1,721,052 research outputs found
Cellular mechanisms for heavy metal detoxification and tolerance
No full textHeavy metals such as Cu and Zn are essential for normal plant growth, although elevated concentrations of both essential and non-essential metals can result in growth inhibition and toxicity symptoms. Plants possess a range of potential cellular mechanisms that may be involved in the detoxification of heavy metals and thus tolerance to metal stress. These include roles for the following: for mycorrhiza and for binding to cell wall and extracellular exudates; for reduced uptake or efflux pumping of metals at the plasma membrane; for chelation of metals in the cytosol by peptides such as phytochelatins; for the repair of stress-damaged proteins; and for the compartmentation of metals in the vacuole by tonoplast-located transporters. This review provides a broad overview of the evidence for an involvement of each mechanism in heavy metal detoxification and tolerance
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
Assimilate transport and partitioning in fungal biotrophic interactions
No full textThere are two major fungal biotrophic interactions with higher plants: pathogenic biotrophs such as mildews and rusts that cause substantial losses in crop yields, and mutualistic fungi that form mycorrhizas and aid the uptake of phosphate and other minerals from the soil with considerable agronomic benefits. Both are dependent on the plant for the supply of carbon, yet much remains to be resolved concerning the transport and partitioning of photoassimilates in these associations. In both associations, specialised membranes interfaces are formed which are considered to be the primary sites of nutrient transfer between plant and fungus. A range of solutes may cross these interfaces, although glucose appears to have a particularly important role. Molecular techniques are being used to identify the specific membrane transporters involved at the interface. The establishment of these biotrophic inter-actions also has a major effect on the metabolism and transport activity of the host plant that affects its source–sink balance. Increases in certain invertase activities and in hexose transporters are especially marked. Again, the introduction of molecular biology to these problems is beginning to provide the information on the cellular locations and coordination of these host cell responses that is required in order to understand how partitioning is regulated in these plant fungal interactions
ATPase and proton pumping activities in cotyledons and other phloem-containing tissues2<i>Ricinus communis</i>
No full textATPase activity was investigated in phloem-containing tissues of Ricinus communis in relation to its proposed role in phloem loading. Cytochemical staining of cotyledons revealed an ATP-hydrolysing activity on the plasma membrane of the sieve tube/companion cell complex. Microsomal fractions prepared from cotyledons and main veins contained a Mg2+-dependent ATPase activity which showed low stimulation by KC1 particularly at pH 6.5. The pH optimum was at pH 8.5 to 90, although the effect of azide indicated the presence of mitochondrial ATPase. At pH 6.5, the cited optimum for plasma membrane ATPase, the activity showed strong inhibition by PCMBS, vanadate and DCCD. A high pyrophosphatase activity was observed at pH 8.5. Acidification of the medium by intact cotyledons was increased by fusicoccin and inhibited by PCMBS, NEM and vanadate. Proton pumping by microsomal vesicles as measured by quinacrine fluorescence was also inhibited by PCMBS, NEM and vanadate. Sucrose uptake by cotyledon discs showed strong inhibition by PCMBS, NEM and CCCP but was little affected by vanadate. Sucrose uptake varied with the developmental stage of the cotyledons and this correlated with microsomal ATPase activity measured at pH 6.5, although the precise cellular origin of this activity is not certain. The results are discussed in relation to the role of ATPase activity and proton pumping in phloem loading
Solubilization, reconstitution and characterization of vanadate-sensitive, ATP-driven H+ -transport from cotyledons of <i>Ricinus communis</i>
No full textATPase and proton-translocating activities in a plasma membrane-enriched fraction from cotyledons of <i>Ricinus communis</i>
No full textSucrose gradient centrifugation was used to separate the microsomal membranes and purify the plasma membrane ATPase from Ricinus cotyledons. The pellet from a three-step (30, 34, 38%) sucrose gradient was enriched in plasma membrane as determined by a combination of marker assays.The partially purified plasma membrane ATPase was magnesium-dependent and had a pH optimum of 6.5. It showed high sensitivity to vanadate, erythrosin B, SW 26, DCCD and PCMBS but low sensitivity to azide, nitrate and NEM. Substitution of calcium for magnesium resulted in low activity, and in the presence of magnesium, calcium was inhibitory. KCl stimulation was low (less than 50%) and of the potassium salts tested all were stimulatory except HCO−3 which was inhibitory. Specificity for nucleotide triphosphates was high, greatest activity occurring with ATP.Proton-pumping activity measured using quinacrine fluorescence quenching was inhibited by vanadate and erythrosin B but not by nitrate and oligomycin indicating that activity was mainly due to the plasma membrane ATPase
Chromatographie resolution, purification and characterization of H+-PPase and H+-ATPase from Ricinus cotyledons
No full textInorganic pyrophosphatase (PPase) was purified from membrane fractions isolated from Ricinus cotyledons. The non-ionic detergent dodecyl-ß-D-maltoside (lauryl maltoside) was used to solubilise the PPase from the phase-partitioned, upper phase fraction (plasma membrane-enriched), and purification was achieved using a combination of ion exchange chromatography and gel filtration. The PPase was resolved from the plasma membrane ATPase by exploiting the greater phospholipid dependency of elution of the PPase from a 300 SW gel filtration column. When the phospholipid concentration in the elution buffer was 0.5 mg/mL the PPase and ATPase eluted together but when it was lowered ten-fold the enzymes were resolved. The purification procedure resulted in an approximately 30-fold purification of the PPase from the original upper phase membranes with a yield of 20–25 %. The final purified fraction was enriched in a protein with an apparent molecular mass of 68 kDa which cross-reacted with an antibody raised to the mung bean tonoplast PPase. The purified PPase activity was markedly stimulated by potassium salts and inhibited by sodium fluoride, methylene diphosphonate, N,N′-dicyclohexylcarbodiimide and N-ethyl-maleimide with no significant inhibition by azid
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
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