Iron tolerance and the role of aerenchyma in wetland plants

The relative iron (II) tolerance of a range of wetland plants was determined and compared with some species characteristic of well drained soils. A wide range of tolerance occurred amongst the wetland species but they were generally more tolerant than those from well drained soils. No correlation was found between iron (II) tolerance and the amount of air space {% v/v) (aerenchyma) in the roots of these species. There was a significant negative correlation between air space and iron uptake by roots. This may have been caused by iron (II) oxidation in the rhizosphere resulting in decreased availability. There was evidence that differential iron (II) tolerance of excised root tips was maintained under aerobic and anaerobic conditions. It was thus suggested that iron (II) tolerance may not be dependent on iron exclusion or oxidation of iron (II) by oxygen diffusing through the aerenchyma. Levels of malic and citric acids in roots were altered by iron (II) sulphate, but the absolute levels and changes in levels had no correlation with the iron (II) tolerance, of the species. Peroxidase and catalase activities in root tips of plants gown in drained and flooded sand culture were measured and considered in relation to the oxidising power of roots. Activity was detected in all species examined but was generally I unaffected by flooding. Evidence from the literature suggested that these enzymes of peroxide metabolism are unlikely to be active in flooded roots and so could not mediate their oxidising power. The structure of root aerenchyma had great variability between species. The Cyperaceae had the most complex and well organised structure. Growth under flooded conditions increased air space in most species, but there were exceptions. In Eriophrum angustifolium and E. vaginatum air space was high under drained conditions and was not increased by flooding. In Filipendula ulmaria the small amount of air space was not increased by flooding. Low nutrient levels increased air space production in Nardus stricta. The function of aerenchyma and the influence of environmental factors on its production are discussed

Synthetic metabolons for metabolic engineering.

Journal ArticleResearch Support, Non-U.S. Gov'tReviewThis is a pre-copyedited, author-produced PDF of an article accepted for publication in Journal of Experimental Botany following peer review. The definitive publisher-authenticated version J. Exp. Bot. (2014) 65 (8) pp. 1947-1954 is available online at: http://jxb.oxfordjournals.org/content/65/8/1947It has been proposed that enzymes can associate into complexes (metabolons) that increase the efficiency of metabolic pathways by channelling substrates between enzymes. Metabolons may increase flux by increasing the local concentration of intermediates, decreasing the concentration of enzymes needed to maintain a given flux, directing the products of a pathway to a specific subcellular location or minimizing the escape of reactive intermediates. Metabolons can be formed by relatively loose non-covalent protein-protein interaction, anchorage to membranes, and (in bacteria) by encapsulation of enzymes in protein-coated microcompartments. Evidence that non-coated metabolons are effective at channelling substrates is scarce and difficult to obtain. In plants there is strong evidence that small proportions of glycolytic enzymes are associated with the outside of mitochondria and are effective in substrate channelling. More recently, synthetic metabolons, in which enzymes are scaffolded to synthetic proteins or nucleic acids, have been expressed in microorganisms and these provide evidence that scaffolded enzymes are more effective than free enzymes for metabolic engineering. This provides experimental evidence that metabolons may have a general advantage and opens the way to improving the outcome of metabolic engineering in plants by including synthetic metabolons in the toolbox

Ascorbate deficiency influences the leaf cell wall glycoproteome in Arabidopsis thaliana

© 2014 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.The cell wall forms the first line of interaction between the plant and the external environment. Based on the observation that ascorbate-deficient vtc mutants of Arabidopsis thaliana have increased cell wall peroxidase activity, the cell wall glycoproteome of vtc2-2 was investigated. Glycoproteins were purified from fully expanded leaves by Concanavalin A affinity chromatography and analysed by liquid chromatography quadrupole time-of-flight mass spectrometry. This procedure identified 63 proteins with predicted glycosylation sites and cell wall localization. Of these, 11 proteins were differentially expressed between vtc2-2 and wild type. In particular, PRX33/34 were identified as contributing to increased peroxidase activity in response to ascorbate deficiency. This is the same peroxidase previously shown to contribute to hydrogen peroxide generation and pathogen resistance. Three fasciclin-like arabinogalactan proteins (FLA1, 2 and 8) had lower abundance in vtc2-2. Inspection of published microarray data shows that these also have lower gene expression in vtc1 and vtc2-1 and are decreased in expression by pathogen challenge and oxidative stresses. Ascorbate deficiency therefore impacts expression of cell wall proteins involved in pathogen responses and these presumably contribute to the increased resistance of vtc mutants to biotrophic pathogens.Hazara University (Mansehra, NWFP, Pakistan)Higher Education Commission (Pakistan)BBSRCExeter University Science Strategy Fun

Evolutionary temperature compensation of carbon fixation in marine phytoplankton

The efficiency of carbon sequestration by the biological pump could decline in the coming decades because respiration tends to increase more with temperature than photosynthesis. Despite these differences in the short-term temperature sensitivities of photosynthesis and respiration, it remains unknown whether the long-term impacts of global warming on metabolic rates of phytoplankton can be modulated by evolutionary adaptation. We found that respiration was consistently more temperature dependent than photosynthesis across 18 diverse marine phytoplankton, resulting in universal declines in the rate of carbon fixation with short-term increases in temperature. Long-term experimental evolution under high temperature reversed the short-term stimulation of metabolic rates, resulting in increased rates of carbon fixation. Our findings suggest that thermal adaptation may therefore have an ameliorating impact on the efficiency of phytoplankton as primary mediators of the biological carbon pump

The influence of ascorbate on anthocyanin accumulation during high light acclimation in Arabidopsis thaliana: further evidence for redox control of anthocyanin synthesis

PublishedArticleThis is the peer reviewed version of the following article: AGE, M., SULTANA, N., PASZKIEWICZ, K., FLORANCE, H. and SMIRNOFF, N. (2012), The influence of ascorbate on anthocyanin accumulation during high light acclimation in Arabidopsis thaliana: further evidence for redox control of anthocyanin synthesis. Plant, Cell & Environment, 35: 388–404. , which has been published in final form at http://dx.doi.org/10.1111/j.1365-3040.2011.02369. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Ascorbate and anthocyanins act as photoprotectants during exposure to high light (HL). They accumulate in Arabidopsis leaves in response to HL on a similar time-scale, suggesting a potential relationship between them. Flavonoids and related metabolites were identified and profiled by LC-MS/MS. The ascorbate deficient mutants vtc1, vtc2 and vtc3 accumulated less anthocyanin than wild-type during HL acclimation. In contrast, kaempferol glycoside accumulation was less affected by light and not decreased by ascorbate deficiency, while sinapoyl malate levels decreased during HL acclimation. Comparison of six Arabidopsis ecotypes showed a positive correlation between ascorbate and anthocyanin accumulation in HL. mRNA-Seq analysis showed that all flavonoid biosynthesis transcripts were increased by HL acclimation in wild-type. RT-PCR analysis showed that vtc1 and vtc2 were impaired in HL induction of transcripts of anthocyanin biosynthesis enzymes, and the transcription factors PAP1, GL3 and EGL3 that activate the pathway. Abscisic acid and jasmonic acid, hormones that could affect anthocyanin accumulation, were unaffected in vtc mutants. It is concluded that HL induction of anthocyanin synthesis involves a redox-sensitive process upstream of the known transcription factors. Because anthocyanins accumulate in preference to kaempferol glycosides and sinapoyl malate in HL, they might have specific properties that make them useful in high light acclimation.Biotechnology and Biological SciencesResearch Council (BBSRC)Exeter University ScienceStrategy FundHazara UniversityMansehra (NWFP) PakistanHigher Education Commission (Pakistan

Genetic determinants of Vitamin C content in higher plants

Ascorbic acid (AsA, VitC) is the most abundant water-soluble antioxidant in plants and it plays a plethora of biological roles including resistance to abiotic stress. Hence, including VitC as a trait to improve in breeding programs is not only a way to enhance food quality but also to increase resistance to expected environmental alterations due to global change like drought, salinity or heat. Although all components of the Smirnoff-Wheeler pathway of AsA in plants are known, little information is available about how their regulation at the biochemical and cellular levels is. We have generated a number of molecular tools such as tagged constructs, stable transgenics and mutant lines with the aim of getting detailed information about how this pathway operate in plants. We will present data on protein localization, interaction among different components and their role in affecting VitC levels using a heterologous system such as Nicotiana bethamiana. This research was supported by a grant from the Spanish Ministerio de Educación, Cultura y Deporte para la formación del Profesorado Universitario (FPU014/01974), as well as by a project funded by the Spanish Ministerio de Ciencia e Innovación (BIO2014-55380R; BIO2014-56153-REDT). We also acknowledge the support by the Plan Propio from University of Malaga, Campus de Excelencia Internacional de Andalucía.This research was supported by a grant from the Spanish Ministerio de Educación, Cultura y Deporte para la formación del Profesorado Universitario (FPU014/01974), as well as by a project funded by the Spanish Ministerio de Ciencia e Innovación (BIO2014-55380R; BIO2014-56153-REDT). We also acknowledge the support by the Plan Propio from University of Malaga, Campus de Excelencia Internacional de Andalucía

Self-incompatibility triggers irreversible oxidative modification of proteins in incompatible pollen

Self-incompatibility (SI) is used by many angiosperms to prevent self-fertilization and inbreeding. In common poppy (Papaver rhoeas), interaction of cognate pollen and pistil S-determinants triggers programmed cell death (PCD) of incompatible pollen. We previously identified that reactive oxygen species (ROS) signal to SI-PCD. ROS-induced oxidative posttranslational modifications (oxPTMs) can regulate protein structure and function. Here, we have identified and mapped oxPTMs triggered by SI in incompatible pollen. Notably, SI-induced pollen had numerous irreversible oxidative modifications, while untreated pollen had virtually none. Our data provide a valuable analysis of the protein targets of ROS in the context of SI-induction and comprise a benchmark because currently there are few reports of irreversible oxPTMs in plants. Strikingly, cytoskeletal proteins and enzymes involved in energy metabolism are a prominent target of ROS. Oxidative modifications to a phosphomimic form of a pyrophosphatase result in a reduction of its activity. Therefore, our results demonstrate irreversible oxidation of pollen proteins during SI and provide evidence that this modification can affect protein function. We suggest that this reduction in cellular activity could lead to PCD

Photosynthesis-independent production of reactive oxygen species in the rice bundle sheath during high light is mediated by NADPH oxidase.

When exposed to high light, plants produce reactive oxygen species (ROS). In Arabidopsis thaliana, local stress such as excess heat or light initiates a systemic ROS wave in phloem and xylem cells dependent on NADPH oxidase/respiratory burst oxidase homolog (RBOH) proteins. In the case of excess light, although the initial local accumulation of ROS preferentially takes place in bundle-sheath strands, little is known about how this response takes place. Using rice and the ROS probes diaminobenzidine and 2',7'-dichlorodihydrofluorescein diacetate, we found that, after exposure to high light, ROS were produced more rapidly in bundle-sheath strands than mesophyll cells. This response was not affected either by CO2 supply or photorespiration. Consistent with these findings, deep sequencing of messenger RNA (mRNA) isolated from mesophyll or bundle-sheath strands indicated balanced accumulation of transcripts encoding all major components of the photosynthetic apparatus. However, transcripts encoding several isoforms of the superoxide/H2O2-producing enzyme NADPH oxidase were more abundant in bundle-sheath strands than mesophyll cells. ROS production in bundle-sheath strands was decreased in mutant alleles of the bundle-sheath strand preferential isoform of OsRBOHA and increased when it was overexpressed. Despite the plethora of pathways able to generate ROS in response to excess light, NADPH oxidase-mediated accumulation of ROS in the rice bundle-sheath strand was detected in etiolated leaves lacking chlorophyll. We conclude that photosynthesis is not necessary for the local ROS response to high light but is in part mediated by NADPH oxidase activity

Spatial chloroplast-to-nucleus signalling involving plastid-nuclear complexes and stromules

Communication between chloroplasts and the nucleus in response to various environmental cues may be mediated by various small molecules. Signalling specificity could be enhanced if the physical contact between these organelles facilitates direct transfer and prevents interference from other subcellular sources of the same molecules. Plant cells have plastidnuclear complexes, which provide close physical contact between these organelles. plastidnuclear complexes have been proposed to facilitate transfer of photosynthesis-derived H₂O₂ to the nucleus in high light. Stromules (stroma filled tubular plastid extensions) may provide an additional conduit for transfer of a wider range of signalling molecules, including proteins. However, plastid-nuclear complexes and stromules have been hitherto treated as distinct phenomena. We suggest that plastid-nuclear complexes and stromules work in a coordinated manner so that, according to environmental conditions or developmental state the two modes of connection contribute to varying extents. We hypothesise that this association is dynamic and that there may be a link between plastid-nuclear complexes and the development of stromules. Furthermore, the changes in contact could alter signalling specificity by allowing an extended or different range of signalling molecules to be delivered to the nucleus

Making open data work for plant scientists

Despite the clear demand for open data sharing, its implementation within plant science is still limited. This is, at least in part, because open data-sharing raises several unanswered questions and challenges to current research practices. In this commentary, some of the challenges encountered by plant researchers at the bench when generating, interpreting, and attempting to disseminate their data have been highlighted. The difficulties involved in sharing sequencing, transcriptomics, proteomics, and metabolomics data are reviewed. The benefits and drawbacks of three data-sharing venues currently available to plant scientists are identified and assessed: (i) journal publication; (ii) university repositories; and (iii) community and project-specific databases. It is concluded that community and project-specific databases are the most useful to researchers interested in effective data sharing, since these databases are explicitly created to meet the researchers’ needs, support extensive curation, and embody a heightened awareness of what it takes to make data reuseable by others. Such bottom-up and community-driven approaches need to be valued by the research community, supported by publishers, and provided with long-term sustainable support by funding bodies and government. At the same time, these databases need to be linked to generic databases where possible, in order to be discoverable to the majority of researchers and thus promote effective and efficient data sharing. As we look forward to a future that embraces open access to data and publications, it is essential that data policies, data curation, data integration, data infrastructure, and data funding are linked together so as to foster data access and research productivity