1,721,007 research outputs found
Transition metal transporters in plants
No full textTransition metals such as Fe, Cu, Mn, and Zn are essential minerals for normal plant growth and development, although they can be toxic when present in excess. Thus, for healthy plant growth, a range of transition metals must be acquired from the soil, distributed around the plant, and their concentrations carefully regulated within different cells and organelles. Membrane transport systems are likely to play a central role in these processes. The application of powerful genetic and molecular techniques has now identified a range of gene families that are likely to be involved in transition metal transport. These include the heavy metal ATPases (HMAs), the Nramps, the cation diffusion facilitator (CDF) family, the ZIP family, and the cation antiporters. This review provides a broad overview of the range of potential transport systems now thought to be involved in the uptake, distribution and homeostasis of transition metals in plants
Changes in the expression pattern of the plasma membrane H+-ATPase in developing Ricinus communis cotyledons undergoing the sink/source transition
No full textThe plasma membrane (PM) H+-ATPase is thought to play a key role in generating the proton motive force used to drive the uptake and accumulation of solutes in plant cells. Changes in its expression pattern were studied in the Ricinus communis L. cotyledon as it changed from a sink to a source organ. Expression was monitored in 3-, 10- and 14-day-old cotyledons using an antibody to the maize PM H+-ATPase. The antibody labelled a 100-kDa protein in membrane fractions prepared from cotyledons and this protein occurred at higher levels in the PM-enriched fractions compared to those enriched in intracellular membranes. Immunostaining of tissue sections of 3-day-old Ricinus cotyledons (sinks) with this antibody demonstrated that the PM H+-ATPase was highly expressed in the lower epidermal cells and also in the vascular bundles, particularly the phloem. The high expression in the epidermis suggests that these cells may be important in the initial active uptake of solutes from the endosperm. A similar distribution was observed in the 10-day-old seedlings but, in addition, larger, more spherical cells (idioblasts) had developed in the lower and upper epidermal layers and these were also labelled. In 14-day-old seedlings the cotyledons are no longer reliant on nutrients from the endosperm (which has totally degraded) and they are functioning as source organs. This is reflected in a decrease in PM H+-ATPase expression in the lower epidermal cells, apart from idioblasts and stomatal guard cells. The latter were also observed in the upper epidermis. Expression remained high in the vascular bundles of 14-day-old seedlings with strong staining in the phloem
P-type calcium ATPases in higher plants - biochemical, molecular and functional properties
No full textPlant and animal cells regulate cytosolic free calcium at sub-micromolar concentrations (see 1, 2 for reviews). This is achieved by a combination of active Ca2+ pumps (P-type ATPases) and antiports energised by the primary ion-motive pumps of the cell, together with regulated Ca2+-influx channels. In plants, the primary motive force for the transport of most solutes is provided by trans-membrane proton pumps located at the plasma membrane and vacuolar membrane (tonoplast); this contrasts with the sodium/potassium systems of mammalian cells (for a review, see [1]). Recently, a variety of studies have shown that plant cells contain several types of Ca2+-pumping ATPase, including those possessing a calmodulin-binding autoinhibitory domain and those lacking such a domain 2, 3, 4, 5. Molecular and biochemical evidence indicates similarities, but also key differences (particularly in subcellular locations) between plants and animals, e.g. 2, 3, 4, 5, 6.It is the aim of this review to draw together current molecular and related data indicating the structure, function and location of the various plant Ca2+ pumps and to compare these with their homologues from other organism
Characterization of a glutamine/proton cotransporter from ricinus-communis roots using isolated plasma-membrane vesicles
No full textEffects of air pollutants on proton and sucrose transport at the plasma membrane of <i>Ricinus communis</i>
No full textThe effects of the air pollutants O3, SO2 and NO2 on aspects of sucrose/proton cotransport across the plasma membrane of Ricinus communis plants have been investigated. The H+-ATPase hydrolytic activity in cotyledon plasma membrane vesicles purified by phase partitioning showed small stimulations by Na2SO3 or NaNO3 added separately or together to the assay medium. ATPase activity from plants pretreated by fumigation with SO2 or O3 also showed an increase, the effect of O3 being quite marked. Plasma membrane H+-pumping in KI-treated microsomal fractions and medium acidification by intact cotyledons both showed small decreases in the presence of Na2SO3 or NaNO2. Both Na2SO3 and NaNO2 at high concentrations (2 mol m–3) had significant effects on sucrose uptake by intact cotyledons, although sucrose efflux was unaffected. No significant effects on sucrose uptake or efflux by intact cotyledons were observed in plants pretreated by fumigation with SO2 or O3. Proton-coupled sucrose transport in isolated plasma membrane vesicles was inhibited in the presence of Na2SO3 or NaNO2. However, both pollutants also significantly inhibited the uptake of acetate by the vesicles, indicating a dissipation of the pH gradient across the membrane. It was concluded that no specific aspect of the sucrose/proton cotransport mechanism was damaged by these air pollutants, and that the effects of these pollutants on carbohydrate partitioning are more likely to be due to general effects on membrane integrity or on other aspects such as leaf carbohydrate metabolism
Effect of sw26 and erythrosin-b on atpase activity and related processes in ricinus cotyledons and cucumber hypocotyls
No full textThe herbicide SW26 and erythrosin B (EB) both inhibited ATPase activity in microsomal and plasma membrane-enriched fractions isolated from Ricinus cotyledons and cucumber hypocotyls. Both inhibitors were more effective with the vanadate-sensitive plasma membrane fraction.With intact tissues, EB was an effective inhibitor of both medium acidification and sucrose uptake by Ricinus cotyledons, whereas SW26 had no effect. EB was also a more effective inhihitor than SW26 of medium acidification and elongation growth by cucumber hypocotyls. Neither EB or SW26 affected tissue respiration.Thus, these reagents are useful additions to the limited range of inhibitors available to investigate the function of proton-pumping ATPases using both isolated membrane fractions and intact tissue
Two additional type IIA Ca2+-ATPases are expressed in Arabidopsis thaliana: evidence that type IIA sub-groups exist
No full textHigh affinity Ca2+-ATPases play a central role in calcium homeostasis by catalysing the active efflux of calcium from the cytoplasm. This study reports the identification of two additional type IIA (SERCA-type) Ca2+-ATPases from Arabidopsis (AtECA2 and AtECA3), and describes the detailed sequence analysis of these genes in comparison with AtECA1 and other plant and animal Ca2+-ATPases. Southern analysis suggests that each of these genes is present as a single copy and also that there may be a small family of moderately related genes that encode type IIA Ca2+-ATPases in Arabidopsis. Evidence is also provided from RT-PCR that these genes are expressed in Arabidopsis. Hydropathy analysis predicts that the topology of the Arabidopsis type IIA proteins is similar to the animal SERCA proteins. Sequence and phylogenetic analyses suggest that the type IIA Ca2+-ATPases can be further divided into sub-group
Further characterization of the red beet plasma-membrane ca-2+-atpase using gtp as an alternative substrate
No full textThe GTP-driven component of Ca2+ uptake in red beet (Beta vulgaris L.) plasma membrane vesicles was further characterized to confirm its association with the plasma membrane Ca2+-translocating ATPase and assess its utility as a probe for this transport system. Uptake of 45Ca2+ in the presence of GTP demonstrated similar properties to those previously observed for red beet plasma membrane vesicles utilizing ATP with respect to pH optimum, sensitivity to orthovanadate, dependence on Mg:substrate concentration and dependence on Ca2+ concentration. Calcium uptake in the presence of GTP was also strongly inhibited by erythrosin B, a potent inhibitor of the plant plasma membrane Ca2+-ATPase. Furthermore, after treatment with EGTA to remove endogenous calmodulin, the stimulation of 45Ca2+-uptake by exogenous calmodulin was nearly equivalent in the presence of either ATP or GTP. Taken together these results support the proposal that GTP-driven 45Ca2+ uptake represents the capacity of the plasma membrane Ca2+-translocating ATPase to utilize this nucleoside triphosphate as an alternative substrate. When plasma membrane vesicles were phosphorylated with [γ-32P]-GTP, a rapidly turning over, 100 kilodalton phosphorylated peptide was observed which contained an acyl-phosphate linkage. While it is proposed that this peptide could represent the catalytic subunit of the plasma membrane Ca2+-ATPase, it is noted that this molecular weight is considerably lower than the 140 kilodalton size generally observed for plasma membrane Ca2+-ATPases present in animal cell
Characterization of amino-acid-transport in ricinus-communis roots using isolated membrane-vesicles
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