Phytotoxicity of the fluoride ion and its uptake from solution culture by Avena sativa and Lycopersicon esculentum

Avena sativa (oats) and Lycopersicon esculentum (tomatoes) were grown in dilute nutrient solutions containing varying concentrations of fluoride (F). Shoot and root growth of tomatoes were limited when calculated F ion activities (F^-) were greater than 1473 M in solution. However, F^- activities up to 5130 m had no effect on the dry weights of oat shoots or roots, suggesting that tomatoes are more sensitive to F toxicity. At low F activities in solution (<1684 M) F concentrations in plant shoots increased almost linearly with activity, but then increased rapidly before reaching an upper asymptote. These findings are discussed in relation to plant uptake and toxicity of F. The complexation of Ca with F has been proposed as the mechanism of selectively altering membrane permeability to F, but further studies are required to confirm the role of Ca. Data recalculated from the literature and from this paper also suggest that growth solution ionic strength is positively related to uptake of F^- by plants.     

Role of mycorrhizal infection in the growth and reproduction of wild vs. cultivated plants

Summary We tested the hypothesis that mycorrhizal infection benefits wild plants to a lesser extent than cultivated plants. This hypothesis stems from two observations: (1) mycorrhizal infection improves plant growth primarily by increasing nutrient uptake, and (2) wild plants often possess special adaptations to soil infertility which are less pronounced in modern cultivated plants. In the first experiment, wild (Avena fatua L.) and cultivated (A. sativa L.) oats were grown hydroponically at four different phosphorus levels. Wild oat was less responsive (in shoot dry weight) to increasing phosphorus availability than cultivated oat. In addition, the root: shoot ratio was much more plastic in wild oat (varying from 0.90 in the low phosphorus solution to 0.25 in the high phosphorus solution) than in cultivated oat (varying from 0.44 to 0.17). In the second experiment, mycorrhizal and non-mycorrhizal wild and cultivated oats were grown in a phosphorus-deficient soil. Mycorrhizal infection generally improved the vegetative growth of both wild and cultivated oats. However, infection significantly increased plant lifespan, number of panicles per plant, shoot phosphorus concentration, shoot phosphorus content, duration of flowering, and the mean weight of individual seeds in cultivated oat, while it had a significantly reduced effect, no effect, or a negative effect on these characters for wild oat. Poor positive responsiveness of wild oat in these characters was thus associated with what might be considered to be inherent adaptations to nutrient deficiency: high root: shoot ratio and inherently low growth rate. Infection also increased seed phosphorus content and reproductive allocation.     

Decrease in nitrate uptake and increase in proton release in zinc deficient cotton,sunflower and buckwheat plants

The effect of varied Zn supply on the pH of the nutrient solution and uptake of cations and anions was studied in cotton (Gossypium hirsutum L.), sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants grown under controlled environmental conditions in nutrient solutions with nitrate as source of nitrogen. With the appearance of visual Zn deficiency symtoms, the pH of the nutrient solutions decreased from 6 to about 5 whereas the pH increased to about 7 when the plants were adequately supplied with Zn. In Zn deficient plants the pH decrease was associated with a shift in the cation-anion uptake ratio in favour of cation uptake. Of the major ions, uptake of Ca²⁺ and K⁺ was either not affected or only slightly lowered whereas NO₃ ^- uptake was drastically decreased in Zn deficient plants. Although the Zn nutritional status of plants hardly affected the NO₃ ^- concentrations in the plants, the leakage of NO₃ ^- from roots of Zn deficient plants into a diluted CaCl₂ solution was nearly 10 times higher than that of plants adequately supplied with Zn. In contrast to Zn deficiency, Mn deficiency in cotton plants neither affected NO₃ ^- uptake nor the pH of the nutrient solution.The results indicate that, probably as a consequence of the role of Zn in plasma membrane integrity and nitrogen metabolism, when Zn is deficient in dicotyledonous species net uptake of NO₃ ^- is particularly depressed which in turn results in an increase in cation-anion uptake ratio and a corresponding decrease in external pH. The ecological relevance of this rhizosphere acidification is discussed.     

Heavy-metal ion uptake by plants from nutrient solutions with metal ion,plant species and growth period variations

Summary Rape, cucumber, wheat, oats and tomato were grown for one to two weeks in nutrient solutions with heavy metals added. Of the metal ions tested (Cr³⁺, Cu²⁺, Co²⁺, CrO₄ ^2-, Ni²⁺, Cd²⁺, Pb²⁺, Mn²⁺, Zn²⁺ and Ag⁺), manganese, nickel and lead exhibited the greatest mobility in cucumber plants, which resulted in the highest shoot/root concentration ratio. Silver was not translocated to the shoots of cucumber plants in measurable amounts.When the plants were grown with 1.0, 10 and 100 M cadmium or nickel in the solution, the shoot and root concentration increased 5–10 times if the metal ion concentration of the solution was increased 10 times.The plants showed great differences in cadmium and nickel uptake. In the shoot, the cadmium concentration increased in the order: oats = wheat < cucumber = rape < tomato, and in the root in the order: oats = wheat < cucumber = rape < tomato. The great uptake of cadmium and nickel by tomato is notable and agrees with other reports.The nickel, and especially the cadmium, concentration in roots and shoots increases with the age of the plant.The results are discussed and related to other investigations. The need for research on the uptake mechanisms of non-essential heavy metals is emphasized. re]19750415     

The effect of manganese-oxidizing bacteria and pH on the availability of manganous ions and manganese oxides to oats in nutrient solutions

Summary The uptake of Mn from manganous ions (Mn-ions) and pyrolusite (MnO₂) by three week-old oat plants (Avena sativa L.) grown in nutrient solutions controlled at pH values between 6 and 8, was almost completely inhibited by suspensions of Mn- oxidizing bacteria over a three day uptake period.Grey speck symptoms of Mn deficiency developed in oats grown for 10 days with Mn bacteria in a nutrient solution that had received 1 ppm Mn ions and was controlled at pH 6.3. Rape plants (Brassica napus L.) absorbed appreciable amounts of Mn from treatments similar to those that inhibited Mn uptake by oats.Treatments which decreased or prevented biological oxidation of Mn ions favoured the uptake of Mn by oats from Mn ions, MnO₂ and bacterial Mn-oxide. Acid conditions (pH 5.0) always increased Mn uptake. This was due in part to inhibition of bacterial oxidation and to an increase in the ability of the plants to obtain Mn from Mn oxides.Uptake of Mn is explained on the basis of the rates of two opposing processes; the rate of release of Mn from oxides and the rate of biological oxidation of Mn ions. The results are discussed in relation to the availability of Mn in soils.     

The effect of Nitrogen on the size of spring barley root system as determined by means of its electric capacity

The size of the spring barley root system was studied on the basis of its electric capacity in plants grown in nutrient solutions either lacking or containing nitrogen in the form of nitrate or ammonium. Root electric capacity changed in dependence on nutrition from Day 12 after emergence, when F values increased in the root systems of plants exposed to nitrate and ammonium salts. In plants grown in H₂O, the values of electric capacity statistically significantly decreased on Days 15 to 17, in plants grown in PK solution lacking nitrogen on Day 20. Root electric capacity of plants grown in full nutrient solution gradually increased on Day 18 after emergence. Then a marked increase in root electric capacity values followed with no statistically significant differences between NH₄ ⁺ and NO₃ ^- nutrition. Nitrate nutrition of barley plants only resulted in an increased root to shoot mass ratio.     

Fe chelates from compost microorganisms improve Fe nutrition of soybean and oat

Iron availability to plants is often limited when soil pH is 7 or higher. In C rich, but Fe limiting environments, microorganisms may produce organic chelators that complex Fe and increase its availability to plants. Seedlings of soybean (Glycine max L.) and oat (Avena sativa L.) plants, with Fe-efficient or inefficient uptake mechanisms, were grown in an Fe free nutrient solution at pH 7.5. Experiments (using a complete factorial design) were conducted in which these seedlings were transferred to a fresh nutrient solution and treated with Fe sources (FeCl₃, FeEDDHA, and Fe complexed with chelators produced by compost microorganisms (CCMs) after their enrichment in an Fe free, glucose medium), Fe concentrations (0 and 6.7 M) and antibiotic (0 and 100 mg streptomycin L^-1). Dry weight of soybean plants and Fe uptake were significantly (P 0.05) higher when Fe was supplied as ⁵⁹FeCCM than as⁵⁹ FeCl₃ and similar to when Fe was supplied as⁵⁹ FeEDDHA. Dry weight of the Fe-inefficient Tam 0-312 oat cultivar was also significantly higher when Fe was supplied as FeCCM. Fe uptake by oat, when supplied as ⁵⁹FeCCM, was twice that for⁵⁹ FeEDDHA and ⁵⁹FeCl₃. Chlorophyll concentration in plants supplied with FeCCM and FeEDDHA was significantly greater (P 0.05) than in minus Fe control plants and in FeCl₃ supplied plants. Activities of catalase and peroxidase, measured as indicators of Fe nutrition in soybean and oats, were generally increased when Fe was supplied with FeCCM as compared to the other Fe sources. The experimental conditions in which the CCMs were produced are similar to those in soil after amendment with manures or other readily available organic materials. These CCMs can bind with Fe, even under slightly alkaline conditions, and effectively improve Fe nutrition of soybean and oat.     

Effect of enriched rhizosphere carbon dioxide on nitrate and ammonium uptake in hydroponically grown tomato plants

Previous reports have indicated positive effects of enriched rhizosphere dissolved inorganic carbon on the growth of salinity-stressed tomato (Lycopersicon esculentum L. Mill. cv. F144) plants. In the present work we tested whether a supply of CO₂ enriched air to the roots of hydroponically grown tomato plants had an effect on nitrogen uptake in these plants. Uptake was followed over periods of 6 to 12 hours and measured as the depletion of nitrogen from the nutrient solution aerated with either ambient or CO₂ enriched air. Enriched rhizosphere CO₂ treatments (5000 μmol mol^-1) increased NO₃ ^- uptake up to 30% at pH 5.8 in hydroponically grown tomato plants compared to control treatments aerated with ambient CO₂ (360 μmol mol^-1). Enriched rhizosphere CO₂ treatments had no effect on NH₃ ⁺ uptake. Acetazolamide, an inhibitor of apoplastic carbonic anhydrase, increased NO₃ ^- uptake in ambient rhizosphere CO₂ treatments, but had no effect on NO₃ ^- uptake in enriched rhizosphere CO₂ treatments. Ethoxyzolamide, an inhibitor of both cytoplasmic and extracellular carbonic anhydrase, decreased NO₃ ^- uptake in ambient rhizosphere CO₂ treatments. In contrast, a CO₂ enriched rhizosphere increased NO₃ ^- uptake with ethoxyzolamide, although not to the same extent as in plants without ethoxyzolamide. It is suggested that a supply of enriched CO₂ to the rhizosphere influenced NO₃ ^- uptake through the formation of increased amounts of HCO₃ ^- in the cytosol. This revised version was published online in June 2006 with corrections to the Cover Date.     

NH(4)(+)-stimulated low-K(+) uptake is associated with the induction of H(+) extrusion by the plasma membrane H(+)-ATPase in sorghum roots under K(+) deficiency

The effect of external inorganic nitrogen and K⁺ content on K⁺ uptake from low-K⁺ solutions and plasma membrane (PM) H⁺-ATPase activity of sorghum roots was studied. Plants were grown for 15 days in full-nutrient solutions containing 0.2 or 1.4 mM K⁺ and inorganic nitrogen as NO₃^-, NO₃^-/NH₄⁺ or NH₄⁺ and then starved of K⁺ for 24, 48 and 72 h. NH₄⁺ in full nutrient solution significantly affected the uptake efficiency and accumulation of K⁺, and this effect was less pronounced at the high K⁺ concentration. In contrast, the translocation rate of K⁺ to the shoot was not altered. Depletion assays showed that plants grown with NH₄⁺ more efficiently depleted the external K⁺ and reached higher initial rates of low-K⁺ uptake than plants grown with NO₃^-. One possible influence of K⁺ content of shoot, but not of roots, on K⁺ uptake was evidenced. Enhanced K⁺-uptake capacity was correlated with the induction of H⁺ extrusion by PM H⁺-ATPase. In plants grown in high K⁺ solutions, the increase in the active H⁺ gradient was associated with an increase of the PM H⁺-ATPase protein concentration. In contrast, in plants grown in solutions containing 0.2 mM K⁺, only the initial rate of H⁺-pumping and ATP hydrolysis were affected. Under these conditions, two specific isoforms of PM H⁺-ATPase were detected, independent of the nitrogen source and deficiency period. No change in enzyme activity was observed in NO₃^--grown plants. The results suggest that K⁺ homeostasis in NH₄⁺-grown sorghum plants may be regulated by a high capacity for K⁺ uptake, which is dependent upon the H⁺-pumping activity of PM H⁺-ATPase.     

Uptake and transport of N,P and K in tomato supplied with nettle water and nutrient solution

Water extract of stinging nettle (Urtica dioica) has a growth stimulating effect on plants. This investigation elucidated effects of nettle water on uptake and transport of N, P and K. Tomato plants (Solanum lycopersicum L. cv. Dansk export) were grown in sand culture 6–8 weeks. Plants were supplied with nettle water and nutrient solution was used as a control medium. Uptake and transport of N, P and K⁺ were determined with isotopes (¹⁵N,³²P and⁸⁶Rb⁺ as a tracer for K⁺) and ion-selective electrodes and in exudation experiments. A 15% higher uptake of nitrogen (¹⁵N assay) was found after nettle water treatment compared with the nutrient solution control. The total amount of nitrogen was also higher in plants cultivated with nettle water. Transport of inorganic and organic nitrogen, measured in exudation experiments, was more than 50% higher for plants supplied with nettle water compared with plants supplied with nutrient solution. In contrast, nettle water had no effect on uptake, transport or total amount of phosphorus and potassium in the plants. Experiments in hydroculture showed that nettle water had a strong pH-elevating effect. Uptake of NH ₄ ⁺ was strongly stimulated by nettle water compared with nutrient solution. By holding pH at a constant level during the uptake period for 6 h, the uptake of NH ₄ ⁺ from nettle water was significantly lower when no adjustment of pH was made. Consequently a good deal of the NH ₄ ⁺ uptake enhancement by nettle water could be explained by pH-stimulation. Assays with the uncoupler/inhibitor 2,4-dinitrophenol (DNP) and dichlorophenyl-dimethyl-urea (DCMU) showed that uptake of nitrogen from nettle water was less metabolically-linked than uptake from a corresponding nutrient solution. All together, nettle water seems to stimulate the uptake of nitrogen, but not phosphorus or potassium.     

Speciation analysis of nickel in soil solutions and availability to oat plants

Soil solutions were collected for speciation analysis of nickel from a pot experiment with oats. Oat plants (Avena sativa L.) were grown on 3 soils differing in total amount and origin of nickel (Ni) (Luvisol, LS with 28 mg kg^-1; sludge amended Luvisol, LS+SS with 32 mg kg^-1; Cambisol, CS with 95 mg kg^-1). Results were compared with those for soil solutions obtained from corresponding unplanted pots. Separation methods were used for characterization of size and charge distribution and stability of the Ni species. In addition, short-term experiments were performed on the uptake rates of Ni by oat plants from the different soil solutions as well as from nutrient solutions with increasing concentrations of a synthetic chelator.The Ni concentrations in the soil solutions of unplanted soils increased in the order: LS5000 g mol^-1) was the predominant form, whereas in the other soils the low-molecular-size cationic and chelated Ni species (500–1000 g mol^-1) dominated in the soil solution. In the short-term uptake studies, the uptake rates of Ni from the solutions decreased in the order: nutrient solution > soil solutions, and in the latter in the order: LS>LS+SS>CS, which was inversely related to the concentrations of dissolved organic carbon in the soil solutions.The results demonstrate that Ni availability to plants is not only affected by total concentration of Ni in the soil solution and the rate of replenishment from the solid phase, but also by Ni species, which can differ considerably between soil types.     

Effect of two nutrient solution temperatures on nitrate uptake,nitrate reductase activity,NH4+ concentration and chlorophyll a fluorescence in rose plants

The effect of two nutrient solution temperatures (cold (10 °C) and warm (22 °C)) during two flowering events of rose plants (Rosa × hybrida cv. Grand Gala) were examined by measuring chlorophyll (Chl) a fluorescence, ammonium (NH₄⁺) content and nitrate reductase (NR) activity in four different leaf types, that is, external and internal leaves of bent shoots and lower and upper leaves of flowering stems. Besides, nitrate (NO₃^?) uptake and water absorption, total nitrogen (N) concentration in the plant, dry biomass, and the ratios of shoot/root and thin-white roots/suberized-brown roots were determined. Generally, cold solution increased NO₃^? uptake and thin-white roots production but decreased water uptake, so plants grown at cold solution had to improve their NO₃^? uptake mechanisms to obtain a higher amount of nutrient with less water absorption than plants grown at warm solution. The higher NO₃^? uptake can be related to an increase in NR activity, NH₄⁺ content and total N concentration at cold solution. Nutrient solution temperature also had an effect on the photosynthetic apparatus. In general terms, the effective quantum yield (?_PSII) and the fraction of open PSII reaction centres (q_L) were higher in rose plants grown at cold solution. These effects can be associated to a higher NO₃^? uptake and total N concentration in the plants and were modulated by irradiance throughout all the experiment. Plants could adapt to cold solution by enhancing their metabolism without a decrease in total dry biomass. Nevertheless, the effect of nutrient solution temperature is not simple and also affected by climatic factors.     

Fe isotope fractionation caused by translocation of iron during growth of bean and oat as models of strategy I and II plants

Background

The determination of the plant-induced Fe-isotopic fractionation is a promising tool to better quantify their role in the geochemical Fe cycle and possibly to identify the physiological mechanisms of Fe uptake and translocation in plants. Here we explore the isotope fractionation caused by translocation of Fe during growth of bean and oat as representatives of strategy I and II plants.

Methods

Plants were grown on a nutrient solution supplemented with Fe(III)-EDTA and harvested at three different ages. We used the technique of multi-collector ICP-MS to resolve the small differences in the stable iron isotope compositions of plants.

Results

Total bean plants, regardless of their age, were found to be enriched in the light iron isotopes by ?1.2‰ relative to the growth solution throughout. During growth plants internally redistributed isotopes where young leaves increasingly accumulated the lighter isotopes whereas older leaves and the total roots were simultaneously depleted in light iron isotopes. Oat plants were also enriched in the light iron isotopes but during growth the initial isotope ratio maintained in all organs at all growth stages.

Conclusions

We conclude that isotope fractionation in bean as a representative of strategy I plants is a result of translocation or re-translocation processes. Furthermore we assume that both uptake and translocation of Fe in oat maintains the irons’ ferric state, or that Fe is always bound to high-mass ligands, so that isotope fractionation is virtually absent in these plants. However, in contrast to our previous study in which strategy II plants were grown on soil substrate, oat plants grown on Fe(III)-EDTA contain iron that enriches ⁵⁴Fe by 0.5 permil over ⁵⁶Fe. A possible explanation for the enrichment is the prevalence of a constitutive reductive uptake mechanism of iron in the nutrient solution used which is non-deficient in iron.     

Nutrient Influences on Leaf Photosynthesis: EFFECTS OF NITROGEN, PHOSPHORUS, AND POTASSIUM FOR GOSSYPIUM HIRSUTUM L

The net rate of CO₂ uptake for leaves of Gossypium hirsutum L. was reduced when the plants were grown at low concentrations of NO₃^-, PO₄^2-, or K⁺. The water vapor conductance was relatively constant for all nutrient levels, indicating little effect on stomatal response. Although leaves under nutrient stress tended to be lower in chlorophyll and thinner, the ratio of mesophyll surface area to leaf area did not change appreciably. Thus, the reduction in CO₂ uptake rate at low nutrient levels was due to a decrease in the CO₂ conductance expressed per unit mesophyll cell wall area (g^cell_CO2). The use of g^cell_CO2 and nutrient levels expressed per unit of mesophyll cell wall provides a new means of assessing nutrient effects on CO₂ uptake of leaves.     

Effect of ammonium concentration on growth and nitrogen accumulation by soybean grown in nutrient solution

Soybean (Glycine max (L.) MERR. CV. ‘Amsoy’) plants were grown for 40 days in nutrient solution at various concentrations of ammonium. Maximum yield of dry matter was obtained at a concentration of 715 μM. Further increase in the concentration of ammonium resulted in a reduction in growth due to ammonium toxicity which affected both root and shoot development. The pattern of nitrogen accumulation in tops was consistent with the multiphasic uptake of ammonium and can be represented by 2 phases in the range 1.78 X 10-⁵-3.57 x X 10-³ M of ammonium.     

Kinetics of ammonium and nitrate uptake among wild and cultivated tomatoes

Summary Concentration dependence of net ammonium and nitrate uptake was monitored for a cultivar of tomato, Lycopersicon esculentum, and two accessions of a neotropical wild relative, L. hirsutum. The kinetics of net NH ₄ ⁺ uptake differed among these taxa and were not dependent on the ionic composition of the nutrient solution. The kinetics of net NO ₃ ^- uptake were dependent on the composition of the nutrient solution; the presence of NH ₄ ⁺ or Cl^- enhanced net NO ₃ ^- uptake for the cultivated species and for a highland accession of the wild species. The capacity for net NO ₃ ^- uptake was greater than the capacity for net NH ₄ ⁺ uptake in all three taxa; the proportion of NO ₃ ^- to NH ₄ ⁺ absorbed was much greater for the wild taxa. Our data suggest that NO ₃ ^- may be a more important source of mineral nitrogen than NH ₄ ⁺ for these tropical taxa.     

Simulation study of nutrient uptake by plants from soilless cultures as affected by salinity buildup and transpiration

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis–Menten active mechanisms for K⁺, NO₃ ^–-N, NH₄ ⁺-N, PO₄-P, Ca²⁺, Mg²⁺ and SO₄ ^2-, whose influx parameters are affected by Na and Cl^–, but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations–anions concentrations is balanced by Cl^– to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO₃ ^– and K⁺ uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K⁺ uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.     

Nitrate and ammonium as nitrogen sources for lupins prior to nodulation

Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO₃ ^-, NH₄ ⁺ or NH₄NO₃ with a total nitrogen concentration of 2.8 M m^-3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO₃ ^-, NH₄ ⁺ or NH₄NO₃. However, when NO₃ ^- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ for 30 h, NH₄ ⁺ uptake was generally twice as fast as NO₃ ^- uptake, even for plants grown in the presence of NO₃ ^-. Low rates of NO₃ ^- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO₃ ^-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH₄ ⁺ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH₄ ⁺ was the sole nitrogen source.     

Interactive effect of salt (NaCl) and nitrogen form on growth, water relations and photosynthetic capacity of sunflower (Helianthus annum L.)

The effects of the ammonium (NH₄⁺) and nitrate (NO₃^-) forms of nitrogen and NaCl on the growth, water relations and photosynthesis performance of sunflower (Helianthus annuus L.) were examined under glasshouse conditions. Eight-day-old plants of cv. Hisun 33 were subjected for 21 days to Hoagland's nutrient solution containing 8 mol m^-3N as NH₄⁺or NO₃^-, and salinised with 0, 60, or 120 mol m^-3NaCl. Fresh weights of shoots and roots, and leaf area of NO₃^-supplied non-salinised plants were significantly greater than those of NH₄⁺-supplied non-salinised plants. But addition of NaCl to the rooting medium of these plants had more inhibitory effect on the growth of NO₃^--supplied plants than on NH₄⁺-supplied plants. Both leaf water and osmotic potentials of plants grown with NH₄⁺were lower than those of plants given NO₃^-under both non-saline and saline conditions. Chlorophylls a and b concentrations were higher in plants grown with NH₄⁺than N0₃^--supplied plants at the lower two levels of salinisation. The rate of photosynthesis in plants was considerably higher in non-salinised plants grown with NO₃^-than with NH₄⁺, but with increase in salinisation the photosynthesis rate decreased in NO₃^--supplied plants, but not in those given NH₄⁺. The rate of transpiration was increased significantly by salinisation in NO₃^--supplied plants, but not consistently so in NH₄⁺-supplied plants. The stomatal conductances were much higher in plants given NO₃^-than with NH₄⁺when grown under non-saline conditions, but not when salinised. As a consequence, water-use efficiency in NO₃^--supplied control plants was better than in NH₄⁺-supplied under non-saline conditions, but worse under saline conditions. The different forms of nitrogen and the addition of NaCl to the growing medium did not affect the relative intercellular concentrations of CO₂ (C_i/C_a). Overall, the NH₄⁺form of nitrogen inhibited the growth of sunflowers under non-saline conditions, but NO₃^-and NaCl interacted to inhibit growth more than did NH₄⁺under saline conditions.     

Silver uptake, distribution, and effect on calcium, phosphorus, and sulfur uptake

Bean, corn, and tomato plants were grown in a nutrient solution labeled with ³²P, ⁴⁵Ca, or ³⁵S and varying concentrations of AgNO₃. Following a 6-hour treatment period, plants were harvested and analyzed. A low Ag⁺ concentration (50 nanomolar) inhibited the shoot uptake of the ions investigated. In the roots, Ca uptake increased whereas P and S uptake decreased.