Rhizosphere salinity and phytoalexin accumulation in soybean

Summary Rhizosphere salinity decreased the capacity of soybean to accumulate a pterocarpanoid phytoalexin (glyceollin) in the stem in response toPhytophthora megasperma var.sojae. Rapid (48h) accumulation was depressed by NaCl, Na₂SO₄, CaCl₂ and MgSO₄ applications. Time-course accumulations was slowed by applications. Time-course accumulation was slowed by application of 0.131M NaCl. Glyceollin accumulation was also reduced in plants subjected to a period of high salinity stress (0.177M NaCl, 72 h) after a period of nonsalinized growth. Calcium chloride completely suppressed glyceollin accumulation in normally-resistant plants but no susceptibility to the fungus was observed.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

Effects of temperature and CO2 enrichment on kinetic properties of NADP+-malate dehydrogenase in two ecotypes of Barnyard grass (Echinochloa crus-galli (L.) Beauv.) from contrasting climates

Summary The apparent energy of activation (E _a), Michaelis-Menten constant (K _mfor oxaloacetate), V _max/K _mratios and specific activities of NADP⁺-malate dehydrogenase (NADP⁺-MDH; EC 1.1.1.82) were analyzed in plants of Barnyard grass from Québec (QUE) and Mississippi (MISS) acclimated to two thermoperiods 28/22°C, 21/15°C, and grown under two CO₂ concentrations, 350 l l^-1 and 675 l l^-1. E _avalues of NADP⁺-MDH extracted from QUE plants were significantly lower than those of MISS plants. K _mvalues and V _max/K _mratios of the enzyme from both ecotypes were similar over the range of 10–30°C but reduced V _max/K _mratios were found for the enzyme of QUE plants at 30 and 40°C assays. MISS plants had higher enzyme activities when measured on a chlorophyll basis but this trend was reversed when activities were expressed per fresh weight leaf or per leaf surface area. Activities were significantly higher in plants of both populations acclimated to 22/28°C. CO₂ enrichment did not modify appreciably the catalytic properties of NADP⁺-MDH and did not have a compensatory effect upon catalysis or enzyme activity under cool acclimatory conditions. NADP⁺-MDH activities were always in excess of the amount required to support observed rates of CO₂ assimilation and these two parameters were significantly correlated. The enhanced photosynthetic performance of QUE plants under cold temperature conditions, as compared to that of MISS plants, cannot be attributed to kinetic differences of NADP⁺-malate dehydrogenase among these ecotypes.     

A Salt-Tolerant Cultivar of Wheat Maintains Photosynthetic Activity by Suppressing Sodium Uptake

The effects of NaCl treatment on the photosynthetic machinery in wheat (Triticum aestivum L.) cultivars differing in salt tolerance were investigated by comparison with iso-osmotic PEG treatment. Both cultivars similarly reduced the photosystem 2 (PS2) energy conversion efficiency (_PS2) rapidly when plants were exposed to a 100 mM NaCl solution, though no decline was detected under the iso-osmotic PEG treatment. There was no correlation between the reduction of the leaf relative water content (RWC) and the _PS2 in the two iso-osmotic stress treatments. In contrast, a decline of _PS2 along with the increase of the leaf sodium content above 4 % dry matter was detected under the NaCl treatment, while no such correlation was detected with other cations. The recovery of _PS2 after photoinhibitory irradiation was repressed by the NaCl treatment as the increase of the duration of the treatment. Norin 61 subjected to the 100 mM NaCl treatment for 10 d showed a decline of the _PS2 after 1 h moderate irradiation of 400 mol m^–2 s^–1 PPFD. Thus the concentrated Na⁺ within a leaf under salinity treatments may decrease the stability of PS2 functions and lead to photochemical inactivation.     

Differences in calcium efficiency between cowpea (Vigna unguiculata (L.) Walp.) cultivars

The cowpea (Vigna unguiculata (L.) Walp.) cultivars TVu 354 and Solojo were grown in solution culture at 10 to 1000 M Ca supply. The Ca supply did not vary by more than 10% during the experiment. The pH value was kept constant within 0.1 units at 4.0 by automatic titration. The cultivar TVu 354 proved to be much more Ca-efficient than Solojo. At 10 M Ca supply Solojo died, whereas TVu 354 was hardly affected in dry matter production. The differences in Ca efficiency were independent of the P supply. They could not be explained by differences in Ca uptake or Ca concentrations in the plant tissue. Short-term studies using ⁴⁵Ca, both in the dark and in the light, indicated better transport of Ca from the roots to the shoots and within the shoots to the younger leaves in the Ca-efficient cultivar TVu 354. However, the main reason for the differences between the cultivars in sensitivity to low Ca supply were differences in the Ca requirement of the plant tissue to maintain tissue organization and function. Sequential fractionation of the freeze-dried leaf tissue with hot water, 0.5 M NaCl, 1 M CH₃COOH, and 2 M HCl did not reveal cultivar differences in Ca binding state. The results clearly show that considerable genetic potential in tolerance to low Ca supply exists in cowpea. However, a better understanding of the physiological/biochemical reasons for low internal Ca requirement is needed.     

Copper-binding proteins and copper tolerance in Pisam sativum L.

The effect of high nutrient levels of copper on the low-molecular-weight copper-proteins of leaves from plants of two cultivars of Pisum sativum L., with different sensitivity to copper, was investigated. Gel-filtration chromatography of leaf extracts from Cu-tolerant and Cu-sensitive plants grown with 1 M Cu(II), showed the presence of only two copper peaks (I and II), but growth of plants with 240 M Cu(II) induced two additional copper fractions (III and IV). Fractions II and III were purified by solvent extraction, gel-filtration and ion-exchange chromatography, and their molecular weights, subunit sizes, absorption spectra, metalprotein stoichiometry and amino-acid contents were determined. Fraction II was a polypeptide of M_r 15000 composed of a single chain. The purification of fraction III produced a copper-containing fraction (III-1) of M_r 3700, and a copper-protein (III-2) with an M_r, by sodium dodecyl sulfate-urea-polyacrylamide gel electrophoresis, of 66000. The metal contents of fractions III-1 and III-2 were higher in Cu-tolerant than in Cu-sensitive plants. On the basis of amino-acid analyses, fraction III-1 appeared to be complexes of Cu(II)-poly-isoleucine and Cu(II)-poly-leucine. The results rule out the existence, in pea leaves, of any protein similar to either animal metallothioneins or to any of the low-molecularweight metal-binding proteins or peptides described in other plants and reported to be involved in metal tolerance. In the mechanism of copper tolerance at the leaf level, fractions III-1 (M_r 3700), III-2 (M_r 66000), and IV (M_r 2000) appear to have a role, fraction IV being specifically induced in the tolerant cultivar by Cu(II). Fractions III-1 and III-2 could participate in a different mechanism, adaptive in character, involving an enhanced capacity to bind copper in Cu-tolerant plants.Abbreviations DEAE diethylaminoethyl - M_r relative molecular mass - SDS sodium dodecyl sulfate - PAGE polyacrylamide-gel electrophoresis J.M. Palma was the recipient of a research fellowship from the Caja General de Ahorros y Monte de Piedad de Granada and CSIC. We are grateful to Dr. J. Moreno-Carretero, R + D Department, UNIASA, Granada, for conducting the amino-acid analyses. This work was supported by grant 603/275 from CAICYT-CSIC (Spain).     

Expression of the C3-C4 intermediate character in somatic hybrids between Brassica napus and the C3-C4 species Moricandia arvensis

The wild crucifer Moricandia arvensis is a potential source of alien genes for the genetic improvement of related Brassica crops. In particular M. arvensis has a C₃-C₄ intermediate photosynthetic mechanism which results in enhanced recapture of photorespired CO₂ and may increase plant water-use efficiency. In order to transfer this trait into Brassica napus, somatic hybridisations were made between leaf mesophyll protoplasts from cultured M. arvensis shoot tips and hypocotyl protoplasts from three Brassica napus cultivars, Ariana, Cobra and Westar. A total of 23 plants were recovered from fusion experiments and established in the greenhouse. A wide range of chromosome numbers were observed among the regenerated plants, including some apparent mixoploids. Thirteen of the regenerated plants were identified as nuclear hybrids between B. napus and M. arvensis on the basis of isozyme analysis. The phenotypes of these hybrids were typically rather B. napus-like, but much variability was observed, including variation in flower colour, leaf shape and colour, leaf waxiness, fertility and plant vigour. CO₂ compensation point measurements on the regenerated plants demonstrated that 3 of the hybrids express the M. arvensis C₃-C₄ intermediate character at the physiological level. Semi-thin sections through leaf tissues of these 3 plants revealed the presence of a Kranz-like leaf anatomy characteristic of M. arvensis but not found in B. napus. This is the first report of the expression of this potentially important agronomic trait, transferred from Moricandia, in M. arvensis x B. napus hybrids.     

Iron-efficient and iron-inefficient oats and corn respond differently to iron-deficiency stress

Iron-efficient (WF9 corn and Coker 227 oat) and Fe-inefficient (ys₁ corn and TAM 0–312 oat) cultivars were comparatively tested for their response to Fe-deficiency stress induced by the use of either ferrous or ferric chelators. Corn and oats were grown in 20 M Fe with 0, 60, and 120 M BPDS and 40 M Fe with 0, 120, and 240 M BPDS and 20 M Fe with 0 and 40 M EDDHA. All four cultivars tested, both Fe-efficient and Fe-inefficient, continuously reduced Fe³⁺ to Fe²⁺ at a low level as evidenced by the production of Fe²⁺ (BPDS)₃ in test nutrient solutions over time. Severity of chlorosis increased as more BPDS was added to the nutrient solutions for both WF9 and ys₁ corn, but unlike corn, Coker 227 and TAM 0-312 oats were both able to obtain Fe from the Fe²⁺ (BPDS)₃ complex and were less chlorotic as a result. In short-term (4-hour) in vivo measurements, iron-stressed WF9 (Fe-efficient) corn reduced more Fe³⁺ to Fe²⁺ than similarly stressed ys₁ corn, Coker 227 oat or TAM 0-312 oat. Thus, at the same time that Fe-efficient WF9 corn reduces more Fe than the other cultivars, it is also unable to compete with BPDS for that Fe in the nutrient solution. These differences coupled with the observation that only Coker 227 oat produced measureable iron solubilizing substances (phytosiderophores) suggest that these two species differ in their mechanisms for obtaining Fe during Fe-deficiency stress.     

Transport of glycine-betaine by Listeria monocytogenes

Uptake of [¹⁴C]glycine-betaine by Listeria monocytogenes was stimulated by NaCl with optimal stimulation at 0.4–0.5 M. The glycine-betaine transport system had a K _m of 22 M and a V _max of 11.7 nmol^-1 min^-1 mg^-1 protein when grown in the absence of NaCl. When grown in the presence of 0.8 M NaCl the V _max increased to 27.0 nmol^-1 min^-1 mg^-1 protein in 0.8 M NaCl. At NaCl concentrations above 0.5 M the uptake rate of glycine-betaine was reduced. Measurement of intracellular K⁺ concentrations and fluorescent dye quenching indicated that higher NaCl concentrations also led to a decrease in the electrochemical potential difference across the cytoplasmic membrane. Uptake of glycine was also observed, but this was not stimulated by NaCl.     

Effects of CaSO4 and NaCl on growth and nitrogen fixation ofLeucaena leucocephala

Effects and interactions of varying CaSO₄ and NaCl levels on growth and nitrogen fixation ofLeucaena leucocephala K8 were examined. Leucaena was grown in nutrient solution at four levels of CaSO₄ (0.5, 1.0, 2.5 and 5.0 mM) and NaCl (1, 25, 50 and 100 mM) in randomized blocks with five replications. While NaCl significantly reduced plant growth, additions of CaSO₄ increased plant height, leaf number, and biomass of salt treated plants. For the nonsaline treatments, high CaSO₄ levels slightly depressed growth, which contradicts suggestions that Leucaena has a high calcium requirement. A significant calcium/sodium interaction was not seen for nodule number or weight. Nodule number was significantly depressed by 100 mM NaCl and nodule weight of the salt stressed plants significantly increased as CaSO₄ concentration increased from 0.5 to 2.5 mM. Effects of NaCl and CaSO₄ on nitrogen content of plant parts were inconclusive. The promotion of Leucaena salinity tolerance by addition of CaSO₄ may be attributed to the effect of calcium in maintaing the selective permeability of membranes.     

Alleviation of salt stress by low dose γ-irradiation in rice

The effects of salt stress on the growth, photosynthesis, and antioxidative ability of the rice (Oryza sativa L.) plants raising from -irradiated seeds were investigated using two cultivars, Ilpumbyeo and Sanghaehyanghyella. The 50 and 100 mM NaCl solutions caused a remarkable decrease of the early germination rate and seedling growth. However, the salt stress-induced inhibition of the growth was significantly alleviated in the -irradiated plants. The chlorophyll contents and the effective quantum yield of photosystem 2 ( _{PS 2}) were lower in the NaCl-treated plants than in the control ones, while the non-photochemical quenching was higher in the former ones. Activities of the antioxidant enzymes such as superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased with increasing NaCl concentrations, and the irradiated groups had even higher SOD and APX activities than the non-irradiated ones. These alleviation effects were observed similarly in both the cultivars tested.     

Successful crosses between Festuca arundinacea Schreb. and Dactylis glomerata L.

Summary Five F₁ plants have been obtained after extensive crossing between different ecotypes or varieties of Festuca arundinacea Schreb. and Dactylis glomerata L. The success did not appear to depend on specific treatments (spraying with -aminocaproic acid or gibberellic acid or pre-pollination with killed pollen from the seed parent), but the crossability is limited to exceptional plants.F₁ hybrids showed characteristics of both the parents. In four hybrids various developmental disturbances were observed (low viability, aneusomaty, absence of development of inflorescences). Only one hybrid consistently showed 2n=35 chromosomes, good viability and growth, however, it was sterile. After clonal propagation, attempts for polyploidization were started.     

Manganese Absorption and Transport in Rice

The absorptive patterns of Mn²⁺ in excised rice roots, leaf tissues and intact plants, were studied. The rates of absorption of Mn²⁺ followed different patterns in the roots and the leaf tissues. The uptake from 0.1 and 5 mM MnSO₄ was found to be sensitive to metabolic inhibitors. The time course of uptake from 0.1 mM and 5 mM MnSO₄ followed a biphasic pattern which represented only the metabolic component of absorption. A secondary biphasic pattern of uptake at 5 mM MnSO₄ (one at 20 min and another at 80 min) appears quite anomalous and is probably related to structural virations or cellular compartments. When absorption and transport of Mn²⁺ were measured in intact rice and wheat plants, it was found that Mn²⁺ was easily translocated to shoot from roots and the transport of Mn²⁺ was comparable to that of K⁺.     

Responses of nitrogen-fixing and nitrate-supplied alfalfa (Medicago sativa L.) to iron chelates in an alkaline hydroponic medium

Ferric ethylenediamine di-(o-hydroxyphenylacetate) (FeEDDHA) and ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) were evaluated as Fe sources for hydroponic growth of alfalfa (Medicago sativa L., cv. Mesilla), either dependent on N₂ fixation or supplied with NO₃. The hydroponic medium was maintained at pH 7.5 by addition of CaCO₃. Nitrogen-fixing cultures were inoculated with Rhizobium meliloti 102 F51 and grown in medium without added nitrogen. After five to seven weeks of growth under greenhouse conditions, plants were harvested. Nitrogen fixation was measured by the acetylene reduction method.When FeEDDHA was supplied, growth of alfalfa, whether dependent on N₂ fixation or supplied with NO₃, was severely limited at concentrations typically used in hydroponic medium (10 or 20 M). Maximum yield of NO₃-supplied alfalfa was obtained at 100 M while maximum yield of N₂-fixing alfalfa was obtained in the range of 33 to 200 M FeEDDHA. Nodule fresh weights and N₂ fixation rates increased with FeEDDHA concentration up to 33 M and remained essentially constant up to 200 M. With FeHEDTA, maximum yields of both NO₃-grown and N₂-fixing alfalfa were obtained at 10 M. Growth of NO₃-supplied plants was inhibited at 200 M FeHEDTA while growth of N₂-fixing plants was inhibited at 100 M FeHEDTA. The numbers of nodules per plant increased between 3.3 and 10 M FeHEDTA; however, inhibition of nodule formation occurred at a concentration of 33 M or higher. Nodule weights per plant and N₂ fixation rates were depressed at 3.3 M as well as at 100 M FeHEDTA. The results suggest that alfalfa dependent on N₂ fixation is more sensitive to limited Fe availability than alfalfa supplied with NO₃.     

Characterization of the NADH dehydrogenase and fumarate reductase of Fibrobacter succinogenes subsp. succinogenes S85

Conditions promoting maximal in vitro activity of the particulate NADH:fumarate reductase from Fibrobacter succinogenes were determined. This system showed a pH optimum of 6.0 in K⁺ MES buffer only when salt (NaCl or KCl) was present. Salt stimulated the activity eightfold at the optimal concentration of 150m M. This effect was due to stimulation of fumarate reductase activity as salt had little effect on NADH: decylubiquinone oxidoreductase (NADH dehydrogenase). The stimulation of fumarate reductase by salt at pH 6.0 was not due to removal of oxaloacetate from the enzyme. Kinetic parameters for several inhibitors were also measured. NADH dehydrogenase was inhibited by rotenone at a single site with a K _i of 1 M. 2-Heptyl-4-hydroxyquinonline-N-oxide (HOQNO) inhibited NADH: fumarate reductase with a K _i of 0.006 M, but NADH dehydrogenase exhibited two HOQNO inhibition constants of approximately 1 M and 24 M. Capsaicin and laurylgallate each inhibited NADH dehydrogenase by only 20% at 100 M. NADH dehydrogenase gave K _m values of 1 M for NADH and 4 M for reduced hypoxanthine adenine dinucleotide.Published with the approval of the Director of the Agricultural Experiment Station, North Dakota State University, as journal article no. 2201     

Effects of salt on growth,ion accumulation,photosynthesis and leaf anatomy of the mangrove,<Emphasis Type="Italic"> Bruguiera parviflora</Emphasis>

The effects of a range of salinity (0, 100, 200 and 400 mM NaCl) on growth, ion accumulation, photosynthesis and anatomical changes of leaves were studied in the mangrove, Bruguiera parviflora of the family Rhizophoraceae under hydroponically cultured conditions. The growth rates measured in terms of plant height, fresh and dry weight and leaf area were maximal in culture treated with 100 mM NaCl and decreased at higher concentrations. A significant increase of Na⁺ content of leaves from 46.01 mmol m^-2 in the absence of NaCl to 140.55 mmol m^-2 in plants treated with 400 mM NaCl was recorded. The corresponding Cl^- contents were 26.92 mmol m^-2 and 97.89 mmol m^-2. There was no significant alteration of the endogenous level of K⁺ and Fe²⁺ in leaves. A drop of Ca²⁺ and Mg²⁺ content of leaves upon salt accumulation suggests increasing membrane stability and decreased chlorophyll content respectively. Total chlorophyll content decreased from 83.44 g cm^-2 in untreated plants to 46.56 g cm^-2 in plants treated with 400 mM NaCl, suggesting that NaCl has a limiting effect on photochemistry that ultimately affects photosynthesis by inhibiting chlorophyll synthesis (ca. 50% loss in chlorophyll). Light-saturated rates of photosynthesis decreased by 22% in plants treated with 400 mM NaCl compared with untreated plants. Both mesophyll and stomatal conductance by CO₂ diffusion decreased linearly in leaves with increasing salt concentration. Stomatal and mesophyll conductance decreased by 49% and 52% respectively after 45 days in 400 mM NaCl compared with conductance in the absence of NaCl. Scanning electron microscope study revealed a decreased stomatal pore area (63%) in plants treated with 400 mM NaCl compared with untreated plants, which might be responsible for decreased stomatal conductance. Epidermal and mesophyll thickness and intercellular spaces decreased significantly in leaves after treatment with 400 mM NaCl compared with untreated leaves. These changes in mesophyll anatomy might have accounted for the decreased mesophyll conductance. We conclude that high salinity reduces photosynthesis in leaves of B. parviflora, primarily by reducing diffusion of CO₂ to the chloroplast, both by stomatal closure and by changes in mesophyll structure, which decreased the conductance to CO₂ within the leaf, as well as by affecting the photochemistry of the leaves.     

Relative importance of Na+, Cl−, and abscisic acid in NaCl induced inhibition of root growth of rice seedlings

The relative importance of endogenous abscisic acid (ABA), as well as Na⁺ and Cl^– in NaCl-induced responses related to growth in roots of rice seedlings were investigated. The increase in ammonium, proline and H₂O₂ levels, and cell wall peroxidase (POD) activity has been shown to be related to NaCl-inhibited root growth of rice seedlings. Increasing concentrations of NaCl from 50 to 150 mM progressively decreased root growth and increased both Na⁺ and Cl^–. Treatment with NaCl in the presence of 4,4-diisothiocyano-2,2-disulfonic acid (DIDS, a nonpermeating amino-reactive disulfonic acid known to inhibit the uptake of Cl^–) had less Cl^– level in roots than that in the absence of DIDS, but did not affect the levels of Na⁺, and responses related to growth in roots. Treatment with 50 mM Na-gluconate (the anion of which is not permeable to membrane) had similar Na⁺ level in roots as that with 100 mM NaCl. It was found that treatment with 50 mM Na-gluconate effected growth reduction and growth-related responses in roots in the same way as 100 mM NaCl. All these results suggest that Cl^– is not required for NaCl-induced responses in root of rice seedlings. Endogenous ABA level showed no increase in roots of rice seedlings exposed to 150 mM NaCl. It is unlikely that ABA is associated with NaCl-inhibited root growth of rice seedlings.     

Effects of cadmium and nickel on in vivo carbon dioxide exchange rate of pigeon pea (Cajanus cajan L.)

Effects of acidic soil factors (Al, H-ion, Mo, and Mn) upon the soybean (Glycine max (L.) Merr. cv. Essex)/Bradyrhizobium japonicum symbiosis were examined in acidified soil. Plants were grown under full sunlight in pots containing N-deficient soil (pH 6.7) or similar soil amended with sufficient Al₂(SO₄)₃ or elemental S to give soil pH values of 4.8 and 4.6, respectively, and water-extractable Al levels of 30 and 14 M, respectively. Other treatments consisted of the addition of inorganic N or inoculation with commercial or locally-isolated B. japonicum. Acidification did not reduce shoot or root weights of plants receiving inorganic N but reduced (P0.05) shoot and root dry weights, nodule dry weights and numbers, shoot N concentrations, and chlorophyll levels of inoculated plants. Shoot dry weights and nodulation of inoculated plants were greater (P0.05) in Al₂(SO₄)₃-amended soil than in S-amended soil. Addition of Mo was not beneficial. It was concluded that reduced plant growth was caused by the effects of acidified soil on nodulation and that H-ion toxicity was probably the most limiting factor. Effects of Al, Mn, or Mo appeared less likely.     

The effect of copper toxicity on the contents of nitrogen compounds in Silene vulgaris (Moench) Garcke

The effect of copper on the uptake of nitrogen and the tissue contents of inorganic nitrogen, amino acids and proteins were studied in cooper-sensitive Silene vulgaris (Moench) Garcke, grown at different nitrogen sources (NH₄ ⁺ or NO₃ ^-). All the toxic copper levels tested, i.e. 4, 8, 16 M Cu²⁺, strongly inhibited the uptake of nitrogen, especially of NO₃ ^-, and decreased the content of NO₃ ^-, amino acids and proteins. Especially at 4 and 8 M Cu²⁺, NH₄ ⁺ accumulated in the plants, suggesting that the conversion of NH₄ ^- into amino acids was inhibited.     

Dissolution of ferric phosphate by alfalfa (Medicago sativa L.) root exudates

Alfalfa (Medicago sativa L.) was grown in hydroponic culture to investigate adaptation to Fe-deficiency. Root exudates released into the nutrient solution from Fe-deficient plants were trapped and condensed on an amberlite XAD-4 resin column. The diethyl ether fraction of these exudates dissolved ferric phosphate remarkably. The dissolving capability was about 62 times higher than that of root exudates obtained from Fe-sufficient plants in complete nutrient solution. The Fe-dissolving compound was separated and identified. It was a new natural compound with molecular formula C₁₄H₁₀O₅ and was identified as 2-(3,5-dihydroxyphenyl)-5,6-dihydroxybenzofuran by means of mass spectrometry and ¹H-nuclear magnetic resonance. This new compound worked as a phytoalexin and inhibited completely the fungal growth of Fusarium oxysporum f. sp. phaseoli.