination progresses. Altogether, our results indicate the successive occurrence of two different lytic compartments in the protein storage vacuoles of germinating Arabidopsis cells. We propose that the first one corresponds to globoids specialized in mineral storage and the second one is at the origin of the central lytic vacuole in these cells.
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| 5. |
- Karlsson, Patrik Milton, et al.
(författare)
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The Arabidopsis thylakoid transporter PHT4;1 influences phosphate availability for ATP synthesis and plant growth
- 2015
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Ingår i: The Plant Journal. - : Wiley. - 0960-7412 .- 1365-313X. ; 84:1, s. 99-110
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Tidskriftsartikel (refereegranskat)abstract
- The Arabidopsis phosphate transporter PHT4;1 was previously localized to the chloroplast thylakoid membrane. Here we investigated the physiological consequences of the absence of PHT4;1 for photosynthesis and plant growth. In standard growth conditions, two independent Arabidopsis knockout mutant lines displayed significantly reduced leaf size and biomass but normal phosphorus content. When mutants were grown in high-phosphate conditions, the leaf phosphorus levels increased and the growth phenotype was suppressed. Photosynthetic measurements indicated that in the absence of PHT4;1 stromal phosphate was reduced to levels that limited ATP synthase activity. This resulted in reduced CO2 fixation and accumulation of soluble sugars, limiting plant growth. The mutants also displayed faster induction of non-photochemical quenching than the wild type, in line with the increased contribution of ΔpH to the proton-motive force across thylakoids. Small-angle neutron scattering showed a smaller lamellar repeat distance, whereas circular dichroism spectroscopy indicated a perturbed long-range order of photosystem II (PSII) complexes in the mutant thylakoids. The absence of PHT4;1 did not alter the PSII repair cycle, as indicated by wild-type levels of phosphorylation of PSII proteins, inactivation and D1 protein degradation. Interestingly, the expression of genes for several thylakoid proteins was downregulated in the mutants, but the relative levels of the corresponding proteins were either not affected or could not be discerned. Based on these data, we propose that PHT4;1 plays an important role in chloroplast phosphate compartmentation and ATP synthesis, which affect plant growth. It also maintains the ionic environment of thylakoids, which affects the macro-organization of complexes and induction of photoprotective mechanisms.
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