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1.
Physiological and biochemical modifications induced by Fe-deficiency have been studied in cucumber ( Cucumis sativus L. cv. Marketer) roots, a Strategy I plant that initiates a rapid acidification of the medium and an increase in the electric potential difference when grown under Fe-deficiency. Using the aqueous two-phase partitioning method, a membrane fraction which has the plasmalemma characteristics was purified from roots of plants grown in the absence and in the presence of iron. The plasma membrane vesicles prepared from Fe-deficient plants showed an H+ -ATPase activity (EC 3.6.1.35) that is twice that of the non-deficient control. Furthermore, membranes from Fe-deficient plants showed a higher capacity to reduce Fe3+ -chelates. The difference observed in the reductase activity was small with ferricyanide (only 30%) but was much greater with Fe3 -EDTA and Fe3 -citrate (210 and 250%, respectively). NADH was the preferred electron donor for the reduction of Fe3+ compounds. Fe3+ reduction in plasma membrane from cucumber roots seems to occur with utilisation of superoxide anion, since addition of superoxide dismutase (SOD; EC 1.15.1.1) "in vitro" decreased Fe3+ reduction by 60%.
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O2 in controlling the Fe3+ /Fe2+ ratio in the rhizosphere are discussed. 相似文献
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O
2.
John M. Cheeseman 《Physiologia plantarum》1985,64(2):243-246
Models for the regulation of K+ uptake in higher plant roots have become more complex as studies have moved from the level of excised low-salt roots to that of intact plants grown under fully autotrophic conditions. In this paper we suggest that some of the differences between the conditions are qualitative, possibly requiring fundamental changes to the model, rather than simply quantitative.
The uptake of K+ by low-salt roots of Zea mays L. [(A619 x Oh 43) x A632], was independent of Na+ concentration over a wide range. However, independence of Na+ was not the case in plants grown on complete nutrient medium in the light: inclusion of Na+ in the uptake medium enhanced K+ uptake. In the presence of Na+ , K+ uptake rates were similar in whole plants with high root K+ contents to rates in excised or intact, low-salt roots. 相似文献
The uptake of K
3.
Harald Kosegarten Bernd Hoffmann Evan Rroco Franz Grolig Karl-Heinz Glüsenkamp Konrad Mengel 《Physiologia plantarum》2004,122(1):95-106
The relationship between the apoplastic pH in young sunflower roots ( Helianthus annuus L.) and the plasmalemma ferric chelate reductase (FC-R; EC 1.16.1.7) activity in roots was investigated. The hypothesis was tested that a high apoplastic pH depresses FC-R activity, thereby restricting the uptake of Fe2+ into the cytosol. Until recently, little has been known about this relationship, because pH and redox reaction measurements are difficult to perform within the confines of the root apoplast. We recorded the apoplastic pH by means of the fluorescence ratio in conjunction with video microscopy by covalently tagging fluorescein boronic acid to OH groups of the root cell wall. FeIII reduction was measured using a similar approach by tagging ferrozine diboronic acid with OH groups of the cell wall. Ferrozine forms an Fe2+ complex, thus indicating the reduction of ferric iron. In roots bathing in buffered outer solutions of different pH, a high pH sensitivity of apoplastic FeIII reduction was found, with the highest ferric iron reduction rates at an apoplastic pH of 4.9; above an apoplastic pH of 5.3, no reduction was observed. Nitrate in the bathing solution increased the apoplastic pH and hence depressed the FeIII reduction; ammonium had the reverse effect. Nitrate together with HCO3 – , a combination which is typical of calcareous soils, had the strongest depressing effect. From the results, it can be concluded that the main reason for the frequently occurring iron deficiency chlorosis of plants grown on calcareous soils is the inhibition of FeIII reduction in the apoplast, and hence Fe2+ uptake into the cytosol. 相似文献
4.
The uptake of Cd2+ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd2+ uptake approached saturation with a single phase hyperbola. The time course of Cd2+ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q10 of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q10 values were only 1–1.3. It is concluded that Cd2+ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd2+ and for Fe2+ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe2+ , with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd2+ was inhibited. Adsorption and absorption of Cd2+ were strongly inhibited by Ca2+ and by Mg2+ , but were unaffected by Fe2+ . Monovalent ions (Na+ , K+ , Li+ ) also reduced Cd2+ absorption, but to a lesser extent than Ca2+ and Mg2+ . Uptake of Cd+ was reduced at lower pH of the medium. The importance of interfering cations for Cd2+ tolerance of T. aphylla is emphasized. 相似文献
5.
Pb and Cd uptake in rice roots 总被引:9,自引:0,他引:9
Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb2+ and Cd2+ are affected by the presence of K+ , Ca2+ or Mg2+ . K+ had a little effect on uptake or toxicity of Pb2+ and Cd2+ . Ca2+ or Mg2+ blocked both Cd2+ transport into rice roots and Cd2+ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca2+ blocked both Pb2+ transport into the root and Pb2+ toxicity on root growth. The protective effect of Ca2+ on Pb2+ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb2+ toxicity. Mg2+ did not ameliorate the Pb2+ toxicity on root growth as much as Ca2+ did, although it decreased Pb2+ uptake into roots similarly as Ca2+ did. These results suggest that the protective effect of Ca2+ on Pb2+ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb2+ and Cd2+ may compete with divalent cations for transport into roots of rice plants. 相似文献
6.
Yi-Chieh Chang Jian Feng Ma Takashi Iwashita Hideaki Matsumoto 《Physiologia plantarum》1999,106(1):62-68
The effect of Aluminum (Al) on phytosiderophore-mediated solubilization of insoluble Fe and the uptake of phytosiderophore-Fe3+ complex was examined in wheat ( Triticum aestivum L. cv. Atlas 66). Al addition did not affect the Fe solubilization by 2'-deoxymugineic acid (DMA), although Cu addition significantly inhibited the solubilization capacity. Addition of ten times more Al than Fe to the solution of DMA-Fe3+ complex did not decrease the absorption of the DMA-Fe3+ complex at 375 nm. Furthermore, NMR study indicated that Al did not shift the proton chemical shifts of DMA. All these results suggest that Al could not form a complex with the phytosiderophore, and is thereby unlikely to affect the process of phytosiderophore-mediated solubilization of Fe. Exposure of root to Al up to 100 μ M for 3 h did not inhibit the DMA-Fe3+ uptake by the roots, but longer pretreatment (>6 h) inhibited the uptake of the DMA-Fe3+ by more than 50%. Neither the uptake of DMA-Fe3+ nor root elongation was inhibited by 24 h pretreatment with 10 μ M Al, but both uptake and root elongation were inhibited by higher Al (>20 μ M ) pretreatment. These results suggest that Al did not directly block the transport of the phytosiderophore-Fe3+ complex, and that the decreased uptake of the phytosiderophore-Fe3+ complex resulted from the roots being damaged by Al. 相似文献
7.
The K+ (86 Rb) uptake into the roots and the translocation to the shoots of 11-day-old intact wheat seedlings ( Triticum aestivum L. cv. Martonvásári 8) were investigated using plants grown with different K+ supplies. The effects of environmental conditions (darkness, humidity) and of metabolic and transport inhibitors (oligomycin, disalicylidene-propanediamine, 2,4-dinitriphenol, diethylstilbestrol, colchicine) were also studied. Plants with K content of about 0.2 mmol/g dry weight in the root and 0.5 mmol/g dry weight in the shoot (low K status) showed high K+ uptake into the roots and high translocation rates to the shoots. Both transport processes were very low in plants with K content of more than 1.5 and 2.2 mmol/g dry weight in the root and shoot, respectively (high K status).
Darkness and a relative humidity of the air of 100% did not influence K+ uptake by roots, but did inhibit upward translocation and water transport. Inhibition of photosynthesis and treatments with diethylstilbestrol (10−5 mol/dm3 ), as well as with colchicine resulted in inhibition of translocation in plants of low K status, but these inhibitors had little effect on K+ uptake by the roots. Oligomycin, 2,4-dinitrophenol and diethylstilbestrol (10−4 mol/dm3 ), however, inhibited K+ uptake by the roots. In general, K+ transport processes were almost unchanged in plants of high K status. It is concluded that only plants of low K status operating with active K+ transport mechanisms are responsive to environmental factors. In high K+ plants the transport processes are passive and are uncoupled from the metabolic energy flow. 相似文献
Darkness and a relative humidity of the air of 100% did not influence K
8.
Uptake and translocation of calcium in cucumber 总被引:1,自引:0,他引:1
Bengt Bengtsson 《Physiologia plantarum》1982,54(2):107-111
Uptake and translocation of Ca2+ (45 Ca) were compared with water translocation in 12-day old intact plants and excised roots of cucumber ( Cucumis sativus L. var. Cilla), which had been cultivated in nutrient solution. No immediate reduction of Ca2+ uptake was found when water translocation was reduced by excision of the shoot. In the presence of 2,4-dinitrophenol Ca2+ translocation was reduced in the intact plants while water translocation was unchanged. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root. The DNP-sensitive mechanism of Ca2+ uptake was associated with the root and probably represented transport through the endodermis into the stele. 相似文献
9.
Uptake and distribution of calcium, magnesium and potassium in cucumber of different age 总被引:1,自引:0,他引:1
Uptake and distribution of Ca+ , Mg2+ and K2+ were investigated in plants of cucumber ( Cucumis sativus L. var. Cila) which had been cultivated for 12, 19, 32, or 53 days in complete nutrient solution with 1.0 m M Ca2+ , 2.0 m M Mg2+ and 2.0 m M K+ . The + concentration was about the same in roots and shoots, while the Ca2+ and Mg2+ concentrations were low in roots compared to shoots. The K+ concentration decreased with increasing leaf age, while the Ca2+ and Mg2+ concentrations increased, except in older plants with flowers and fruits, where an increased concentration was found in the youngest leaves. This is discussed in connection with increased indoleacetic acid (IAA) synthesis in the shoot. Excision of leaves at different levels from 21-day-old plants, followed by uptake for 24 h from the nutrient solution on days 22 and 23, resulted in no immediate reduction in Ca2+ (45 Ca) uptake. Transport of Ca2+ increased to leaves above and below the excision point and total Ca2+ uptake remained at the same level as for the intact plant. It is suggested that regulation of Ca2+ uptake is primarily achieved in the root while the distribution in the shoot is regulated by the accessability of negative binding sites. 相似文献
10.
Four-week-old sunflower plants ( Helianthus annuus L. cv. Halcón), grown in different nutrient solutions, were used to study the effects of gibberellic acid (GA3 ) on K+ (Rb+ ) uptake by roots or transport to the shoot. Gibberellic acid application to the nutrient solution did not affect the exudation process of excised roots. When GA3 was sprayed on leaves 2 to 6 days before excising the roots, the rate of exudation and the K+ flux increased. When the exudation study was done keeping the roots in a nutrient solution in which Rb+ replaced K+ , the GA3 effects were evident also on Rb+ uptake and transport. In intact plants, GA3 increased the Rb+ transported to the shoot but did not affect Rb+ accumulation in the root. It is suggested that these GA3 effects can be explained if it is assumed that GA3 acts on the transport of ions to the xylem vessels. 相似文献
11.
Shading of maize plants ( Zea mays L. cv. Blizzard) reduced net H+ extrusion by roots and increased K+ release, whereas there was no significant effect on anion efflux in deionized water. With lower light intensity the concentrations of carbohydrates in the roots decreased, but ATP levels and energy charge remained unchanged. Also, shading raised the tissue pH of roots and made the cytoplasmic pH of root cells drop. There was a significant influence of light intensity on H+ uptake by roots from an acidified test solution and CCCP (carbonylcyanide-3-chlorophenylhydrazone)-in-duced H+ uptake was modified by shading.
It is concluded that low light intensity does not limit active H+ release by plasmalemma ATPase activity in the root cells, but that a reduced carbohydrate supply brings about a change in biochemical reactions which alter the membrane permeability for protons. An increased passive reflux of H+ into the cells rather than a reduced H+ ATPase activity explains the decrease of net H+ release by roots of intact maize plants under low light intensity. 相似文献
It is concluded that low light intensity does not limit active H
12.
New insights into the metal specificity of the Pseudomonas aeruginosa pyoverdine–iron uptake pathway
Armelle Braud Françoise Hoegy Karine Jezequel Thierry Lebeau Isabelle J. Schalk 《Environmental microbiology》2009,11(5):1079-1091
Pyoverdine (PvdI) is the major siderophore secreted by Pseudomonas aeruginosa PAOI in order to get access to iron. After being loaded with iron in the extracellular medium, PvdI is transported across the bacterial outer membrane by the transporter, FpvAI. We used the spectral properties of PvdI to show that in addition to Fe3+ , this siderophore also chelates, but with lower efficiencies, all the 16 metals used in our screening. Afterwards, FpvAI at the cell surface binds Ag+ , Al3+ , Cd2+ , Co2+ , Cu2+ , Fe3+ , Ga3+ , Hg2+ , Mn2+ , Ni2+ or Zn2+ in complex with PvdI. We used Inductively Coupled Plasma-Atomic Emission Spectrometry to monitor metal uptake in P. aeruginosa : TonB-dependent uptake, in the presence of PvdI, was only efficient for Fe3+ . Cu2+ , Ga3+ , Mn2+ and Ni2+ were also transported into the cell but with lower uptake rates. The presence of Al3+ , Cu2+ , Ga3+ , Mn2+ , Ni2+ and Zn2+ in the extracellular medium induced PvdI production in P. aeruginosa . All these data allow a better understanding of the behaviour of the PvdI uptake pathway in the presence of metals other than iron: FpvAI at the cell surface has broad metal specificity at the binding stage and it is highly selective for Fe3+ only during the uptake process. 相似文献
13.
The uptake of the auxin type herbicide 2,4-D into rice seedlings ( Oryza sativa L. cv. Dunghan Shali) and its effects on the K+ , NH+ 4 and NO3 ion uptake and the K+ content were investigated at different pH values. A short incubation of the roots in 0.01 m M 2,4-D caused a marked ion uptake inhibition only at low pH. The non-auxin type herbicide benthiocarb did not produce such an inhibitory effect. Lowering of the pH in the external medium led to an increased 2,4-D uptake by the roots. These results can be explained by the increased H+ permeability of the membranes, allowing a more rapid entrance of 2,4-D into the root cells, thereby inhibiting the active ion uptake. Rice roots not subjected to 2,4-D treatment responded to H+ stress with an increased anomalous K+ uptake and a decreased K+ content. With reference to the effects of pH changes on the ion and 2,4-D uptake, possible transport mechanism of NH+ 4 and 2,4-D are briefly discussed. 相似文献
14.
As water and nutrient uptake should be related in the response of plants to salinity, the aim of this paper is to establish whether or not aquaporin functionality is related to H+ -ATPase activity in root cells of pepper ( Capsicum annuum L.) plants. Thus, H+ -ATPase activity was measured in plasma membrane vesicles isolated from roots and aquaporin functionality was measured using a cell pressure probe in intact roots. Salinity was applied as 60 m M NaCl or 60 m M KCl, to determine which ion (Na+ , K+ or Cl− ) is producing the effects. We also investigated whether the effects of both salts were ameliorated by Ca2+ . Similar results were obtained for cell hydraulic conductivity, Lpc , and H+ -ATPase activity, large reductions in the presence at NaCl or KCl and an ameliorative effect of Ca2+ . However, fusicoccin (an activator of H+ -ATPase) did not alter osmotic water permeability of protoplasts isolated from roots. Addition of Hg2+ inhibited both ATPase and aquaporins, but ATPase also contains Hg-binding sites. Therefore, the results indicate that H+ -ATPase and aquaporin activities may not be related in pepper plants. 相似文献
15.
Treeby, M. T. and van Steveninck, R. F. M. 1988. The influence of salinity on phosphate uptake and distribution in lupin roots. - Physiol. Plant. 72: 617–622.
The uptake and distribution of phosphate in lupin ( Lupinus luteus L. cv. Weiko III) roots under moderate salt (NaCl) stress was studied. Vacuolar inorganic phosphate (PJ concentrations in high phosphate plants were decreased by salt, although whole root P| was unaffected. In low phosphate plants, vacuolar Pi was unaffected by salt while whole root Pi was increased. Phosphate uptake was not altered by salt in high phosphate plants, but was depressed in low phosphate plants. These observations lead to the conclusion that in high phosphate plants Pi accumulates in cytoplasm and/or stele, ultimately giving rise to phosphate toxicity in shoots. Increasing phosphate supply had no effect on Na+ accumulation in root cell vacuoles in the epidermis or cortex, but the concentration of Cl− in endodermal vacuoles was lowered. 相似文献
The uptake and distribution of phosphate in lupin ( Lupinus luteus L. cv. Weiko III) roots under moderate salt (NaCl) stress was studied. Vacuolar inorganic phosphate (PJ concentrations in high phosphate plants were decreased by salt, although whole root P| was unaffected. In low phosphate plants, vacuolar P
16.
Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K+ and NO3 − uptake by roots, both uptake of K+ and NO3 − and secretion into the xylem of young sunflower plants ( Helianthus annuus L.) were measured after changes in light intensity.
No close correlation was observed between the uptake of NO3 − and that of K+ ; an increase in light intensity produced a much greater stimulation of NO3 − uptake than of K+ uptake. On the other hand, secretion of NO3 − into the xylem was tightly coupled to that of K+ , and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K2 -malate shuttle on the regulation by the shoot of K+ and NO3 − secretion in the xylem, which is linked to NO3 − uptake, while K+ uptake is independent of this regulation mechanism. 相似文献
No close correlation was observed between the uptake of NO
17.
Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: importance of induced H+ release 总被引:1,自引:0,他引:1
Plants can exhibit Fe-deficiency stress response when they areexposed to Fe-deficiency conditions. The relative importanceof the individual Fe-deficiency stress-response reactions, forexample, increased release of H+ from roots, enhanced root plasmamembrane-bound Fe3+ -reductase activity, and release of reductant,in Fe-deficiency resistance is not understood. To address thisproblem, the Fe-deficiency stress response of two cultivarsof subterranean clover (subclover), Koala (Trifolium brachycalycinumKatzn. and Morley) (Fe-deficiency resistant) and Karridale (T.subterraneum L.) (Fe-deficiency susceptible), were evaluated.The plants were cultured hydroponically at 0 (Fe) and30 (+Fe) µM Fe3+ EDTA conditions. After 6 d Fe treatment,the Fe Koala and Karridale decreased the pH of the nutrientsolution by 1.83 and 0.79 units, respectively, while the +Feplants increased the pH of the nutrient solution. The H+ -releaserate of the Fe Koala determined 7 d after Fe treatmentinitiation was more than three times higher than that of theFe Karridale. The Fe plants had a significantlyenhanced Fe3+ -reduction rate compared with the +Fe plants foreach cultivar, but the resistant cultivar did not exhibit ahigher root Fe3+ -reduction rate than the susceptible cultivarat each Fe treatment. Reductant release from the roots of subcloverwas negligible. These results indicate that Fe-deficiency-inducedH+ release may be the predominant factor influencing Fe-deficiencyresistance in subclover. Key words: Fe-deficiency, Fe3+ reduction, H+ release, stress response, Trifolium 相似文献
18.
Net fluxes of NH4 + and NO3 – along adventitious roots of rice ( Oryza sativa L.) and the primary seminal root of maize ( Zea mays L.) were investigated under nonperturbing conditions using ion-selective microelectrodes. The roots of rice contained a layer of sclerenchymatous fibres on the external side of the cortex, whereas this structure was absent in maize. Net uptake of NH4 + was faster than that of NO3 – at 1 mm behind the apex of both rice and maize roots when these ions were supplied together, each at 0·1 mol m–3 . In rice, NH4 + net uptake declined in the more basal regions, whereas NO3 – net uptake increased to a maximum at 21 mm behind the apex and then it also declined. Similar patterns of net uptake were observed when NH4 + or NO3 – was the sole nitrogen source, although the rates of NO3 – net uptake were faster in the absence of NH4 + . In contrast to rice, rates of NH4 + and NO3 – net uptake in the more basal regions of maize roots were similar to those near the root apex. Hence, the layer of sclerenchymatous fibres may have limited ion absorption in the older regions of rice roots. 相似文献
19.
Efficiency of the first steps of sulfate utilization by maize hybrids in relation to their productivity 总被引:2,自引:0,他引:2
The genetic variability of the efficiency of the first steps of sulfate utilization and its correlation with productivity were evaluated in nine maize hybrids. 35 SO4 2− uptake by excised roots, uptake by intact plant roots, translocation to leaves, and ATP sulfurylase in leaves were taken into account. Uptake rate by roots of intact plants did not show any pulse within 7 to 12 days from emergence, in contrast with the previously observed behaviour of excised roots during root elongation. The uptake rate of intact plants was positively correlated with that of excised roots, but the variability within the nine genotypes tested was less. Productivity was positively correlated with sulfate uptake by both intact plant and excised roots, the level of significance being higher in the first case. Translocation to leaves and ATP sulfurylase activity were not correlated to productivity. Therefore, in the case of sulfate, the grain yield of commonly cultivated maize hybrids appeared to be controlled more by the root uptake step than by the activation and translocation steps. 相似文献
20.
The effects of external K+ , H+ and Ca2+ concentrations on the intracellular K+ concentration, [K+ ]i, and the K+ -ATPase activity in 2-day-old mung bean roots [ Vigna mungo (L.) Hepper] were investigated. [K+ ]i, in mung bean roots was markedly decreased by external K+ or H+ stress and did not recover the initial value even after the stress was removed. This decrease in [K+ ]i, gradually disappeared with the addition of (Ca2+ . Ca2+ may offset the harmful effects of ion stress. Ca2+ seems to have two effects on K+ transport; control of K+ permeability and activation of K+ uptake, although K+ -ATPase activity was inhibited by Ca2+ concentrations higher than 10–4 M. We suggest that Ca2+ activates K+ uptake indirectly through the acidification of the cytoplasm. 相似文献