Plant Nutrient Solution Research Articles

Bacterial culture history affects the attachment of Bradyrhizobium japonicum to host Glycine max roots

To understand the physiological control of attachment of Bradyrhizobium japonicum, bacterial growth and preincubation conditions were varied before exposing the bacteria (104 cfu mL−1) to excised soybean root segments. The attachment rate of strain USDA 110 was constant through a 7-h exposure (0.9% of the population attached per hour). Maximal attachment of strain USDA 110 occurred during log phase and for strains USDA 76 and USDA 31, during early stationary phase. The ability of log-phase cultures to attach to roots was significantly correlated with their competitive ability to nodulate soybean. Cells of strains USDA 110 attached to roots were isolated and reexposed to roots 15 times over a 6-month period. No significant increase in attachment ability of these serially exposed bacteria was observed (a mean of 1.4% of the population attached at each 2-h exposure). Attachment was stimulated 2.4- to 7-fold when cells of strains USDA 110 or USDA 31 were preincubated in a minus-nitrogen plant nutrient solution and on new cell growth. The stimulation of attachment could not be mimicked by preconditioning cells in solutions of NaCl, CaCl2, or CaSO4 of the same normality as the nutrient solution. The ability of B. japonicum strains to attach to host roots is a dynamic property affected by growth medium, culture age, and cell pretreatment conditions. The progeny of attached cells adhered to roots in the same low proportions as cells not previously exposed to roots. Key words: rhizobia, adhesion, competition, bacterial pretreatment.

Competitiveness of indigenous populations of Bradyrhizobium japonicum serocluster 123 as determined using a root-tip marking procedure in growth pouches

Soil Bradyrhizobium populations limit nodule occupancy of soybean by symbiotically-superior inoculant strains throughout much of the American midwest. In this study, the competitiveness of indigenous populations of B. japonicum serocluster 123 from Waukegan and Webster soils was evaluated in growth pouches using a root-tip marking procedure. The native rhizobia were from soils incubated 0–8 h in soybean root exudate (SRE) or plant nutrient solution (PNS) prior to inoculation. Populations of serocluster 123 strains in soil and nodule occupancy by these strains were assessed using fluorescent antibodies prepared against B. japonicum USDA 123. There were no significant differences in populations that came from SRE or PNS incubated soils: both populations increased in number over the incubation period. Nodule occupancy by both populations in growth pouches was similar to that previously encountered in field studies with these two soils. With the Waukegan soil, the serocluster 123 population dominated nodulation forming 69 and 62% of taproot nodules above and below the root tip mark, respectively. However, for the more alkaline Webster soil, serocluster 123 strains were much less competitive, producing only 9 and 13%, respectively, of the nodules formed above and below the root tip mark. In growth pouches, soil populations of bradyrhizobia from the Webster soil produced significantly more nodules than those from the Waukegan soil, but both strains and a pure culture of USDA 110 had a similar distribution of nodules.

Effect of nickel deficiency in soybeans on the phytotoxicity of foliar-applied urea

The leaf-tip necrosis commonly observed after foliar fertilization of soybean [Glycine max (L.) Merr.] plants with urea is usually attributed to ammonia formed through hydrolysis of urea by plant urease. We recently found, however, that although addition of a urease inhibitor (phenylphosphorodiamidate) to foliar-applied urea increased the urea content and decreased the ammonia content and urease activity of soybean leaves, it increased the leaf-tip necrosis observed after foliar fertilization. We concluded that this necrosis was due to accumulation of toxic amounts of urea rather than formation of toxic amounts of ammonia. To confirm this conclusion, we measured the urea content, urease activity, and leaf-tep necrosis of leaves of soybean plants treated with urea after growth of the plants in nutrient solutions containing different amounts of nickel (Ni), which is an essential component of urease. We found that the urease activity of these leaves decreased, and that their urea content and leaf-tip necrosis increased, with decrease in the Ni content of the nutrient solution. Besides supporting the conclusion that the leaf-tip necrosis observed after foliar fertilization of soybean with urea is due to accumulation of toxic amounts of urea in the soybean leaves, these observations indicate that Ni-deficient plants may have a lower urease activity than plants that are not deficient in Ni and may therefore be more susceptible to leaf burn when foliar-fertilized with urea.

Short exposure to Azospirillum brasilense Cd inoculation enhanced proton efflux of intact wheat roots

Inoculation of wheat seedlings with Azospirillum brasilense Cd significantly increased the proton efflux of the roots 5 h after inoculation compared with noninoculated plants. Removal of the bacterial cells from the root surface 2, 4, or 10 h after inoculation did not affect proton extrusion, which remained similar to the proton efflux of inoculated roots with a permanent A. brasilense Cd population. Proton efflux from roots after short exposure to A. brasilense Cd was directly related to the inoculation level and to the physiological status of the bacterial cells. Active bacteria, at an optimal level for inoculation (105–107 cfu∙mL−1), produced the most proton extrusion from roots. Stressed bacteria, i.e., bacteria exposed to starvation, 45 °C, anaerobic conditions, or a high level of streptomycin before inoculation, induced smaller but not statistically significant increases in proton efflux. Inoculation with dead A. brasilense Cd cells, cell-wall fragments, or several associative nonbeneficial rhizosphere bacteria belonging to other genera did not enhance the proton efflux compared with noninoculated plants. Continuous perfusion of the nutrient solution of plants while maintaining the bacterial cells in the root vicinity eliminated the proton efflux enhancement caused by A. brasilense Cd. Bacteria, regardless of species or stress conditions, in the absence of plants produced negligible proton efflux. It is suggested that short exposures of wheat roots to live A. brasilense Cd enhanced the proton efflux of roots, probably through the release of an as yet unidentified bacterial signal. Active metabolism of the bacterium is required for this enhancement, which is of a triggering nature. Key words: Azospirillum, beneficial bacteria, plant–bacteria interaction, proton efflux, rhizosphere bacteria, Triticum aestivum, wheat.

Accumulation of Apoplastic Iron in Plant Roots

We hypothesized that the resistance of Hawkeye (HA) soybean (Glycine max L.) to iron-deficiency induced chlorosis (IDC) is correlated to an ability to accumulate a large pool of extracellular-root iron which can be mobilized to shoots as the plants become iron deficient. Iron in the root apoplast was assayed after efflux from the roots of intact plants in nutrient solution treated with sodium dithionite added under anaerobic conditions. Young seedlings of HA soybean accumulated a significantly larger amount of extracellular iron in their roots than did either IDC-susceptible PI-54619 (PI) soybean or IDC-resistant IS-8001 (IS) sunflower (Helianthus annus L.). Concurrently, HA soybean had much higher concentrations of iron in their shoots than either PI soybean or IS sunflower. The concentration of iron in the root apoplast and in shoots of HA soybean decreased sharply within days after the first measurements of extracellular root iron were made, in both +Fe and -Fe treatments. The accumulation of short-term iron reserves in the root apoplast and translocation of iron in large quantities to the shoot may be important characteristics of IDC resistance in soybeans.

15 N 2 Fixation by Bacteria Associated with Maize Roots at a Low Partial O 2 Pressure

Nitrogen fixation by bacteria associated with roots of intact maize plants was measured by exposing the roots to N(2) at a partial O(2) pressure (pO(2)) of 2 or 10 kPa. The plants were grown in a mixture of Weswood soil and sand and then transferred to plastic cylinders containing an N-free plant nutrient solution. The solution was sparged continuously with a mixture of air and N(2) at a pO(2) of 2 or 10 kPa. Acetylene reduction was measured after the roots were exposed to the low pO(2) overnight. The air-N(2) atmosphere in the cylinders was then replaced with an O(2)-He atmosphere at the same pO(2), and the roots were exposed to 20 kPa of N(2) for 20 to 22 h. Incorporation of N into the roots was 200 times greater at 2 kPa of O(2) than at 10 kPa of O(2). Adding l-malate (1 g of C liter) to the nutrient solution increased root-associated nitrogenase activity, producing a strong N label which could be traced into the shoots. Fixed N was detected in the shoots within 5 days after the plants were returned to unfertilized soil. In a similar experiment with undisturbed plants grown in fritted clay, movement of fixed N into the shoots was evident within 4 days after the roots were exposed to N(2) at 2 kPa of O(2). Inoculation with Azospirillum lipoferum yielded no significant differences in shoot dry weight, total nitrogen content, percent nitrogen, or N enrichment of plant tissues. Inoculated plants did exhibit greater root dry weight than uninoculated plants, however.

Effect of Oxygen and Malate on NO3− Inhibition of Nitrogenase in Soybean Nodules

Soybean (Glycine max cv Hodgson) nitrogenase activity (C(2)H(2) reduction) in the presence or absence of nitrate was studied at various external O(2) tensions. Nitrogenase activity increased with oxygen partial pressure up to 30 kilopascals, which appeared to be the optimum. A parallel increase in ATP/ADP ratios indicated a limitation of respiration rate by low O(2) tensions in the nodule, and the values found for adenine nucleotide ratios suggested that the nitrogenase activity was limited by the rate of ATP regeneration. In the presence of nitrate, the nitrogenase activity was low and less stimulated by increased pO(2), although the nitrite content per gram of nodules decreased from 0.05 to 0.02 micromole when pO(2) increased from 10 to 30 kilopascals. Therefore, the accumulation of nitrite inside the nodule was probably not the major cause of the inhibition. Instead, inhibition by nitrate could be due to competition for reducing power between nitrate reduction and bacteroid or mitochondrial respiration inside the nodule. This is supported by the observation of decrease in ATP/ADP ratios from 1.65, in absence of nitrate, to 0.93 in the presence of this anion at 30 kilopascals O(2). Furthermore, the inhibition was suppressed by the addition, to the plant nutrient solution, of 15 millimolar l-malate, a carbon substrate that is considered to be the major source of reductant for the bacteroids in the symbiosis.

Plant growth responses to bacterization with selected Pseudomonas spp. strains and rhizosphere microbial development in hydroponic cultures

Increases in root and shoot fresh weight were observed when the nutrient solutions used for growth of tomato, cucumber, lettuce, and potato plants were bacterized with plant growth promoting Pseudomonas strains. It is hypothesized that plant growth promotion is due to the suppression of a deleterious rhizosphere microflora, especially deleterious endorhizosphere bacteria. The composition of the microbial community in artificial substrates, such as nutrient films and rockwool, is thought to be less complex than in soil. Therefore, development of a microflora deleterious for plant growth has to be anticipated. Microbial development in hydrocultures was simulated by preinoculating plant nutrient solutions with rhizosphere suspensions from plants that had been grown for different lengths of time in hydroponic cultures. After 16 days the plants in preinoculated nutrient solutions showed a growth reduction that correlated with the extent of root colonization by fluorescent pseudomonads in the endorhizosphere. Bacterization with plant growth promoting Pseudomonas sp. strain WCS417r counteracted this plant growth reduction. This increase in plant growth was accompanied by a dense colonization of the endorhizosphere by WCS417r and by a consequent displacement of indigenous endorhizosphere-inhabiting pseudomonads.Key words: Pseudomonas, endorhizosphere, hydroponics, plant growth, colonization.

Effects of cation leaching on mineral cycling and transpiration: investigations with beech seedlings, Fagus sylvatica L.

Beech seedlings (Fagus sylvatica L.) were sprayed with acidic or ammonium-rich solutions of different concentrations, 10-3 or 10-5 mol l-1 H+ or NH4 + . Whilst the leaching of Ca and Mg was increased by the more acid treatment, the K leaching was decreased. On the other hand, the concentrated NH4 + mist led to a substantial increase in the leaching of K. As a consequence of the greater uptake of cations due to their leaching, more protons were released to the nutrient solution and into the rhizosphere of potted plants. Increased transpiration was observed following the application of acidic mist to the plants in nutrient solution but decreased stomatal diffusive resistance of potted plants was detected only at night. Acid mist caused changes in stomatal behaviour that were responsible for a rapid and greater water loss of detached leaves.

Molybdenum limitation of asymbiotic nitrogen fixation in forests of Pacific Northwest America

Nitrogenase activity as measured by acetylene reduction and nitrogen fixation as measured by 15N 2 uptake is widespread in forest litter, decaying wood and the lichen Lobaria in Pacific Northwest forests. In all cases the activity of nitrogenase is enhanced by addition of plant nutrient solutions and this is shown to be a specific molybdenum effect. A wide range of forest species have litter which supports nitrogen fixation during decay and the majority show molybdenum stimulation. The effect is most prominent in the acid soils situated between the Coast Range and the Cascade Range and extends from Oregon through Washington to British Columbia. Nitrogenase is increased quantitatively by Mo additions and the effect, though best seen in the laboratory, is also measurable in the field. The results are discussed on the basis of geographical distribution of the effect, plant species and the likely role of asymbiotic nitrogen fixation in contributing to long-term nutrient cycling.

INFLUENCE OF SYNTHETIC CHELATING AGENTS ON THE SPECIATION OF COPPER, ZINC AND MANGANESE IN PLANT NUTRIENT SOLUTIONS

Abstract A chemical equilibrium model of a typical plant nutrient solution was constructed and applied, in conjunction with an appropriate data base of equilibrium constants, to the program MINEQL. The output yielded the speciation of the metals in the nutrient solution. Additions of DTPA or EDTA were found to suppress the concentration of copper(II), zinc(II) and manganese(II) aquo ions, the relative decrease in concentration being more marked at pH 7.5 than at pH 4.3 in the case of DTPA but more marked at pH 4.3 than at pH 7.5 in the case of EDTA. These results were found to correspond to the trends observed in experimental observations on hydroponically cultivated bush beans. The results are interpreted in terms of the aquo ions of the three metals considered being the bioavailable species. The possible importance of copper(II)-hydroxy and other dissolved copper(II) species as bioavailable forms was considered but no clear conclusions could be reached.

Evaluation of the symbiotic nitrogen-fixing potential of soils by direct microbiological means

A method for estimating the nitrogen-fixing capacity of a population of rhizobia resident in soil is presented. legume test plants, growing under microbiologically-controlled conditions in test tubes packed with a vermiculite substrate moistened with a nitrogen-free plant nutrient solution, are inoculated directly with a suspension of the soil under examination. Rhizobia in the soil nodulate the test plants, and the amount of foliage dry matter produced in the 28 days after inoculation is regarded as an index of their effectiveness. An inoculum of at least 30, and preferably 100, rhizobia is needed to ensure that nitrogen fixation is not masked by delayed nodulation. The new method is tentatively described as the ‘whole-soil inoculation’ technique.

Suitable level of zinc, copper and manganese for mass production of the vesicular arbuscular mycorrhizal fungus,Glomus fasciculatum

There is no information on the role of micronutrients on the mass production of the vesicular arbuscular mycorrhizal fungi. Hence zinc, copper and managanese at 4 different levels in Ruakura plant nutrient solution viz. 1/4, 1/2 and double the recommended level were studied to select the suitable level for mass production ofGlomus fasciculatum inoculum raised inChloris gayana (Rhodes grass) using perlite: soilrite mix (1:1 by volume). Percentage root colonization, extramatrical chlamydospore number and number of infective propagules per unit weight of the inoculum were maximum at half the recommended level i.e. 0·18, 0·04, 0·73 mM of Zn, Cu and Mn respectively.

Mechanisms of inhibition of Gaeumannomyces graminis var. tritici by fluorescent pseudomonads

The take‐all fungus Gaeumannomyces graminis var. tritici reduced the weight of wheat plants grown in tubes containing sterilized sand and plant nutrient solution. Fluorescent pseudomonads, when added to the tubes, inhibited the take‐all fungus and increased plant weight. Iron (as FeNaEDTA) had no effect on the inhibition of the fungus by the pseudomonads. Some of the pseudomonads produced a compound in the wheat rhizosphere with a UV absorption peak at 365 nm, but the inhibition of G. graminis by pseudomonads was not proportional to the UV absorbance of rhizosphere extracts. A yellow crystalline compound, absorbing at 365 nm, was extracted from broth cultures and shown to be toxic to G. graminis under acid conditions. This compound is considered to be phenazine‐I‐carboxylic acid.

Versatile manifold for the simultaneous determination of ions in flow injection analysis

A flow injection analysis system is described for the simultaneous determination of several ions in a single sample using a combination of potentiometric and spectrophotometric detection. A composite manifold has been designed consisting of a flow cell containing four ion-selective electrodes and two spectrophotometric transducer flow cells. The system has been applied to the determination of K+, Ca2+, NH4+, Cl–, NO3– and PO43– ions in a number of plant nutrient solutions.

A hydroponic system for microgravity plant experiments.

The construction of a permanently manned space station will provide the opportunity to grow plants for weeks or months in orbit for experiments or food production. With this opportunity comes the need for a method to provide plants with a continuous supply of water and nutrients in microgravity. The Capillary Effect Root Environment System (CERES) uses capillary forces to maintain control of circulating plant nutrient solution in the weightless environment of an orbiting spacecraft. The nutrient solution is maintained at a pressure slightly less than the ambient air pressure while it flows on one side of a porous membrane. The root, on the other side of the membrane, is surrounded by a thin film of nutrient solution where it contacts the moist surface of the membrane. The root is provided with water, nutrients and air simultaneously. Air bubbles in the nutrient solution are removed using a hydrophobic/hydrophilic membrane system. A model scaled to the size necessary for flight hardware to test CERES in the space shuttle was constructed.

Whatever happened to geniponics?

Premium, plentiful produce that can be grown virtually anywhere year round was the goal in the 1970s of a team of engineers at General Electric's Syracuse, N.Y., facility. A variation on hydroponics-growing plants in nutrient solution rather than soil-Geniponics survived a 1980 sale to Control Data Corp. but went down in 1984 before rising electricity prices. However, similar systems live on in controlled-environment research at numerous universities and research centers.

Leaf Magnesium Alters Photosynthetic Response to Low Water Potentials in Sunflower

We grew sunflower (Helianthus annuus L.) plants in nutrient solutions having nutritionally adequate but low or high Mg(2+) concentrations and determined whether photosynthesis was effected as leaf water potentials (psi(w)) decreased. Leaf Mg contents were 3- to 4-fold higher in the plants grown in high Mg(2+) concentrations (10 millimolar) than in those grown in low concentrations (0.25 millimolar). These contents were sufficient to support maximum growth, plant dry weight, and photosynthesis, and the plants appeared normal. As low psi(w) developed, photosynthesis was inhibited but moreso in high Mg leaves than in low Mg leaves. The effect was particularly apparent under conditions of light- and CO(2)-saturation, indicating that the chloroplast capacity to fix CO(2) was altered. The differential inhibition observed in leaves of differing Mg contents was not observed in leaves having differing K contents, suggesting that the effect may have been specific for Mg. Because Mg(2+) inhibits photophosphorylation and coupling factor activities at concentrations likely to occur as leaves dehydrate, Mg may play a role in the inhibition of chloroplast reactions at low psi(w), especially in leaves such as sunflower that markedly decrease in water content as psi(w) decreases.

Effect of acidic precipitation on bean plants

Direct and indirect effects of acidic precipitation on the rates of CO2 exchange of bean plants (Phaseolus vulgaris L., cv. Tendergreen) were measured. Solutions of HCl, HNO3, H2SO4, and artificial acid rain at pH values from 2.7 to 5.0 sprayed on leaves at intervals (varying from 1 to 5 days in different experiments) for 3 weeks had no effect on rates of CO2 exchange. Some lesions appeared on leaves where chlorophyll was destroyed; apparently undamaged areas of the leaf compensated by increasing the rate of photosynthesis. Application of acidic solutions to pot soil in which the plants were growing or growing plants in nutrient solutions at pH 3.0 caused serious effects in the leaves, resembling Ca or Mg deficiency symptoms, but no obvious deleterious effects to the roots. Effects of acid were greater when Ca, Mg, P, or N were supplied at reduced concentration. Reducing the concentration of K, Fe, or the mixture of trace elements normally supplied did not influence the effect of acidity of the nutrient solution. The uptake and distribution of Ca, Mg, P, and N throughout the plant was not affected by the acid treatments. It is concluded that acidic soil water or nutrient solutions interfere with the metabolism of calcium, magnesium, phosphorus, and nitrogen in the leaves.

Effect of lectin on nodulation by wild-type Bradyrhizobium japonicum and a nodulation-defective mutant.

The nodulation characteristics of wild-type Bradyrhizobium japonicum USDA 110 and mutant strain HS111 were examined. Mutant strain HS111 exhibits a delayed-nodulation phenotype, a result of its inability to initiate successful nodulation promptly following inoculation of the soybean root. Previously, we showed that the defect in initiation of infection leading to subsequent nodulation which is found in HS111 can be phenotypically reversed by pretreatment with soybean root exudate or soybean seed lectin. This effect is not seen after pretreatment with root exudates and lectins obtained from other plant species. Treatment of strain HS111 with as little as 10 soybean seed lectin molecules per bacterium (3.3 X 10 (-12) M) resulted in enhancement of nodule formation. Pretreatment of wild-type B. japonicum USDA 110 with soybean root exudate or seed lectin increased nodule numbers twofold on 6-week-old plants. Wild-type strain USDA 110 cells inoculated at 10(4) cells per seedling exhibited a delay in initiation of infection leading to subsequent nodulation. Wild-type cells pretreated in soybean root exudates or seed lectin did not exhibit a delay in nodulation at this cell concentration. Mutant strain HS111 pretreated in seed lectin for 0 or 1 h, followed by washing with the hapten D-galactose to remove the lectin, exhibited a delay in initiation of nodulation. Phenotypic reversal of the delayed-nodulation phenotype exhibited by strain HS111 was seen if incubation was continued for an additional 71 h in plant nutrient solution following 1 h of lectin pretreatment. Reversal of the delayed-nodulation phenotype of HS111 through lectin pretreatment was prevented by chloramphenicol or rifampin.(ABSTRACT TRUNCATED AT 250 WORDS)