Regulation of nitrate reductase and phosphoenolpyruvate carboxylase activities in barley leaf protoplasts

Lillo, Cathrine; Smith, Lucy H.; Nimmo, Hugh G.; Wilkins, Malcolm B.

doi:10.1007/bf00208307

Cited by 24 publications

(12 citation statements)

References 32 publications

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“…Much less is known about PP2As in plants (Terol et al 2002;Farkas et al 2007; Wang et al 2007). In higher plants, the cytosolic enzymes nitrate reductase and sucrose-phosphate synthase, are dephosphorylated by a PP2A in vitro, and most likely also in vivo according to evidence from inhibitory studies (Siegl et al 1990;Lillo et al 1996;MacKintosh 1998;Lillo 2008). PP2A has also been speciWcally shown to be involved in microtubule organization, regulation of PIN auxin transport proteins, and root morphogenesis (Camilleri et al 2002;Michniewicz et al 2007;Blakeslee et al 2008).…”

Section: Introductionmentioning

confidence: 96%

Diversity in subcellular targeting of the PP2A B′η subfamily members

Matre

Meyer

Lillo

2009

Planta

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Protein phosphatase 2A (PP2A) is a serine/threonine-specific phosphatase comprising a catalytic subunit (C), a scaffolding subunit (A), and a regulatory subunit (B). The B subunits are believed to be responsible for substrate specificity and localization of the PP2A complex. In plants, three families of B subunits exist, i.e. B (B55), B', and B''. Here, we report differential subcellular targeting within the Arabidopsis B'eta subfamily, which consists of the close homologs B'eta, B'theta, B'gamma and B'zeta. Phenotypes of corresponding knockouts were observed, and particularly revealed delayed flowering for the B'eta knockout. The B' subunits were linked to fluorescent tags and transiently expressed in various tissues of onion, tobacco and Arabidopsis. B'eta and B'gamma targeted the cytosol and nucleus. B'zeta localized to the cytoplasm and partly co-localized with mitochondrial markers when the N-terminus was free. Provided its C-terminus was free, the B'theta subunit targeted peroxisomes. The importance of the C-terminal end for peroxisomal targeting was further confirmed by truncation of the C-terminus. The results revealed that the closely related B' subunits are targeting different organelles in plants, and exemplify the usage of the peptide serine-serine-leucine as a PTS1 peroxisomal signaling peptide.

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Section: Introductionmentioning

confidence: 96%

Diversity in subcellular targeting of the PP2A B′η subfamily members

Matre

Meyer

Lillo

2009

Planta

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“…Microcystin-LR and okadaic acid, which are known inhibitors of the protein phosphatase families protein phosphatase 1 (PP1), PP2A, PP4, PP5, PP6, and PPPKelch, prevented light activation of NR in spinach (Spinacia oleracea) leaves and barley (Hordeum vulgare) protoplasts (MacKintosh, 1992;Lillo et al, 1996). Okadaic acid and microcystin also prevented activation of NR in extracts of leaves, whereas inhibitor 2 (known inhibitor of the PP1 family) had no effect.…”

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confidence: 99%

Protein Phosphatase 2A B55 and A Regulatory Subunits Interact with Nitrate Reductase and Are Essential for Nitrate Reductase Activation

et al. 2011

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Posttranslational activation of nitrate reductase (NR) in Arabidopsis (Arabidopsis thaliana) and other higher plants is mediated by dephosphorylation at a specific Ser residue in the hinge between the molybdenum cofactor and heme-binding domains. The activation of NR in green leaves takes place after dark/light shifts, and is dependent on photosynthesis. Previous studies using various inhibitors pointed to protein phosphatases sensitive to okadaic acid, including protein phosphatase 2A (PP2A), as candidates for activation of NR. PP2As are heterotrimeric enzymes consisting of a catalytic (C), structural (A), and regulatory (B) subunit. In Arabidopsis there are five, three, and 18 of these subunits, respectively. By using inducible artificial microRNA to simultaneously knock down the three structural subunits we show that PP2A is necessary for NR activation. The structural subunits revealed overlapping functions in the activation process of NR. Bimolecular fluorescence complementation was used to identify PP2A regulatory subunits interacting with NR, and the two B55 subunits were positive. Interactions of NR and B55 were further confirmed by the yeast two-hybrid assay. In Arabidopsis the B55 group consists of the close homologs B55a and B55b. Interestingly, the homozygous double mutant (b55a 3 b55b) appeared to be lethal, which shows that the B55 group has essential functions that cannot be replaced by other regulatory subunits. Mutants homozygous for mutation in Bb and heterozygous for mutation in Ba revealed a slower activation rate for NR than wild-type plants, pointing to these subunits as part of a PP2A complex responsible for NR dephosphorylation.Nitrate reductase (NR), a key enzyme in nitrogen assimilation, reduces nitrate to nitrite in the cytosol. The nitrite formed is further reduced to ammonium in the plastids, whereafter ammonium is incorporated into amino acids. Regulation of NR takes place at the transcriptional as well as posttranslational level. At both levels signals from the chloroplasts are involved in initiating an increase in NR activity levels, but these signals and their processing are still unknown (Jonassen et al.,

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“…In addition, sustained algae photosynthetic activity coupled with nitrification and nitrate consumption leads to an increase in medium pH. Most of the energy for nitrate assimilation arises from photosynthesis, photosynthesis is also reported to be responsible for light regulation of nitrate reductase gene expression and activity (Lillo et al, 1996;Oswald et al, 2001), and linear electron flow and generation of reducing equivalents are promoted by photosystem 1 (PS l) light absorption which is believed to facilitate reduction of assimilated nitrate alongside CO 2 (Sherameti et al, 2002). Thus, as long as nitrate is abstracted, reduced to ammonium and the ammonium assimilated into amino nitrogen, a 1:1 alkalinisation in relation to nitrate consumption is maintained (Ullrich and Novacky, 1990;Mistrik and Ullrich, 1996;Ullrich et al, 1998).…”

Section: Iaps Design and Operationmentioning

confidence: 99%

The Belmont Valley integrated algae pond system in retrospect

Mambo¹,

Westensee²,

Zuma³

et al. 2014

WSA

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Integrated Algae Pond Systems (IAPS) are a derivation of the Oswald-designed Algal Integrated Wastewater Pond Systems (AIWPS®) and combine the use of anaerobic and aerobic bioprocesses to effect sewage treatment. IAPS technology was introduced to South Africa in 1996 and a pilot plant designed and commissioned at the Belmont Valley WWTW in Grahamstown. The system has been in continual use since implementation, and affords secondarily treated water for reclamation according to its design specifications, which most closely resemble those of the AIWPS Advanced Secondary Process. In this paper IAPS as a municipal sewage treatment technology is re-examined in relation to design and operation, the underpinning biochemistry of nutrient removal by algae is described, and a retrospective is provided on the demonstration system at the Belmont Valley WWTW. In addition to presenting details of the process flow, several shortcomings and/or oversights are highlighted and, in particular, the need for an appropriate tertiary treatment component. However, despite the use of IAPS for sewage treatment in many countries, this technology is still viewed with some scepticism. Thus, a major purpose of this overview is to provide a synthesis of available information on IAPS and an appraisal of its use for municipal sewage treatment.

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Regulation of nitrate reductase and phosphoenolpyruvate carboxylase activities in barley leaf protoplasts

Cited by 24 publications

References 32 publications

Diversity in subcellular targeting of the PP2A B′η subfamily members

Diversity in subcellular targeting of the PP2A B′η subfamily members

Protein Phosphatase 2A B55 and A Regulatory Subunits Interact with Nitrate Reductase and Are Essential for Nitrate Reductase Activation

The Belmont Valley integrated algae pond system in retrospect

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