ATPase Activity In Roots Research Articles

Boron deficiency affects ATP hydrolysis of plasma membrane and nutrients uptake in coffee: Consequences for plant growth

Boron (B) shapes the plasma membrane structure and modulates the plasma membrane H+-ATPase activity stimulating nutrients uptake by the plant root system. However, the influence of B-nutritional status on plasma membrane H+-ATPase activity of some plants remains unclear, especially in dicots with higher B requirement, such as coffee. This study investigated the effects of B-nutritional status on ATP hydrolysis of plasma membrane and nutrients uptake in coffee. Coffee seedlings were grown in substrate with six B levels (0.1, 0.2, 0.4, 0.6, 0.8 and 1.0 mg dm−3, as H3BO3) for 153 days and plasma membrane H+-ATPase activity was evaluated in the roots, as well as nutrient concentration and accumulation in leaf tissues and plant growth. The B nutritional status greatly influenced plasma membrane H+-ATPase activity in roots. At 1.0 mg dm−3, the ATPase hydrolysis activity was six times greater and H+ transport two times higher compared to the lowest level of 0.1 mg dm−3. The B supply increased significantly leaf concentrations of B, K, P, Mg, and Ca; nevertheless, accumulation of these nutrients did not vary in the leaves because leaf biomass decreased at high B levels.

NaCl-altered oxygen flux profiles and H+-ATPase activity in roots of two contrasting poplar species.

Maintaining mitochondrial respiration is crucial for proving ATP for H+ pumps to continuously exclude Na+ under salt stress. NaCl-altered O2 uptake, mitochondrial respiration and the relevance to H+-ATPase activity were investigated in two contrasting poplar species, Populus euphratica (salt-tolerant) and Populus popularis 35-44 (salt-sensitive). Compared with P. popularis, P. euphratica roots exhibited a greater capacity to extrude Na+ under NaCl stress (150mM). The cytochemical analysis with Pb(NO3)2 staining revealed that P. euphratica root cells retained higher H+ hydrolysis activity than the salt-sensitive poplar during a long term (LT) of increasing salt stress (50-200mM NaCl, 4weeks). Long-sustained activation of proton pumps requires long-lasting supply of energy (adenosine triphosphate, ATP), which is delivered by aerobic respiration. Taking advantage of the vibrating-electrodes technology combined with the use of membrane-tipped, polarographic oxygen microelectrodes, the species, spatial and temporal differences in root O2 uptake were characterized under conditions of salt stress. Oxygen uptake upon NaCl shock (150mM) was less declined in P. euphratica than in P. popularis, although the salt-induced transient kinetics were distinct from the drastic drop of O2 caused by hyperosmotic shock (255mM mannitol). Short-term (ST) treatment (150mM NaCl, 24h) stimulated O2 influx in P. euphratica roots, and LT-treated P. euphratica displayed an increased O2 influx along the root axis, whereas O2 influx declined with increasing salinity in P. popularis roots. The spatial localization of O2 influxes revealed that the apical zone was more susceptible than the elongation region upon high NaCl (150, 200mM) during ST and LT stress. Pharmacological experiments showed that the Na+ extrusion and H+-ATPase activity in salinized roots were correspondingly suppressed when O2 uptake was inhibited by a mitochondrial respiration inhibitor, NaN3. Therefore, we conclude that the stable mitochondrial respiration energized H+-ATPase of P. euphratica root cells for maintaining Na+ homeostasis under salt environments.

Ethylene Mediates Alkaline-Induced Rice Growth Inhibition by Negatively Regulating Plasma Membrane H+-ATPase Activity in Roots.

pH is an important factor regulating plant growth. Here, we found that rice was better adapted to low pH than alkaline conditions, as its growth was severely inhibited at high pH, with shorter root length and an extreme biomass reduction. Under alkaline stress, the expression of genes for ethylene biosynthesis enzymes in rice roots was strongly induced by high pH and exogenous ethylene precursor ACC and ethylene overproduction in etol1-1 mutant aggravated the alkaline stress-mediated inhibition of rice growth, especially for the root elongation with decreased cell length in root apical regions. Conversely, the ethylene perception antagonist silver (Ag+) and ein2-1 mutants could partly alleviate the alkaline-induced root elongation inhibition. The H+-ATPase activity was extremely inhibited by alkaline stress and exogenous ACC. However, the H+-ATPase-mediated rhizosphere acidification was enhanced by exogenous Ag+, while H+ efflux on the root surface was extremely inhibited by exogenous ACC, suggesting that ethylene negatively regulated H+-ATPase activity under high-pH stress. Our results demonstrate that H+-ATPase is involved in ethylene-mediated inhibition of rice growth under alkaline stress.

Distinct effect of pH on N uptake and assimilation in two conifer species

Prince Rupprecht’s Larch from the Loess Plateau takes up and assimilates a greater proportion of N as NO , particularly at neutral pH, whereas Chinese Fir assimilates a greater proportion of N as NH , particularly at low pH levels. The effects of pH on nitrate and ammonium uptake and assimilation in two coniferous species were compared. Prince Rupprecht’s Larch (Larix principis-rupprechtii Mayr) grows on the loess plateau in alkaline soils with low available nitrogen (N), whereas Chinese Fir (Cunninghamia lanceolata) grows in acidic soils. In the present study, the net fluxes in ammonium (NH4 +) and nitrate (NO 3 ) were measured using a non-invasive microelectrode ion flux measurement system, and the expression of NH4 + and NO 3 transporters (AMTs and NRTs, respectively) as well as H+-ATPase was examined to provide insights into the N uptake mechanisms in Prince Rupprecht’s Larch and Chinese Fir. The enzyme assays involved in N assimilation were also determined. For Prince Rupprecht’s Larch, low pH (pH 4) resulted in a decrease in net ammonium uptake, which remained unchanged in Chinese Fir. Net nitrate uptake in Prince Rupprecht’s Larch and Chinese Fir was much lower in soils with pH 4 relative to those with pH 7. Low pH significantly decreased the H+-ATPase activity and the expression level of NRTs in roots of Prince Rupprecht’s Larch. However, the expression level of AMTs in Prince Rupprecht’s Larch was significantly higher at pH 7 than at pH 4. The H+-ATPase activity in roots of Chinese Fir remained unaltered in response to changes in pH, and the transcript abundances of AMTs and NRTs were down-regulated by low pH. Low pH decreased N assimilation in both conifer species with the exception of NH4 + assimilation in Chinese Fir, which displayed higher glutamine synthetase (GS) and glutamate synthetase (GOGAT activities) at low pH. Prince Rupprecht’s Larch from the Loess Plateau takes up and assimilates a greater proportion of N as NO 3 , particularly at neutral pH, whereas Chinese Fir assimilates a greater proportion of N as NH4 +, particularly at low pH levels. This study contributes to our understanding of nitrogen metabolism mechanisms in response to pH changes.

Salicylic acid in plant salinity stress signalling and tolerance

Soil salinity is one of the major environmental stresses affecting crop production worldwide, costing over $27Bln per year in lost opportunities to agricultural sector and making improved salinity tolerance of crops a critical step for sustainable food production. Salicylic acid (SA) is a signalling molecule known to participate in defence responses against variety of environmental stresses including salinity. However, the specific knowledge on how SA signalling propagates and promotes salt tolerance in plants remains largely unknown. This review focuses on the role of SA in regulation of ion transport processes during salt stress. In doing this, we briefly summarise a current knowledge on SA biosynthesis and metabolism, and then discuss molecular and physiological mechanisms mediating SA intracellular and long distance transport. We then discuss mechanisms of SA sensing and interaction with other plant hormones and signalling molecules such as ROS, and how this signalling affects activity of sodium and potassium transporters during salt stress. We argue that NPR1-mediated SA signalling is pivotal for (1) controlling Na+ entry into roots and the subsequent long-distance transport into shoots, (2) enhancing H+-ATPase activity in roots, (3) preventing stress-induced K+ leakage from roots via depolarisation-activated potassium outward-rectifying channel (KOR) and ROS-activated non-selective cation channels, and (4) increasing K+ concentration in shoots during salt stress. Future work should focus on how SA can regulate Na+ exclusion and sequestration mechanisms in plants.

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO3−) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10mM HCO3− (−Fe+Bic and −Fe, respectively). After 21d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO3− (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO3− upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H+-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO3− prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.

Molecular Characterization of Mutant Arabidopsis Plants with Reduced Plasma Membrane Proton Pump Activity

Arabidopsis mutants containing gene disruptions in AHA1 and AHA2, the two most highly expressed isoforms of the Arabidopsis plasma membrane H(+)-ATPase family, have been isolated and characterized. Plants containing homozygous loss-of-function mutations in either gene grew normally under laboratory conditions. Transcriptome and mass spectrometric measurements demonstrate that lack of lethality in the single gene mutations is not associated with compensation by increases in RNA or protein levels. Selected reaction monitoring using synthetic heavy isotope-labeled C-terminal tryptic peptides as spiked standards with a triple quadrupole mass spectrometer revealed increased levels of phosphorylation of a regulatory threonine residue in both isoforms in the mutants. Using an extracellular pH assay as a measure of in vivo ATPase activity in roots, less proton secreting activity was found in the aha2 mutant. Among 100 different growth conditions, those that decrease the membrane potential (high external potassium) or pH gradient (high external pH) caused a reduction in growth of the aha2 mutant compared with wild type. Despite the normal appearance of single mutants under ideal laboratory growth conditions, embryos containing homozygous double mutations are lethal, demonstrating that, as expected, this protein is absolutely essential for plant cell function. In conclusion, our results demonstrate that the two genes together perform an essential function and that the effects of their single mutations are mostly masked by overlapping patterns of expression and redundant function as well as by compensation at the post-translational level.

Differences of Cu accumulation and Cu‐induced ATPase activity in roots of two populations of Elsholtzia haichowensis Sun

Two populations of Elsholtzia haichowensis, which are from an uncontaminated site (Hong'an) and a Cu mine site (Tonglushan) in Hubei province, China, were studied for ATPase activities and Cu accumulation of roots under hydroponic conditions. The root tolerance indices were markedly higher in Tonglushan population than in Hong'an population under Cu stress conditions. The root Cu concentration in Tonglushan population was significantly lower than that in Hong'an population in all Cu treatments. The Cu-stimulated ATPase activity increased significantly under 1 microM Cu, reached a peak at 5 microM Cu and then, began to decrease. However, no significant change of ATPase activity was observed in Hong'an population except for an obvious decrease in 80 microM Cu treatment. These results showed that Cu-ATPase might exist in the root plasma membrane of Tonglushan population and play a possible role in resistance to copper.

Shoot Apex Demand Determines Assimilate and Nutrients Partitioning and Nutrient‐uptake Rate in Tobacco Plants

Abstract Our previous experiment revealed that apex‐removed plants have larger root systems but a lower K+‐uptake rates than intact tobacco plants. Since the apex is not only a center of growth and metabolism, but also an important place of auxin synthesis and export, the aims of this study were to distinguish whether the apex demand or auxin synthesized in the apex regulates assimilate and nutrients partitioning within plant, and to explain the reason for the lower K+‐uptake rate of the apex‐removed plant. In comparison with the control plant, covering the shoot apex with a black transparent plastic bag reduced net increases in dry matter and nutrients; however, the distribution of the dry matter and nutrients between shoot and roots and nutrient‐uptake rates were not changed. Removal of the shoot apex shifted the dry mass and nutrients distributions to roots, and reduced the rate of nutrient uptake. Application of 1‐naphthylacetic acid (NAA) could partly replace the role of the removed apex, stimulated assimilate and nutrient deposition into the treated tissue, and enhanced the reduced plasma membrane ATPase activity of roots to the control level. However, treatment of the apex‐removed plants with NAA could not rescue the reduced nutrient uptake rate and the shifted assimilates and nutrients partitioning caused by excision of the apex. Higher nutrient uptake rate of the intact plants could not be explained by root growth parameters, such as total root surface area and number of root tips. The results from the present study indicate that strong apex demand determined assimilates and nutrients partitioning and nutrient‐uptake rate in tobacco (Nicotiana tabacum) plants.

Variations in salt tolerance of reed canarygrass (Phalaris arundinacea L.) plants grown at sites with different degrees of cattle urine contamination

Variations in the salt tolerance of reed canarygrass (RCG) plants grown at sites with different degrees of cattle urine contamination were investigated. Cattle urine overflowed the urine reservoir and invaded the grassland. Soils and RCG plants were collected from sampling spots selected along the urine flowing line from 0 (contaminated site beside the urine reservoir) to 100 m. With increasing distance from the reservoir, the contents of K, Na, Ca, Mg and NO3-N in the soil and Na, K and NO3-N in the collected RCG plants decreased. The RCG plants were grown in a standard solution to obtain a large number of clones and seeds for the next generation. After the RCG clones and their next generation were subjected to water culture to the fifth leaf stage, NaCl was applied to the solution to investigate their salt tolerance. The salt tolerance, which was the highest in the RCG clones and their next generation for the plants collected from the site beside the reservoir, decreased with increasing distance from the reservoir. Under saline water culture conditions, Na and free-proline contents in shoots, K content in shoots and roots, water potential of leaves and plasmalemma ATPase activity of roots increased in the RCG clones and their next generation along with a higher salt tolerance. In conclusion, responses to saline conditions were similar between the RCG clones and the next generation that were cross-pollinated. It was considered that, even within a confined range of the grassland, salt-tolerant RCG plants that had adapted to the urine-contaminated soils were selected, and that high salt tolerance was genetically controlled. It appears likely that the maintenance of the water potential and K-absorbing function under NaCl stress contributed to the high salt tolerance.

Flux of protons released by wild type and ferritin over-expressor tobacco plants : effect of phosphorus and iron nutrition

Tobacco ( Nicotiana tabacum) plants over-expressing the iron storage protein ferritin, either in the cytoplasm or in the plastids, were grown under various P and Fe conditions. The crossed effects of both the genotypes and the environmental conditions on iron and chlorophyll concentrations in leaves, ferric reductase (EC 1.6.99.13) and plasmalemma H +-ATPase (EC 3.6.3.6) activities in roots, and fluxes of H + released by roots were determined. The increase in leaf Fe concentration observed in plants over-expressing ferritin was accompanied by an increase in root ferric reductase and H +-ATPase activities. Iron deficient conditions induced a decrease in Fe and chlorophyll concentrations in leaves, an increase in ferric reductase and H +-ATPase activities in roots and an increase in H +-flux released by roots in all genotypes. Phosphorus abundant conditions induced also an increase in ferric reductase and H +-ATPase activities in roots in all genotypes, and an increase in H +-flux released by roots in the genotype over-expressing ferritin in the cytoplasm. These results suggest that P could regulate the root Fe uptake system, at the gene expression level, as already reported for Zn in barley. Moreover, they show that H +-flux was not always consistent with H +-ATPase activity, revealing that the global measurement of root plasmalemma H +-ATPase activity has some limits compared to the localized determination of the H +-flux. These limits could be due to the fact that part of the H +-flux is not directly linked to H +-ATPase activity in roots.

Development of freezing tolerance in roots and shoots of Scots pine seedlings at nonfreezing temperatures

The hardening of hydroponically cultured Scots pine (Pinus sylvestris L.) seedlings and their recovery after freezing was studied at the end of the second growing season (LD), after 3 weeks of short day treatment (SD), after a gradual decrease in temperature to 5°C over 4 weeks (H1), and after 4 weeks at 5°C (H2). Frost hardiness was determined by several methods and the recovery as survival of the seedlings. The highest frost hardiness was achieved in the distal parts of needles (-21 to -27°C) and in the proximal parts of needles (-18 to -25°C), followed by woody roots (-7 to -9°C), the 1-year-old and current stem (-8°C), and the fine roots (-5°C), all at the end of H2. Hardening of needles was induced by SD, but the stem and woody roots started to harden later, as a response to low temperature. As a result of frost treatment during LD and SD, potential plasma membrane roman H+-ATPase activity of roots decreased as electrolyte leakage increased and extracellular resistance decreased, but this relationship was lost during H1 and H2. The present study demonstrates the lack of hardening capacity in the fine roots of Scots pine seedlings at nonfreezing temperatures and the increased mortality of the young seedlings having frost damage on roots.

Differences in mechanisms of salt tolerance between rice and barley plants

Abstract Mechanisms of salt tolerance were estimated in terms of the ATPase activity in roots, the Na excluding- ability of roots, and the regulation of Na translocation from roots to shoot by comparing Na tolerant plants (barley) and Na sensitive plants (rice) grown at high NaCl concentrations. The results obtained were as follows. 1. As the relative dry weight (dry weight at high NaCl concentration in the medium to the dry weight at 2 mM NaCl concentration in medium) of rice decreased remarkably with the increase of NaCl concentration in the medium compared to that of barley, salt tolerance of barley was higher than that of rice. High salt tolerance of barley was ascribed to the fact that Na translocation from roots to shoot was prevented at high NaCl concentration in the growth medium.2. ATPase activity in roots of rice decreased remarkably with the increase of NaCl concentration (50 to 200 mM NaCl), while that of barley grown at a high NaCl concentration remained high. Since the effect of the NaCl concentration in the reaction solution on the ATPase activity in vitro was negligible, high NaCl concentration in medium may not inhibit directly ATPase but may inhibit indirectly ATPase synthesis or denature membranes, etc.3. ATPase activities in the plasma membrane and tonoplast of barley roots were higher than those of rice when roots were exposed to NaCl concentrations in the range from 0 to 25 mM in the medium.4. When 22Na tracer experiment was conducted over a short period of time, both Na exclusion from roots and Na retranslocation from shoot to roots were higher in rice than in barley, regardless of Na concentration (2 to 150 mM Na) in medium because ATPase activity of the plasma membrane and tonoplast in rice roots remained high under short Na treatment. In rice other factors were involved, such as Na sensitivity of leaf tissues after prolonged exposure. Thus, immediately after the exposure of roots to NaCl, roots of rice plants actively excluded Na from roots to medium, and a large amount of Na was retranslocated from shoots to roots in rice plant compared to barley. However, when rice plants were exposed to high NaCl concentrations for a long period of time, the functions of Na exclusion and Na retranslocation from shoots to roots could not be maintained because the ATPase activity of roots of rice plants decreased due to the high Na concentration in the medium, and the metabolism of leaf tissues was more sensitive to Na in rice than in barley.

Effects of pH and Mineral Nutrition Supply on K +( 86Rb +) Influx and Plasma Membrane ATPase Activity in Roots of Sugar Beets

Sugar beet seedlings ( Beta vulgaris L. cv. Primahill) were cultivated at varying pH and nutrient levels addition rates. Hydrolyzing ATPase activity of root plasma membranes and K + ( 86 Rb + ) flux into roots of intact plants were determined after the different treatments. Relatively high pH (6.5), high concentration of nutrients and a high sodium: potassium (Na: K) ratio in the root medium increased the specific Na + − and (Na + + K + )-activation of the ATPase. In contrast, a low relative addition rate of nutrients and low pH (5.3) enhanced the specific K + -activation. The 2,4-dinitrophenol (DNP)-sensitive (metabolic) influx of K + ( 86 Rb + ) increased > 3 times when the seedlings were raised at pH 5.0, as compared with pH 6.0, and was higher after a relatively low addition rate of nutrients than after a higher rate, or high concentration of nutrients during the cultivation. Thus the specific K + -activation of the ATPase and the K + ( 86 Rb + ) influx were increasing under the same conditions. If K + influx depends on the activity of the H + -ATPase, these results suggest that the activity of the H + -pump increases at low pH and limited supply of nutrients. At high pH and high Na + : K + ratio in the nutrient solution, the increased activation of the ATPase by Na + , and less activation by K + , indicates a larger capacity to extrude Na + than to extrude protons and take up K + .

Changes of some properties of the plasma membrane-enriched fraction of barley roots related to aluminum stress: Membrane-associated ATPase, aluminum and calcium

Abstract A microsomal membrane fraction was prepared from barley roots which were treated with and without 1 mM AICl3. Plasma membrane was dominant in the fraction based on the inhibitor experiment of ATPase activity. ATPase activity of the microsomal membrane fraction decreased after treatment of roots with aluminum. The microsomal membrane fraction was fractionated on a continuous density gradient of sucrose, and the amount of Ca2+ and aluminum associated with the membrane was investigated. The ATPase activity of roots treated with 1 mol m-3 AlCl3 for 5 d decreased to 55.3% of that of the control sample. The amount of Ca2+ associated with the membrane of the Al-treated sample was approximately half as large as that of the control, while substantial binding of Al to the membrane was observed in the sample prepared from the aluminum-treated roots. The K m values for ATP of the fractionated ATPase was 0.45 mol m-3 in both the aluminum-treated and control sample while V max was smaller in the Al-treated sam...