Péétration et migration d'éléments minéraux appliqués sur les feuilles en présence de diméthylsulfoxyde

The aim of this work was to determine the effect of DMSO on the uptake and translocation of potassium and phosphorus applied on corn and bean leaves. Radioactive isotopes ⁴²K and ³²P were used in most of the experiments. The results obtained reveal that DMSO (0.5% and above) increases the penetration of potassium applied as nitrate or chloride, but seems to have no effect on the penetration of ³²P when applied as different phosphates.     

Effect of primary leaves on 59Fe uptake by roots and 59Fe distribution in the shoot of iron sufficient and iron deficient bean (Phaseolus vulgaris L.) plants

A study has been made on the effect of primary leaves on iron (Fe) distribution in the shoot. Bean (Phaseolus vulgaris L.) seedlings were precultured in nutrient solution with 8×10^-5 M FeEDTA for 4 days, and then grown further with either 8×10^-5 M FeEDTA (+Fe) or without Fe supply (-Fe) for another 5 days. Thereafter, both +Fe and -Fe plants were treated in three different ways: undisturbed; one primary leaf removed; or one primary leaf shaded, starting two hours before supply ⁵⁹FeEDTA to the roots. The +Fe plants were supplied with 8×10^-5 M ⁵⁹FeEDTA, and the -Fe plants with only 1×10^-6 M ⁵⁹FeEDTA. After 1 to 8 hour uptake periods, plants were harvested and ⁵⁹Fe in different organs was determined. Removal or shading of one primary leaf did not affect ⁵⁹Fe uptake by roots and ⁵⁹Fe translocation to the shoot in +Fe plants. In the -Fe plants, however, removal of one primary leaf decreased ⁵⁹Fe uptake by roots, whereas shading of one primary leaf had no effect on ⁵⁹Fe uptake but slightly enhanced ⁵⁹Fe translocation from roots to the shoot. The quantity of ⁵⁹Fe in primary leaves was positively correlated with quantity of ⁵⁹Fe in the stem in the -Fepplants, but not in the +Fe plants. In both, the +Fe and -Fe plants, the quantity of ⁵⁹Fe in the shoot apex was positively correlated with ⁵⁹Fe in primary leaves. The results suggest that irrespective of the Fe nutritional status of plants, the source of Fe for the shoot apex is Fe retranslocated from primary leaves.     

Action du diméthylsulfoxyde sur l'absorption du 42K et du glucose-14C (U) par des disques foliaires de Zea mays et Pelargonium zonale

⁴²K and ¹⁴C (U)-glucose uptake by foliar discs of maize (Zea mays L.) and pelargonium (Pelargonium zonale L.) is inhibited by dimethyl sulfoxide (DMSO) at concentrations of 5 and 10%. This effect increases with the duration of the absorption and appears with varied concentrations in K or glucose. In most cases, this inhibitory effect is less with aged discs than with freshly cut discs. Besides, the DMSO (10%) enhances the exsorption of ⁴²K by foliar discs of maize. The effects of DMSO and two osmotic agents, mannitol and polyethylene glycol 1000, on the uptake and water content of discs are compared. It seems that the effect of DMSO on the uptake is not only an osmotic effect. It may also be related to other actions of this substance in affecting an active uptake.     

Evidence for root Fe nutrition in Hydrilla verticillata Royle

Summary The uptake of Fe by roots and apical leaves of the submersed aquatic plant Hydrilla verticillata Royle was studied using ⁵⁹FeEDTA. ⁵⁹FeEDTA was absorbed by both roots and apical leaves, and translocated to the other parts of the plant. Approximately 3% of the total ⁵⁹FeEDTA absorbed by the roots over a period of 60 h was translocated to the leaves. Downward translocation of ⁵⁹FeEDTA from the apical portion of the plant to the lower leaves was approximately 21% of the amount absorbed.Published as Journal Series No 333 of the Florida Agricultural Experiment Station.     

Uptake of ionic 55Fe by mouse peritoneal macrophages in vitro.

Mouse peritoneal macrophages were maintained in vitro up to 3 days and exposed to radiolabelled ⁵⁵Fe in the form of ferrous citrate, ferrous sulfate, and ferric chloride in concentrations of 3–5 γ Fe/ml. The divalent iron compounds were taken up 10–40 times more extensively per weight of iron than the trivalent iron compounds. The net uptake of ferrous citrate was linear during the first day and thereafter increased at a slower rate. Macrophages in culture for 1 week showed one-third the average uptake of freshly cultured cells during comparable periods of exposure to ferrous citrate. The iron taken up was used in the synthesis of mouse ferritin. Uptake of ferrous citrate was influenced by serum concentration in the tissue culture medium, temperature, pinocytosis and phagocytosis of both latex particles and heated rat erythrocytes. Uptake of ferrous citrate was enhanced by exposure to either sodium fluoride (5×10^?3 M), or 2,4-dinitrophenol (1×10^?5 M), but was not affected by cyanide, azide, or cycloheximide. The effect of sodium fluoride was not demonstrated when ferrous sulfate was substituted for ferrous citrate. The results reported here suggest that the ability of macrophages to take up ferrous citrate is good in freshly explanted cultures, is a temperature-dependent process, is suppressed by pinocytosis and phagocytosis, and paradoxically enhanced by certain metabolic inhibitors.     

Uptake of ionic Fe by mouse peritoneal macrophages in vitro

Mouse peritoneal macrophages were maintained in vitro up to 3 days and exposed to radiolabelled ⁵⁵Fe in the form of ferrous citrate, ferrous sulfate, and ferric chloride in concentrations of 3–5 γ Fe/ml. The divalent iron compounds were taken up 10–40 times more extensively per weight of iron than the trivalent iron compounds. The net uptake of ferrous citrate was linear during the first day and thereafter increased at a slower rate. Macrophages in culture for 1 week showed one-third the average uptake of freshly cultured cells during comparable periods of exposure to ferrous citrate. The iron taken up was used in the synthesis of mouse ferritin. Uptake of ferrous citrate was influenced by serum concentration in the tissue culture medium, temperature, pinocytosis and phagocytosis of both latex particles and heated rat erythrocytes. Uptake of ferrous citrate was enhanced by exposure to either sodium fluoride (5×10⁻³ M), or 2,4-dinitrophenol (1×10⁻⁵ M), but was not affected by cyanide, azide, or cycloheximide. The effect of sodium fluoride was not demonstrated when ferrous sulfate was substituted for ferrous citrate. The results reported here suggest that the ability of macrophages to take up ferrous citrate is good in freshly explanted cultures, is a temperature-dependent process, is suppressed by pinocytosis and phagocytosis, and paradoxically enhanced by certain metabolic inhibitors.     

An Exogenous Source of Nitric Oxide Modulates Iron Nutritional Status in Peanut Seedlings (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.)

Iron (Fe) deficiency chlorosis is a common and severe nutritional deficiency in plants, and nitric oxide (NO) is an important signaling molecule in regulating Fe homeostasis in plants. We studied the effect of sodium nitroprusside (SNP, an NO donor) on Fe uptake, translocation, storage, and activation in a greenhouse. The concentrations of active Fe, total Fe, and the ratio of active Fe to total Fe, the activities of key enzymes, and chlorophyll concentration were determined, and resistance to oxidative stress and mineral element distribution in peanut plants grown in Fe sufficiency and Fe deficiency (an absence of Fe and low level of Fe concentration) conditions were also investigated. The results showed that NO significantly increased the concentration of active Fe and the ratio of active Fe to total Fe in Fe-deficient plants, and increased active Fe concentration in leaves and stems of Fe-sufficient plants. NO application also increased Fe translocation from roots to the shoots and the accumulation of Fe in cell organelles and the soluble fraction in leaves, especially in the low-level Fe concentration condition, thus increased available Fe and chlorophyll concentration in leaves of Fe-deficient plants. The activities of key enzymes were regulated by NO, which effectively mitigated oxidative damages by enhancing the activities of antioxidant enzymes (SOD, POD, CAT), increasing H⁺-ATPase and Ca²⁺-ATPase activities to balance the ion (Fe, Ca, Mg and Zn) uptake and distribution in Fe-deficient plants. However, NO application had no obvious effect on these variables in Fe-sufficient plants. These results indicated that NO application can improve Fe uptake, translocation, and activation of related enzymes in Fe-deficient plants, thus mitigating the adverse effect of Fe deficiency.     

Influence of <Emphasis Type="Italic">Methylobacterium</Emphasis> on iron translocation in plants

Iron metabolism in plants is essential to maintain optimal growth and iron nutrition is dependent on uptake of iron from the environment and movement of iron in the plant tissues. We have examined the translocation of iron in plant leaves following foliar application of FeEDTA to Vicia faba and Zea mays. Using radiolabeled iron, we observed that iron translocation is stimulated by products of Methylobacterium mesophylicum and by the cytokinin, kinetin. When cytokinins were applied to leaves along with ⁵⁵FeEDTA, the rate of iron translocation was greater than in controls without cytokinin addition. Since recent studies indicate that M. mesophylicum is widely distributed in the environment as a pyllospheric bacterium, this organism may have an important role in enhancing translocation of nutrients in plant leaves.     

Iron availability in plant tissues-iron chlorosis on calcareous soils

The article describes factors and processes which lead to Fe chlorosis (lime chlorosis) in plants grown on calcareous soils. Such soils may contain high HCO₃ ^- concentrations in their soil solution, they are characterized by a high pH, and they rather tend to accumulate nitrate than ammonium because due to the high pH level ammonium nitrogen is rapidly nitrified and/or even may escape in form of volatile NH₃. Hence in these soils plant roots may be exposed to high nitrate and high bicarbonate concentrations. Both anion species are involved in the induction of Fe chlorosis.Physiological processes involved in Fe chlorosis occur in the roots and in the leaves. Even on calcareous soils and even in plants with chlorosis the Fe concentration in the roots is several times higher than the Fe concentration in the leaves. This shows that the Fe availability in the soil is not the critical process leading to chlorosis but rather the Fe uptake from the root apoplast into the cytosol of root cells. This situation applies to dicots as well as to monocots. Iron transport across the plasmamembrane is initiated by Fe^III reduction brought about by a plasmalemma located Fe^III reductase. Its activity is pH dependent and at alkaline pH supposed to be much depressed. Bicarbonate present in the root apoplast will neutralize the protons pumped out of the cytosol and together with nitrate which is taken up by a H⁺/nitrate cotransport high pH levels are provided which hamper or even block the Fe^III reduction.Frequently chlorotic leaves have higher Fe concentrations than green ones which phenomenon shows that chlorosis on calcareous soils is not only related to Fe uptake by roots and Fe translocation from the roots to the upper plant parts but also dependent on the efficiency of Fe in the leaves. It is hypothesized that also in the leaves Fe^III reduction and Fe uptake from the apoplast into the cytosol is affected by nitrate and bicarbonate in an analogous way as this is the case in the roots. This assumption was confirmed by the highly significant negative correlation between the leaf apoplast pH and the degree of iron chlorosis measured as leaf chlorophyll concentration. Depressing leaf apoplast pH by simply spraying chlorotic leaves with an acid led to a regreening of the leaves.     

Molybdenum and iron as constituents of the enzymes of the nitrate reducing system from chlorella

By adding radioactive ⁹⁹Mo (as molybdate) and ⁵⁹Fe (as ferrous ion) to a culture of Chlorella cells at the moment derepression of the enzymes of the nitrate reducing system was initiated as a consequence of the removal of ammonia from the medium, it could be unequivocally shown that the two metals were incorporated into nitrate reductase and nitrite reductase respectively, remaining associated with the enzymes during purification. After a mild heat treatment of nitrate reductase, exogenous molybdate could be made to interact with the enzyme and to function as electron donor after its chemical reduction with hydrosulfite.     

Role of potassium and malate in nitrate uptake and translocation by wheat seedlings

Wheat seedlings (Triticum vulgare) treated with 1 mm KNO₃ or NaNO₃, in the presence of 0.2 mm CaSO₄, were compared during a 48-hour period with respect to nitrate uptake, translocation, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlings treated with KNO₃ absorbed and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO₃. Within seedlings of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO₃-treated seedlings had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO₃-treated seedlings. NADP-malic enzyme levels increased only slightly in leaves and roots of both KNO₃- and NaNO₃-treated seedlings. The effects of K⁺ and Na⁺ on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phosphoenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO₃ treatment, and increased only slightly in the KCl control.     

Characterization of siderophore-mediated iron transport inGeotrichum candidum,a non-siderophore producer

Summary Geotrichum candidum is capable of utilizing iron from hydroxamate siderophores of different structural classes. The relative rates of iron transport for ferrichrome, ferrichrysin, ferrioxamine B, fusigen, ferrichrome A, rhodotorulic acid, coprogen B, dimerium acid and ferrirhodin were 100%, 98%, 74%, 59%, 49%, 35%, 24%, 12% and 11% respectively. Ferrichrome, ferrichrysine and ferrichrome A inhibited [⁵⁹Fe]ferrioxamine-B-mediated iron transport by 71%, 68% and 28% respectively when added at equimolar concentrations to the radioactive complex. The inhibitory mechanism of [⁵⁹Fe]ferrioxamine B uptake by ferrichrome was non-competitive (K _i 2.4 M), suggesting that the two siderophores do not share a common transport system. Uptake of [⁵⁹Fe]ferrichrome, [⁵⁹Fe]rhodotorulic acid and [⁵⁹Fe]fusigen was unaffected by competition with the other two siderophores or with ferrioxamine B. Thus,G. candidum may possess independent transport systems for siderophores of different structural classes. The uptake rates of [¹⁴C]ferrioxamine B and⁶⁷Ga-desferrioxamine B were 30% and 60% respectively, as compared to [⁵⁹Fe]ferrioxamine B. The specific ferrous chelates, dipyridyl and ferrozine at 6 mM, caused 65% and 35% inhibition of [⁵⁹Fe]ferrioxamine uptake. From these results we conclude that, although about 70% of the iron is apparently removed from the complex by reduction prior to being transported across the cellular membrane, a significant portion of the chelated ligand may enter the cell intact. The former and latter mechanisms seem not to be mutually exclusive.     

Effects of NaCl salinity on 15N-nitrate fluxes and specific root length in the halophyte Plantago maritima L.

The effect of salinity on nitrate influx, efflux, nitrate net uptake rate and net nitrogen translocation to the shoot was assessed in a ¹⁵N steady state labelling experiment in the halophyte Plantago maritima L. raised for 14 days on solution supplied with 50, 100 and 200 mol m^–3 sodium chloride or without sodium chloride. Additionally, salinity induced changes in root morphology were determined. Specific root length increased upon exposure to elevated sodium chloride concentrations due to variations in biomass allocation and length growth of the tap root. Changes in root morphology, however, had a minor effect on nitrate fluxes when expressed on a root fresh weight basis. The decreased rate of nitrate net uptake in plants grown on elevated levels of sodium chloride was almost entirely due to a decrease in nitrate influx. Expressed as a proportion of influx, nitrate efflux remained unchanged and was even lower at the highest salinity level. At all sodium chloride concentrations applied the initial rate of nitrogen net translocation to the shoot decreased relative to the rate of nitrate net uptake. It is concluded that under steady state conditions the negative effect of sodium chloride on the rate of nitrate net uptake at non growth-limiting salinity levels was due to the interaction between sodium chloride and nitrate transporters in the root plasma membrane and/or processes mediating the translocation of nitrogen compounds, possibly nitrate, to the shoot.     

Time-course of Nitrate Uptake and Nitrate Reductase Activity in Nitrogen-depleted Dwarf Bean

The rate of nitrate uptake by N-depleted French dwarf bean (Phaseolus vulgaris L. cv. Witte Krombek) increased steadily during the first 6 h after addition of NO₃ -After this initial phase the rale remained constant for many hours. Detached root systems showed the same time-course of uptake as roots of intact plants. In vivo nitrate reductase activity (NRA) was assayed with or without exogenous NO₃^- in the incubation medium and the result ing activities were denoted potential and actual level, respectively. In roots the difference between actual and potential NRA disappeared within 15 min after addition of nitrate, and NRA increased for about 15 h. Both potential and actual NRA were initially very low. In leaves, however, potential NRA was initially very high and was not affected by ambient nitrate (0.1–5 mol m^-3) for about 10 h. Actual and potential leaf NRA became equal after the same period of time. In the course of nitrate nutrition, the two nitrate reductase activities in leaves were differentially inhibited by cycloheximide (3.6 mmol m^-3) and tungstate (1 mol m^-3). We suggest that initial potential NRA reflects the activity of pre-existing enzyme, whereas actual NRA depends on enzyme assembly during NO₃^- supply. Apparent induction of nitrate uptake and most (85%) of the actual in vivo NRA occurred in the root system during the first 6 h of nitrate utilization by dwarf bean.     

Reduction and transport of Fe from siderophores

Soils contain siderophores produced by bacteria and fungi; however, the role of siderophores in Fe nutrition of plants is uncertain. The Strategy I plant cucumber (Cucumis sativus L.) was used in an investigation of ferric chelate reduction activity and uptake and transport of Fe from ferric hydroxyethylethylenetriacetic acid (FeHEDTA) and ferric N,N–di–(2–hydroxybenzoyl)–ethylenediamine– N,N-diacetic acid (FeHBED) and the hydroxamate siderophores, ferric rhodotorulic acid (FeRA) and ferric ferrioxime B (FeFOB). Cucumber seedlings were grown in a hydroponic medium without Fe or supplied with 10 M FeHEDTA. Iron-deficient cucumber roots readily reduced FeHEDTA, while Fe-sufficient roots had low levels of ferric chelate reduction activity. The siderophore FeRA was reduced by Fe-deficient roots at 8% of the rate of FeHEDTA, while FeFOB was not reduced. The highly stable synthetic chelate FeHBED was reduced at 16% the rate of FeHEDTA. Fe transport to shoots by Fe-deficient seedlings from the slowly reducible complexes ⁵⁹FeRA and ⁵⁹FeHBED was, respectively, 74% and 73% of that transported from ⁵⁹FeHEDTA. The ferrous complexing agent, bathophenanthrolinedisulfonic acid (BPDS), had a strong inhibitory effect on uptake and transport of Fe from ⁵⁹FeHEDTA or ⁵⁹FeRA into shoots. An average of 11% as much Fe was transported to shoots of Fe-deficient seedlings from ⁵⁹FeFOB as from ⁵⁹FeHEDTA. Neither the Fe nutritional status of the seedlings nor the presence of BPDS influenced the uptake and transport of Fe from ⁵⁹FeFOB. It is concluded that cucumber roots may take up substantial amounts of Fe from FeRA and FeHBED following reduction, while small amounts of Fe may be taken up from FeFOB by a mechanism not involving reduction of the ferric siderophore at the root surface.     

EGTA对Cd胁迫下蓖麻Cd积累和营养元素吸收的影响

以‘淄蓖麻5号’蓖麻品种为材料,通过盆栽试验研究了重度Cd土壤污染（100 mg·kg^-1）条件下,不同浓度（0、0.5、1.0、2.0 mmol·kg^-1）外源螯合剂——乙二醇双(2-氨基乙基醚)四乙酸(EGTA)对蓖麻植株生长、Cd积累和营养元素吸收的影响,探讨外源螯合剂调控Cd污染土壤上植物生长和修复效应。结果显示：（1）在Cd胁迫下,土壤中外源添加0.5~2.0 mmol·kg^-1EGTA使蓖麻根系鲜、干重比不添加EGTA对照不同程度降低,但植株总干重没有受到显著影响。（2）外源EGTA能有效促进Cd从蓖麻根部向地上部的转移,2.0 mmol·kg^-1的EGTA处理使蓖麻叶片Cd 含量显著增加了41.34倍;与不添加EGTA对照相比,外源EGTA处理蓖麻叶片中Cd积累量随添加EGTA的浓度增加而显著大幅度增加14.0~45.6倍,占相应植株总积累量的36.89%~58.63%,而茎中Cd积累量增加幅度较小,根中Cd积累量则显著降低。（3）Cd胁迫条件下,外源EGTA对蓖麻各器官矿质元素含量的影响不一,EGTA促进K向蓖麻地上部的转运,同时抑制Mg向植株地上部转运;随土壤添加的EGTA浓度提高,蓖麻植株对Ca吸收表现为低促高抑,叶片Zn含量和植株Cu含量逐渐增加,叶片和根系Fe含量及植株各器官Mn含量显著增加。与无Cd胁迫对照相比,EGTA在提高植株Cd积累的同时,降低了根系对K的吸收。研究表明,Cd胁迫显著抑制了蓖麻植株的生长,适宜浓度的外源EGTA对Cd的这种抑制有显著的缓解作用;外源EGTA改变了Cd在蓖麻根、茎、叶中的积累分布情况,提高了Cd从根系向地上部,尤其是向叶片的转移能力,从而强化了蓖麻对Cd污染土壤的修复效率;在采用EGTA强化植物修复Cd污染土壤时,应适量增施K肥以保证植株的正常生理代谢。     

Metal-ion susceptibility of oral bacterial species

Aims: This study aimed to evaluate the effect of lead (Pb) on growth of bacterial species related to dental diseases in vitro. Methods and Results: The effects of lead acetate on representative species of the oral flora were examined at 0·1–10 mmol l^?1 and compared with the effect of silver nitrate and ferrous sulfate. The minimal inhibitory concentration of lead acetate was between 0·15 and 5 mmol l^?1 for the bacterial strains tested. The minimal bactericidal concentration of lead acetate for most oral species was detected in the range of 5–10 mmol l^?1. Silver nitrate at a concentration of 1·25 mmol l^?1 was sufficient to exhibit antibacterial activity against almost all bacteria tested. Ferrous sulfate had the lowest effect. Conclusions: The study indicated a general antimicrobial effect of lead on oral bacterial species in the range of 0·15–10 mmol l^?1. The toxicity of silver nitrate was the highest, whereas that of ferrous sulfate was the lowest. Gram‐positive species had a tendency to be less susceptible for metals than Gram‐negatives. Significance and Impact of the Study: The study shows that it is possible that microbiological changes may occur in the dental plaque in children because of toxic exposure of environmental lead.     

Microelectrode and 133Cs nuclear magnetic resonance evidence for variable cytosolic and cytoplasmic nitrate pools in maize root tips

The effect of nitrate uptake on the subcellular distribution of tissue nitrate in 2–5 mm maize root tips was investigated by two complementary methods. First a novel in vivo analysis using ¹³³Cs nuclear magnetic resonance (NMR) was used to demonstrate changes in the cytoplasmic and vacuolar pools during caesium nitrate uptake. This method depended on interpreting the nitrate-induced changes in the positions of the cytoplasmic and vacuolar caesium signals. The assignment of the signals was confirmed by using in vivo³⁹K NMR to observe the displacement of cytoplasmic potassium into the vacuole during caesium uptake, and in vivo¹³³Cs NMR to observe the displacement of cytoplasmic caesium into the vacuole during potassium uptake. Secondly nitrate-selective microelectrodes were used to quantify the change in the cytosolic nitrate activity that occurred in the outermost cells of root tips under the same conditions. Both methods showed that the detected nitrate pool increased over a period of 8–10 h in the presence of 10 m m nitrate and it is concluded that the data provide support for the view that homeostasis in the cytosolic and cytoplasmic nitrate pools is not necessarily an invariant characteristic of root tips.