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BSc, PhD (Wales)
Department of Biological and Medical Sciences
Faculty of Health and Life Sciences
+44 (0)1865 483968
I lead on research and knowledge exchange across a wide-ranging Faculty including healthcare, biological and biomedical science, sports science, nutrition and environment. I also undertake research in plant cell biology and have
developed an international reputation in plant nuclear envelope biology, where I co-lead the International Plant Nucleus consortium of scientists in the UK, France, Germany, Belgium, Spain, the Czech Republic, the USA, Japan and New Zealand (https://doi.org/10.24384/IPNC). Our research group is a member of the Indepth COST Action (
Aluminium (Al) and silicon (Si) are abundant in soils, but their availability for plant uptake is limited by low solubility. However, Al toxicity is a major problem in naturally occurring acid soils and in soils affected by acidic precipitation. When, in 1995, we reviewed this topic for the Journal of Experimental Botany, it was clear that under certain circumstances soluble Si could ameliorate the toxic effects of Al, an effect mirrored in organisms beyond the plant kingdom. In the 25 years since our review, it has become evident that the amelioration phenomenon occurs in the root apoplast, with the formation of hydroxyaluminosilicates being part of the mechanism. A much better knowledge of the molecular basis for Si and Al uptake by plants and of Al toxicity mechanisms has been developed. However, relating this work to amelioration by Si is at an early stage. It is now clear that co-deposition of Al and Si in phytoliths is a fairly common phenomenon in the plant kingdom, and this may be important in detoxification of Al. Relatively little work on Al/Si interactions in field situations has happened in the last 25 years, and this is a key area for future development
Protein targeting to the inner nuclear membrane (INM) is one of the least understood protein targeting pathways. INM proteins are important for chromatin organization, nuclear morphology and movement, meiosis, and have been implicated in human diseases. In opisthokonts, one mechanism is transport-factor mediated trafficking, in which nuclear localization signals (NLSs) function in nuclear import of transmembrane proteins. To explore if this pathway exists in plants, we fused the SV40 NLS to a plant ER tail-anchored protein and showed that the GFP-tagged fusion protein was significantly enriched at the NE of leaf epidermal cells. Airyscan sub-diffraction limited confocal microscopy showed that it displays localization consistent with an INM protein. Nine different monopartite and bipartite NLSs from plants and opisthokonts, fused to a chimeric tail-anchored membrane protein, were all sufficient for NE enrichment and both monopartite or bipartite NLSs were sufficient for trafficking to the INM. Tolerance for different linker lengths and protein conformations suggests that INM trafficking rules might differ from those in opisthokonts. The INM proteins developed here can be used to target new functionalities to the plant nuclear periphery.
Mitosis and meiosis in higher plants involves significant reconfiguration of the nuclear envelope and the proteins that interact with it. The dynamic series of events involves a range of interactions, movement, breakdown and reformation of this complex system. Recently, progress has been made in identifying and characterising the protein and membrane interactome that performs these complex tasks, including constituents of the nuclear envelope, the cytoskeleton, nucleoskeleton and chromatin. This review will present current understanding of these interactions and advances in knowledge of the processes for the breakdown and reformation of the nuclear envelope during cell divisions in plants.
Protein targeting to the inner nuclear membrane (INM) is one of the least understood protein targeting pathways. INM proteins are important for chromatin organization, nuclear morphology and movement, and meiosis, and have been implicated in human diseases. In opisthokonts, one mechanism for INM targeting is transport factor-mediated trafficking, in which nuclear localization signals (NLSs) function in nuclear import of transmembrane proteins. To explore whether this pathway exists in plants, we fused the SV40 NLS to a plant ER tail-anchored protein and showed that the GFP-tagged fusion protein was significantly enriched at the nuclear envelope (NE) of leaf epidermal cells. Airyscan subdiffraction limited confocal microscopy showed that this protein displays a localization consistent with an INM protein. Nine different monopartite and bipartite NLSs from plants and opisthokonts, fused to a chimeric tail-anchored membrane protein, were all sufficient for NE enrichment, and both monopartite and bipartite NLSs were sufficient for trafficking to the INM. Tolerance for different linker lengths and protein conformations suggests that INM trafficking rules might differ from those in opisthokonts. The INM proteins developed here can be used to target new functionalities to the plant nuclear periphery.
The movement of chromosomes during meiosis involves location of their telomeres at the inner surface of the nuclear envelope. Sad1/UNC-84 (SUN) domain proteins are inner nuclear envelope proteins that are part of complexes linking cytoskeletal elements with the nucleoskeleton, connecting telomeres to the force-generating mechanism in the cytoplasm. These proteins play a conserved role in chromosome dynamics in eukaryotes. Homologues of SUN domain proteins have been identified in several plant species. In Arabidopsis thaliana, two proteins that interact with each other, named AtSUN1 and AtSUN2, have been identified.
Immunolocalization using antibodies against AtSUN1 and AtSUN2 proteins revealed that they were associated with the nuclear envelope during meiotic prophase I. Analysis of the double mutant Atsun1-1 Atsun2-2 has revealed severe meiotic defects, namely a delay in the progression of meiosis, absence of full synapsis, the presence of unresolved interlock-like structures, and a reduction in the mean cell chiasma frequency. We propose that in Arabidopsis thaliana, overlapping functions of SUN1 and SUN2 ensure normal meiotic recombination and synapsis.
In non-plant systems, chromatin association with the nuclear periphery affects gene expression, where interactions with nuclear envelope proteins can repress and interactions with nucleoporins can enhance transcription. In plants, both hetero- and euchromatin can localise at the nuclear periphery, but the effect of proximity to the nuclear periphery on gene expression remains largely unknown. This study explores the putative function of Seh1 and Nup50a nucleoporins on gene expression by using the Lac Operator / Lac Repressor (LacI-LacO) system adapted to Arabidopsis thaliana. We used LacO fused to the luciferase reporter gene (LacO:Luc) to investigate whether binding of the LacO:Luc transgene to nucleoporin:LacI protein fusions alters luciferase expression. Two separate nucleoporin-LacI-YFP fusions were introduced into single insert, homozygous LacO:Luc Arabidopsis plants. Homozygous plants carrying LacO:Luc and a single insert of either Seh1-LacI-YFP or Nup50a-LacI-YFP were tested for luciferase activity and compared to plants containing LacO:Luc only. Seh1-LacI-YFP increased, while Nup50a-LacI-YFP decreased luciferase activity. Seh1-LacI-YFP accumulated at the nuclear periphery as expected, while Nup50a-LacI-YFP was nucleoplasmic and was not selected for further study. Protein and RNA levels of luciferase were quantified by western blotting and RT-qPCR, respectively. Increased luciferase activity in LacO:Luc+Seh1-LacI-YFP plants was correlated with increased luciferase protein and RNA levels. This change of luciferase expression was abolished by disruption of LacI-LacO binding by treating with IPTG in young seedlings, rosette leaves and inflorescences. This study suggests that association with the nuclear periphery is involved in the regulation of gene expression in plants.
SUN-domain proteins belong to a gene family including classical Cter-SUN and mid-SUN subfamilies differentiated by the position of the SUN domain within the protein. Although present in animal and plant species, mid-SUN proteins have so far remained poorly described. Here, we used a combination of genetics, yeast two-hybrid and in planta transient expression methods to better characterize the SUN family in Arabidopsis thaliana. First, we validated the mid-SUN protein subfamily as a monophyletic group conserved from yeast to plant. Arabidopsis Cter-SUN (AtSUN1 and AtSUN2) and mid-SUN (AtSUN3 and AtSUN4) proteins expressed as fluorescent protein fusions are membrane-associated and localize to the nuclear envelope (NE) and endoplasmic reticulum. However, only the Cter-SUN subfamily is enriched at the NE. We investigated interactions in and between members of the two subfamilies and identified the coiled-coil domain as necessary for mediating interactions. The functional significance of the mid-SUN subfamily was further confirmed in mutant plants as essential for early seed development and involved in nuclear morphology. Finally, we demonstrated that both subfamilies interact with the KASH domain of AtWIP1 and identified a new root-specific KASH-domain protein, AtTIK. AtTIK localizes to the NE and affects nuclear morphology. Our study indicates that Arabidopsis Cter-SUN and mid-SUN proteins are involved in a complex protein network at the nuclear membranes, reminiscent of the LInker of Nucleoskeleton and Cytoskeleton (LINC) complex found in other kingdoms.
Following the description of SAD1/UNC84 (SUN) domain proteins in higher plants, evidence has rapidly increased that plants contain a functional linker of nucleoskeleton and cytoskeleton (LINC) complex bridging the nuclear envelope (NE). While the SUN domain proteins appear to be highly conserved across kingdoms, other elements of the complex are not and some key components and interactions remain to be identified. This mini review examines components of the LINC complex, including proteins of the SUN domain family and recently identified plant Klarsicht/Anc/Syne-1 homology (KASH) domain proteins. First of these to be described were WIPs (WPP domain interacting proteins), which act as protein anchors in the outer NE. The plant KASH homologs are C-terminally anchored membrane proteins with the extreme C-terminus located in the nuclear periplasm; AtWIPs contain a highly conserved X-VPT motif at the C-terminus in contrast to PPPX in opisthokonts. The role of the LINC complex in organisms with a cell wall, and description of further LINC complex components will be considered, together with other potential plant-specific functions.
Inner nuclear membrane Sad1/UNC-84 (SUN) proteins interact with outer nuclear membrane (ONM) Klarsicht/ANC-1/Syne homology (KASH) proteins, forming linkers of nucleoskeleton to cytoskeleton conserved from yeast to human and involved in positioning of nuclei and chromosomes. Defects in SUN-KASH bridges are linked to muscular dystrophy, progeria, and cancer. SUN proteins were recently identified in plants, but their ONM KASH partners are unknown. Arabidopsis WPP domain interacting proteins (AtWIPs) are plant-specific ONM proteins that redundantly anchor Arabidopsis RanGTPase-activating protein 1 (AtRanGAP1) to the nuclear envelope (NE). In this paper, we report that AtWIPs are plant-specific KASH proteins interacting with Arabidopsis SUN proteins (AtSUNs). The interaction is required for both AtWIP1 and AtRanGAP1 NE localization. AtWIPs and AtSUNs are necessary for maintaining the elongated nuclear shape of Arabidopsis epidermal cells. Together, our data identify the first KASH members in the plant kingdom and provide a novel function of SUN-KASH complexes, suggesting that a functionally diverged SUN-KASH bridge is conserved beyond the opisthokonts.
The biogenesis and positioning of organelles involves complex interacting processes and precise control. Progress in our understanding is being made rapidly as advances in analysing the nuclear and organellar genome and proteome combine with developments in live-cell microscopy and manipulation at the subcellular level. This paper introduces the collected papers resulting from Organelle Biogenesis and Positioning in Plants, the 2009 Biochemical Society Annual Symposium. Including papers on the nuclear envelope and all major organelles, it considers current knowledge and progress towards unifying themes that will elucidate the mechanisms by which cells generate the correct complement of organelles and adapt and change it in response to environmental and developmental signals.
Controlled movement Of the nucleus is important in a wide variety of plant cellular events Positioning involving intact nuclei occurs in cell division, development, tip growing systems such as the root hair and in response to stimuli, including light, touch and infection. Positioning is also essential in the division and replication of nuclear components, ranging from chromosome attachment to the breakdown and reformation of the nuclear envelope. Although description and understanding of the processes involved have advanced rapidly in recent years, significant gaps remain in our knowledge, especially concerning nuclear proteins involved in anchoring and interacting with cytoskeletal and nucleoskeletal elements involved in movement. In the present review, processes involving the movement and positioning of nuclei and nuclear components are described together with novel proteins implicated in nucleoskeletal and cytoskeletal interactions.
Sad1/UNC-84 (SUN)-domain proteins are inner nuclear membrane (INM) proteins that are part of bridging complexes linking cytoskeletal elements with the nucleoskeleton, and have been shown to be conserved in non-plant systems. In this paper, we report the presence of members of this family in the plant kingdom, and investigate the two Arabidopsis SUN-domain proteins, AtSUN1 and AtSUN2. Our results indicate they contain the highly conserved C-terminal SUN domain, and share similar structural features with animal and fungal SUN-domain proteins including a functional coiled-coil domain and nuclear localization signal. Both are expressed in various tissues with AtSUN2 expression levels relatively low but upregulated in proliferating tissues. Further, we found AtSUN1 and AtSUN2 expressed as fluorescent protein fusions, to localize to and show low mobility in the nuclear envelope (NE), particularly in the INM. Deletion of various functional domains including the N terminus and coiled-coil domain affect the localization and increase the mobility of AtSUN1 and AtSUN2. Finally, we present evidence that AtSUN1 and AtSUN2 are present as homomers and heteromers in vivo, and that the coiled-coil domains are required for this. The study provides evidence suggesting the existence of cytoskeletal-nucleoskeletal bridging complexes at the plant NE.
A GFP fusion to the N-terminal 238 amino acids of the mammalian lamin B receptor (LBR) localises to the nuclear envelope (NE) when expressed in Nicotiana tabacum plants, showing properties expected of a native plant NE protein. In this study, we have used this chimaeric construct to explore evidence for common mechanisms of NE targeting and retention between plants and animals, given there is no plant homologue of the mammalian LBR or of one of its binding partners, lamin B. Binding mutants of LBR-GFP were created and fluorescence recovery after photobleaching of mutant and wild type constructs employed to examine their retention in the plant NE. Unmutated LBR-GFP was significantly less mobile in the NE than the lamin binding domain deletion mutant, which was also localised to theER and punctate structures in some cells. Mutation of the chromatin binding domain resulted in localisation of the protein in nuclear inclusions, in which it was immobile. Our findings, that expression of truncated LBR-GFP in plant cells results in altered targeting and retention relative to wt LBR-GFP, suggest that plant cells can recognize the INM-targeting motif of LBR. Altered mobility of the truncated probe indicates that not only do plant cells recognize this signal, but also have nuclear proteins that interact weakly with LBR.
The nuclear envelope (NE) is a double membrane system consisting of the inner nuclear envelope (INE), the outer nuclear envelope (ONE) and nuclear pore complexes (NPCs). Most of our knowledge about the NE proteome comes from studies in animal systems. Recent investigations in plant systems have shown that plants do not have homologues for the majority of animal NE proteins. In a previous study in our laboratory, a construct consisting of the N-terminus of the human lamin B receptor (LBR) fused to GFP was shown to target the plant INE. In mammalian cells, LBR is an intrinsic INE protein, whose targeting to the INE is facilitated by a nuclear localization signal and retention in the INE is achieved by LBR binding mainly to chromatin and lamins. In this study the targeting and retention of LBR–GFP in the plant NE has been investigated by introducing mutations in key domains of LBR and employing fluorescence recovery after photobleaching experiments. Mutation of the chromatin binding domain caused LBR to accumulate in nuclear inclusions in which it was immobile. Deletion of the lamin binding domain resulted in the construct being localized not only to the NE but also ER and to be significantly more mobile then the wild type LBR–GFP in the NE. In the case of both the lamin binding deletion and wild type LBR–GFP, mobility was found to be much greater than previously described in mammalian cells. (Abstracts of the Annual Main Meeting of the Society for Experimental Biology, Glasgow, Scotland, 31st March - 4th April, 2007)
Background information. In a previous study, we showed that GFP (green fluorescent protein) fused to the N-terminal 238 amino acids of the mammalian LBR (lamin B receptor) localized to the NE (nuclear envelope) when expressed in the plant Nicotiana tabacum. The protein was located in the NE during interphase and migrated with nuclear membranes during cell division. Targeting and retention of inner NE proteins requires several mechanisms: signals that direct movement through the nuclear pore complex, presence of a transmembrane domain or domains and retention by interaction with nuclear or nuclear-membrane constituents.
Quality control in the secretory pathway is a fundamental step in preventing deleterious effects that may arise by the release of malfolded proteins into the cell or apoplast. Our aims were to visualise and analyse the disposal route followed by aberrant proteins within a plant cell in vivo using fluorescent protein technology. A green fluorescent protein (GFP) fusion was detected in the cytosol and the nucleoplasm in spite of the presence of an N-terminal secretory signal peptide. In contrast to secreted GFP, the fusion protein was retained in the cells where it was degraded slowly, albeit at a rate much higher than that of the endoplasmic reticulum (ER)-retained derivative GFP-HDEL. The fusion protein could not be stabilised by inhibitors of transport or the cytosolic proteasome. However, the protein is a strong lumenal binding protein (BiP) ligand. Complete signal peptide processing even after long-term expression in virus-infected leaves rules out the possibility that the documented accumulation in the cytosol and nucleoplasm is because of the bypassing of the translocation pores. The data are consistent with the hypothesis that the fusion protein is disposed off from the ER via a retrograde translocation back to the cytosol. Moreover, accumulation in the nucleoplasm was shown to be microtubule dependent unlike the well-documented diffusion of cytosolically expressed GFP into the nucleoplasm. The apparent active transport of the GFP fusion into the nucleoplasm may indicate an as yet undiscovered feature of the ER-associated degradation (ERAD) pathway and explain the insensitivity to degradation by proteasome inhibitors.
Three-week-old Picea abies seedlings were grown for 7 days in 100 muM aluminium (AI), combined with 1000 or 2000 muM silicon (Si). Solution pH was adjusted to 4,00, 4.25, 4.50, 4.75, or 5.00. In the absence of Si, solution pH had no effect on the decrease in root growth caused by 100 muM Al. Silicon did not ameliorate toxic effects of Al on root growth at pH 4.00, 4.25 and 4.50, whereas significant, and apparently complete, amelioration was found at pH 4.75 and 5.00. An equilibrium speciation model (EQ3NR), with a current thermodynamic database, was used to predict the behaviour of Al and Si in growth solutions. When Si was not present in the 100 muM Al solutions, Al3+ declined from 92.4% of total Al at pH 4.00 to 54.6% at pH 5.00, and there was a concomitant increase in hydroxyaluminium species as pH increased. The addition of 1000 muM Si to the 100 muM At solutions caused a reduction in Al3+ content over the whole pH range: at pH 4.00 Al3+ fell from 92.4 to 83.3% in the presence of Si; and at pH 5.00 the fall was from 54.6 to 17.7%. These falls were attributed to the formation of hydroxyaluminosilicate (HAS) species. Similar, but somewhat greater, changes were observed in solutions containing 2000 muM Si. The match between root growth observations and the modelling data was not very good. Modelling predicted that change in Al3+ content with pH in the presence of Si was gradual, but root growth was markedly increased between pH 4.50 and 4.75. Differences between root growth and modelling data may be due to the model not correctly predicting solution chemistry or to in planta. effects which override the influence of solution chemistry. (C) 2003 Elsevier Inc. All rights reserved.
Aerenchyma formation in roots of maize (Zea mays L.) involves programmed death of cortical cells that is promoted by exogenous ethylene (1 µL L−1) or by endogenous ethylene produced in response to external oxygen shortage (3%, v/v). In this study, evidence that degeneration of the cell wall accompanies apoptotic-like changes previously observed in the cytoplasm and nucleus (Gunawardena et al. Planta 212, 205–214, 2001), has been sought by examining de-esterified pectins (revealed by monoclonal antibody JIM 5), and esterified pectins (revealed by monoclonal antibody JIM 7). In controls, de-esterified wall pectins were found at the vertices of triangular junctions between cortical cells (untreated roots). Esterified pectins in control roots were present in the three walls bounding triangular cell-to-cell junctions. After treatment with 3% oxygen or 1 µL L−1 ethylene, this pattern was lost but walls surrounding aerenchyma gas spaces became strongly stained. The results showed that cell wall changes commenced within 0·5 d and evidently were initiated by ethylene in parallel with cytoplasmic and nucleoplasmic events associated with classic intracellular processes of programmed cell death.
In plant cells, the organization of the Golgi apparatus and its interrelationships with the endoplasmic reticulum differ from those in mammalian and yeast cells. Endoplasmic reticulum and Golgi apparatus can now be visualized in plant cells in vivo with green fluorescent protein (GFP) specifically directed to these compartments. This makes it possible to study the dynamics of the membrane transport between these two organelles in the living cells. The GFP approach, in conjunction with a considerable volume of data about proteins participating in the transport between endoplasmic reticulum and Golgi in yeast and mammalian cells and the identification of their putative plant homologues, should allow the establishment of an experimental model in which to test the involvement of the candidate proteins in plants. As a first step towards the development of such a system, we are using Sar1, a small G-protein necessary for vesicle budding from the endoplasmic reticulum. This work has demonstrated that the introduction of Sar1 mutants blocks the transport from endoplasmic reticulum to Golgi in vivo in tobacco leaf epidermal cells and has therefore confirmed the feasibility of this approach to test the function of other proteins that are presumably involved in this step of endo-membrane trafficking in plant cells.
Aerenchyma is a tissue type characterised by prominent intercellular spaces which enhance flooding tolerance in some plant species by facilitating gas diffusion between roots and the aerial environment. Aerenchyma in maize roots forms by collapse and death of some of the cortical cells in a process that can be promoted by imposing oxygen shortage or by ethylene treatment. Maize roots grown hydroponically in 3% oxygen, 1 μl l−1 ethylene or 21% oxygen (control) were analysed by a combination of light and electron microscopy. Use of in-situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) suggested internucleosomal cleavage of DNA. However, chromatin condensation detectable by electron microscopy was preceded by cytoplasmic changes including plasma membrane invagination and the formation of vesicles, in contrast to mammalian apoptosis in which chromatin condensation is the first detectable event. Later, cellular condensation, condensation of chromatin and the presence of intact organelles surrounded by membrane resembling apoptotic bodies were observed. All these events were complete before cell wall degradation was apparent. Therefore, aerenchyma formation initiated by hypoxia or ethylene appears to be a form of programmed cell death that shows characteristics in part resembling both apoptosis and cytoplasmic cell death in animal cells.
Aluminium (Al) toxicity is a very important Factor limiting the growth of plants on acidic soils. Recently, a number of workers have shown that. under certain conditions, silicon (Si) can ameliorate the toxic effects of Al in hydroponic culture. The mechanism of the amelioration is unclear, but three suggestions have been put forward. Si-induced increase in solution pH during the preparation of hydroponic solutions. reduced availability of Al due to the formation of hydroxyaluminosilicate (HAS) species in those solutions during plant growth; or in planta detoxification. It is now known that it is possible to make up Al and Si solutions in an order in which pH is lowered prior to Al addition; in these cases amelioration has still been observed. Amelioration has also been noted in experiments where HAS formation is minimal. These observations would suggest that, at least under some circumstances, there is an in planta component to the amelioration phenomenon. Several microanalytical investigations have noted codeposition of Al and Si in root cell walls. We propose a model in which root cell walls are the main internal sites of aluminosilicate (AS) and/or HAS formation and of Al detoxification. Factors promoting AS/HAS formation in this compartment include: high apoplastic pH; the presence of organic substances (e.g. malate); and the presence of suitable local concentrations of reactive forms of Al and Si, on or within the surfaces of the wall matrix. All these are likely to be important in the amelioration of Al toxicity.
Two wheat (Triticum aestivum L.) cultivars, one aluminium tolerant (Atlas 66) and one sensitive (Scout 66), were grown in a continuous-flow culture system (less than or equal to pH 5.0) containing aluminium (0-100 mu M) and silicon (0-2000 mu M) in factorial combination. Treatment with silicon resulted in a highly significant amelioration of aluminium toxicity as assessed by root growth in both cultivars. Amelioration was influenced by wheat cultivar and silicon concentration, as 2000 mu M silicon significantly ameliorated the toxic effects of 100 mu M aluminium in Atlas 66, and only 5 mu M silicon alleviated the effect of 1.5 mu M aluminium on Scout 66. Nutrient medium pH was critical, as an amelioration by silicon was apparent only at pH > 4.2 for Atlas 66, and at pH > 4.6 for Scout 66. Silicon neither reduced levels of toxic aluminium species in the growth solutions, nor the amount of aluminium taken up by roots. In experiments to assess exudation of malate by Atlas 66 roots treated with 100 mu M aluminium, the presence of 2000 mu M silicon (pH 4.6) was found to have a negligible effect on exudation. In contrast, citrate, a known aluminium chelator, reduced aluminium-induced exudation of malate at 5-40 mu M and completely inhibited it at 100 mu M citrate. The results indicate that silicon does not reduce aluminium phytotoxicity as a result of aluminium/silicon interactions in the external media, and that the mechanism of amelioration has an in planta component.
Three treatments were selected for a microanalytical investigation of the basal third of the root, and the zone 3.5 mm behind the root tip: 2800 mu mol L-1 Si; 75 mu mol L-1 Al; and a combination of the two. When plants were grown in 2800 mu mol L-1 Si the major silica deposition sites in the roots were the endodermal walls. In the 75 mu mol L-1 Al treatment, Al was mainly located in the epidermal and hypodermal walls. Al treatment caused a leakage of phosphorus into these cell walls. When both 2800 mu mol L-1 Si and 75 mu mol L-1 Al were present in the nutrient solution, only Si was deposited in the endodermal walls, while both elements were present in the epidermal walls. Leakage of phosphorus appeared to be prevented in the presence of Si.
The response of seedlings of the monocot Hordeum vulgare L. cv. Bronze to 0,25 and 50 mu M aluminium in factorial combination with 0, 1.4, 2.0 and 2.8 mM Si was tested in hydroponic culture at pH 4.5. Nutrient solution (500 mu M calcium nitrate) and Al/Si treatments were designed to avoid the precipitation of Al from solution. Silicon treatments gave significant amelioration of the toxic effects of Al on root and shoot growth and restored calcium levels in roots and shoots at harvest to levels approaching those of control plants. Aluminium uptake by roots was also significantly diminished in the presence of Si. Silicon alone gave a slight stimulation of growth, insufficient to explain its ameliorative effect on Al toxicity. The mechanism of the Si effect on Al toxicity in monocotyledons awaits further investigation.
Aluminium and silicon are usually abundant in soil mineral matter, but their availability for plant uptake is limited by low solubility and, in the case of Al, high soil pH causes precipitation of the element: in insoluble forms. Al toxicity is a major problem in naturally occurring acid soils and in soils affected by acidic precipitation. Al has no known role in higher plants, and is generally known as a toxic element, whereas Si is generally regarded as a beneficial element. Recently, it has been suggested that Al toxicity can be ameliorated by Si in a variety of animal systems. In this review the evidence that amelioration of Al toxicity by Si can also occur in plants is assessed. At present such amelioration has been shown in sorghum, barley, teosinte, and soybean, but not in rice, wheat, cotton, and pea. Plant species vary considerably in the amounts of Al and Si that they transport into their tissues, and it seems that very high Si accumulation and very high Al accumulation are mutually exclusive. The mechanisms considered for amelioration are: solution effects; codeposition of Al and Si within the plant; effects in the cytoplasm and on enzyme activity; and indirect effects.
The analysis of nuclear envelope components and their function has recently been progressed by the use of computational methods of analysis. The methods in this chapter provided by members of the International Plant Nucleus Consortium address the identification of novel nuclear envelope proteins and the study of structure and mobility of the nucleus. DORY2 is an upgrade of the KASH-finder DORY, and NucleusJ is used to characterize the three-dimensional structure of the nucleus in light microscope images. Finally, a method is provided for analysis of the migration of the nucleus, a key technique for exploring the function of plant nuclear proteins.
The nuclear envelope (NE) is a double membrane system that forms a protective barrier around chromatin and organises intranuclear structures and activities. The outer nuclear membrane (ONM) is continuous with the ER and associates with cytoskeletal elements. The inner nuclear membrane (INM) interacts with chromatin and the nucleoskeleton and plays a fundamental role in orchestrating nuclear functions such as nucleic acid metabolism. Most of our knowledge of the NE proteome and its functions comes from studies in animal systems. Despite its importance, the plant NE remains poorly understood. Here we present the characterisation of two novel NE proteins, AtSUN1 and AtSUN2, plant homologues of a group of animal and yeast INM proteins containing a well conserved SUN (Sad1/UNC84 homology) domain important for nucleo-cytoskeletal linkage. Both proteins share a similar domain layout to their animal counterparts and appear to interact with each other as indicated by fluorescence resonance energy transfer. Confocal microscopy of fluorescent protein fusions and electron microscopy suggest localisation to the plant INM. Deletion of either the SUN domain or a nuclear localisation signal abolishes this localisation. These SUN domain proteins are the first true inner nuclear envelope proteins to be identified in plants and provide the first evidence for a plant Linker of Cytoskeleton and Nucleoskeleton Complex.
Mitosis and Nuclear Structure, 2013. Company of Biologists Wiston House Conference.
International Plant Nucleus Consortium annual meeting, Olamouc, Czech Republic 2015
Society for Experimental Biology 'Nuclear Dynamics' conference co-organiser, Brighton, 2016
Society for Experimental Biology Annual Main Meeting, Nuclear Dynamics Special Interest Group, Firenze 2018
Indepth Kick-Off meeting, Clermont Ferrand, France, 2018
Indepth Management Meeting and Conference, Praha, 2019
SEB Annual Main Meeting and Special Interest Group session, Praha 2020
1983-1988 Botany Fellow Department of Plant Sciences, University of Oxford (Junior research fellow, Wolfson College, Oxford, 1984-1988)
1988-1998 Royal Society University Research Fellow (Research Fellow, Wolfson College, Oxford, 1989-1992)
1989-1990 Stipendiary Lecturer, Magdalen College Oxford (1 year temporary post)
Honorary Secretary of the Cell Biology Section of the Society for Experimental Biology (2003- 2008)
International Plant Nucleus Consortium
Indepth COST Action
International Plant Nucleus Consortium Web Resources