Vanadium and plant nutrition: the growth of lettuce (lactuca sativa L.) and tomato (lycopersicon esculentum mill.) plants in nutrient solutions low in vanadium

Lettuce (Lactuca sativa L.) and tomato (Lycopersicon esculentum Mill.) plants were grown in purified nutrient solutions with and without the addition of 50 nanograms per milliliter V. These experiments showed that lettuce and tomato plants can be grown to maturity on nutrient solutions containing less than 0.04 nanogram per milliliter V with tissue concentrations of less than 2 to 18 nanograms per gram V. Growth and dry matter yield were comparable to those of plants grown on nutrient solutions containing 50 nanograms per milliliter with tissue levels of V from 117 to 418 nanograms per gram. Thus if V is an essential element for lettuce and tomato plants, the adequate tissue level would be less than 2 nanograms per gram V derivable from a growth medium containing less than 0.04 nanogram per milliliter V.     

Nickel: a micronutrient essential for higher plants

Nickel was established as an essential micronutrient for the growth of temperate cereal crops. Grain from barley (Hordeum vulgare L. cv `Onda'; containing 40 to 80 nanograms of Ni per gram dry weight) grown in solution culture with negligible Ni concentrations (< 30 nanograms of Ni per liter) exhibited greatly reduced germination rates (i.e. 50% less than grain from Ni-adequate plants) and seedling vigor of the viable grain was greatly depressed. Grain containing less than 30 nanograms per gram dry weight was inviable. Under Ni-deficient conditions, barley plants fail to produce viable grain because of a disruption of the maternal plant's normal grain-filling and maturation processes that occur following formation of the grain embryo. The observations that (a) barley plants fail to complete their life cycle in the absence of Ni and (b) addition of Ni to the growth medium completely alleviates deficiency symptoms in the maternal plants satisfies the essentiality criteria; thus, Ni should be considered a micronutrient for cereals. Because Ni is required by legumes, and is now established as essential for cereals, we conclude that Ni should be added to the list of micronutrients essential for all higher plant growth.     

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.     

A method to compare the effect of ionic iron and iron chelates in nutrient solution cultures

A method is described by which the effect of chelated Fe can be compared with the effect of ionic Fe in nutrient solution cultures over a prolonged period of time. Plants are grown in two solutions in succession: the one containing all nutrient elements except Fe, the other one containing the Fe compound together with Ca(NO₃)₂. In experiments with soybeans (Glycine maxima (L.) Merr.) and with corn (Zea mays L.) it was shown that a 7-day cycle with the ratio of 4 days nutrient solution to 3 days Fe solution resulted in growth and Fe nutrition similar to plants grown with a normal nutrient solution.     

Association of Potassium and Some Other Monovalent Cations with Occurrence of Polyphosphate Bodies in Chlorella pyrenoidosa

Phosphate-starved Chlorella pyrenoidosa cells formed polyphosphate bodies (PB) upon transfer into nutrient solutions containing phosphate and potassium, or another monovalent cation, such as Na⁺, NH₄⁺, Li⁺, or Rb⁺. The phenomenon was studied by chemical analyses, light microscopy, and electron microscopy.

When the P-starved cells were transferred into a complete nutrient solution containing 100 micromolar P, they accumulated large quantities of P and K within several hours. The accumulation was accompanied by a corresponding appearance of PB in the cells. The absence of K from the medium prevented appreciable P accumulation and PB formation, but omitting Ca or Mg did not.

The P-starved cells exposed to a simple solution of at least 20 micromolar H₃PO₄ and 100 micromolar KHCO₃ responded in a similar manner as the cells exposed to the complete nutrient solution. However, the PB appeared structurally different.

It is proposed that monovalent cations are essential for PB formation in C. pyrenoidosa. K is suggested to be a major component of PB formed in K-sufficient media.

     

Living plant cells released from the root cap: A regulator of microbial populations in the rhizosphere?

Barley (Hordeum vulgare L. cv. ‘Onda’) plants were grown in nutrient solutions supplied either 0 (no Ni added), 0.6, or 1.0 μM NiSO₄. Plants supplied 0 μM Ni developed Ni deficiency symptoms; Ni deficiency resulted in the disruption of nitrogen metabolism, and affected the concentration of malate and various inorganic anions in roots, shoots, and grain of barley. The concentrations of 10 of the 11 soluble amino acids determined were 50–200% higher in 30-day-old shoots of plants supplied inadequate Ni levels than in shoots of Ni-supplied plants. The total concentration of all amino acids determined was higher in roots and grain of Ni-deficient plants. Concentrations of NO₃ ^- and Cl^- were also higher in Ni-deficient barley shoots than in Ni-sufficient barley shoots. In contrast, the concentration of alanine in shoots of Ni-deficient barley was reduced to one-third of the concentration in Ni-sufficient plants. The shoot concentrations of malate and SO₄ ^2- were also depressed under Ni-deficient conditions. Total nitrogen concentration in grain, but not in shoots, of Ni-deficient plants was significantly increased over that found in Ni-adequate plants. Nickel deficiency results in marked disruptions of N metabolism, malate and amino acid concentrations in barley. These results are discussed in view of the possible roles of Ni in plants. Supported, in part, by an ITT International Fellowship awarded to PHB and administered by the Institute for International Education, United Nations Plaza, New York, NY. This research was part of the program of the Center for Root-Soil Research. Supported, in part, by an ITT International Fellowship awarded to PHB and administered by the Institute for International Education, United Nations Plaza, New York, NY. This research was part of the program of the Center for Root-Soil Research.     

Translocation of nickel in xylem exudate of plants

Topped plants of tomato (Lycopersicon esculentum), cucumber (Cucumis sativus), corn (Zea mays), carrot (Daucus carota), and peanut (Arachis hypogaea) were treated with 0.5 to 50 micromolar Ni (containing ⁶³Ni) in nutrient solutions. Xylem exudate was collected for 10 hours or, in the case of corn, for 20 hours at 5-hour intervals. Electrophoresis of nutrient solution distributed all Ni cathodically as inorganic Ni²⁺. Low concentrations of Ni in tomato exudate migrated anodically, presumably bound to organic anion (carrier). However, this carrier became saturated at about 2 micromolar Ni in exudate, and excess Ni ran cathodically. Most of the Ni in cucumber, corn, carrot, and peanut exudate ran anodically, and its migration rate was identical for all exudates. Peanut root sap contained 14 to 735 micromolar Ni. The anodic Ni carriers in root sap and exudate appear identical. The carrier in root sap became saturated near 100 micromolar Ni, as shown by cathodic streaking of Ni exceeding that concentration. It appears that all five species translocate low concentrations of Ni in the same anionic form.     

Increased Sporulation of Vesicular-Arbuscular Mycorrhizal Fungi by Manipulation of Nutrient Regimens

Adjustment of pot culture nutrient solutions increased root colonization and sporulation of vesicular-arbuscular mycorrhizal (VAM) fungi. Paspalum notatum Flugge and VAM fungi were grown in a sandy soil low in N and available P. Hoagland nutrient solution without P enhanced sporulation in soil and root colonization of Acaulospora longula, Scutellospora heterogama, Gigaspora margarita, and a wide range of other VAM fungi over levels produced by a tap water control or nutrient solutions containing P. However, Glomus intraradices produced significantly more spores in plant roots in the tap water control treatment. The effect of the nutrient solutions was not due solely to N nutrition, because the addition of NH₄NO₃ decreased both colonization and sporulation by G. margarita relative to levels produced by Hoagland solution without P.     

Iron-stress Response in Mixed and Monocultures of Soybean Cultivars

Hawkeye (Fe-efficient) and PI-54619-5-1 (Fe-inefficient) soybeans (Glycine max [L.] Merr.) were grown in mixed and monoculture nutrient solutions to evaluate an inhibitory effect of PI-54619-5-1 on the uptake of Fe by Hawkeye. The ability of Hawkeye to take up Fe (Fe-stress response) was dependent on the degree of Fe stress (Fe deficiency) and was not the result of an inhibitory substance released by PI-54619-5-1 in mixed culture (Hawkeye + PI-54619-5-1).     

New insights into the mechanism of nickel insertion into carbon monoxide dehydrogenase: analysis of Rhodospirillum rubrum carbon monoxide dehydrogenase variants with substituted ligands to the [Fe3S4] portion of the active-site C-cluster

Carbon monoxide dehydrogenase (CODH) from Rhodospirillum rubrum catalyzes the oxidation of CO to CO₂. A unique [NiFe₄S₄] cluster, known as the C-cluster, constitutes the active site of the enzyme. When grown in Ni-deficient medium R. rubrum accumulates a Ni-deficient apo form of CODH that is readily activated by Ni. It has been previously shown that activation of apo-CODH by Ni is a two-step process involving the rapid formation of an inactive apo-CODH•Ni complex prior to conversion to the active holo-CODH. We have generated CODH variants with substitutions in cysteine residues involved in the coordination of the [Fe₃S₄] portion of the C-cluster. Analysis of the variants suggests that the cysteine residues at positions 338, 451, and 481 are important for CO oxidation activity catalyzed by CODH but not for Ni binding to the C-cluster. C451S CODH is the only new variant that retains residual CO oxidation activity. Comparison of the kinetics and pH dependence of Ni activation of the apo forms of wild-type, C451S, and C531A CODH allowed us to develop a model for Ni insertion into the C-cluster of CODH in which Ni reversibly binds to the C-cluster and subsequently coordinates Cys531 in the rate-determining step.     

Temperature and oxygen effects on C-photosynthate unloading and accumulation in developing soybean seeds

The environmental sensitivity of the processes associated with the import of photosynthate by developing soybean seeds was investigated within intact fruit and with excised, immature embryos. Intact pods of field-grown (Glycine max [L.] Merr.) Amsoy 71 soybeans were subjected to localized regimes of 0, 21, or 100% O₂ and 15, 25, or 35°C during pulsechase translocation experiments and, 2.5 hours later, the uptake and distribution of ¹⁴C-photosynthate among dissected fruit tissues determined. In other experiments, excised embryos were incubated in [¹⁴C]sucrose solutions under various experimental conditions to separate the effects of these treatments on accumulation by the embryos from those which may operate on phloem unloading in the maternal seedcoat.     

Effects of Ni Deficiency on Some Nitrogen Metabolites in Cowpeas (Vigna unguiculata L. Walp)

Cowpeas grown in nutrient solutions, from which Ni had been removed by a ligand exchange technique, accumulated urea in most tissues. Urea levels were highest (up to 3.1 percent dry weight) in necrotic leaf tips. Urea accumulation in Ni-deficient cowpea tissues amounted to about 1 percent of the total N. The accumulation of urea was presumably associated with the catabolism of N compounds in older tissues and the redistribution of N catabolites within the plant during the reproductive growth. The exclusion of N salts from the nutrient media at a late stage of growth, either with or without added Ni, led to a general amelioration of urea accumulation and a lower level of the related amino acid, arginine, in root and stem tissue. Plant leaves that contained toxic levels of urea and displayed necrotic symptoms had tissue Ni levels ranging from less than 0.01 to 0.15 μg Ni per gram dry weight. Nickel concentrations in tissue from plants not treated with Ni, were initially very low, but increased as the cowpeas matured. Apparently, there was a source of Ni contamination in the Ni-deficient growth media which provided a source of Ni for uptake by the plants during growth. Ureide levels were low and unaffected by Ni deprivation. No evidence for free purines or uric acid accumulation in plant tissues could be found. It is hypothesized that Ni (and urease) participates in the normal N metabolism of these plants during the reproductive phase of growth.     

On the mechanism of aging in soybean seeds

Changes in seeds of soybeans (Glycine max [L.] Merr. var. Wayne) which occur during accelerated aging (41 C, 100% relative humidity) showed subsequent loss of vigor, a decline in early respiratory activity, increased leakage of electrolytes, losses of as much as 10% dry weight from imbibing cotyledons, and a decrease in the swelling response of the imbibing system (seed plus H₂O). Each of these changes with aging is interpreted as resulting from deteriorative changes in membranes.     

Purine catabolism in plants : purification and some properties of inosine nucleosidase from yellow lupin (lupinus luteus L.) seeds

Inosine nucleosidase (EC 3.2.2.2), the enzyme which hydrolyzes inosine to hypoxanthine and ribose, has been partially purified from Lupinus luteus L. cv. Topaz seeds by extraction of the seed meal with low ionic strength buffer, ammonium sulfate fractionation, and chromatography on aminohexyl-Sepharose, Sephadex G-100, and hydroxyapatite.

Molecular weight of the native enzyme is 62,000 as judged by gel filtration. The inosine nucleosidase exhibits optimum activity around pH 8. Energy of activation for inosine hydrolysis estimated from Arrhenius plot is 14.2 kilocalories per mole. The K_m value computed for inosine is 65 micromolar.

Among the inosine analogs tested, the following nucleosides are substrates for the lupin inosine nucleosidase: xanthosine, purine riboside (nebularine), 6-mercaptopurine riboside, 8-azainosine, adenosine, and guanosine. The ratio of the velocities measured at 500 micromolar concentration of inosine, adenosine, and guanosine was 100:11:1, respectively. Specificity (V_max/K_m) towards adenosine is 48 times lower than that towards inosine.

In contrast to the adenosine nucleosidase activity which is absent from lupin seeds and appears in the cotyledons during germination (Guranowski, Pawełkiewicz 1978 Planta 139: 245-247), the inosine nucleosidase is present in both lupin seeds and seedlings.

     

The timing and rate of phytic Acid accumulation in developing soybean seeds

The time-course of phosphorus (P) accumulation in the phytic acid fraction of developing soybean (Glycine max [L.] Merr. cv `Williams 79') seeds as well as the relation of phytic acid P to total P content were determined. Phytic acid was detected early in embryogenesis in field-grown soybeans and accumulated in a linear fashion throughout most of seed development. Although the observed rates of accumulation ranged from 18.7 micrograms phytic acid P per seed per day in pods positioned low on the plant to 33.6 micrograms in pods positioned high on the plant, the final concentrations were the same in all cases. Nearly all of the P translocated to developing seeds was incorporated into phytic acid from the third week after flowering until physiological maturity, with the sum of nonphytic acid P compounds remaining constant. Phytic acid accumulation was also linear throughout development when soybean plants were grown in solutions having nutrient P levels that ranged from severely limiting (2.0 milligrams P per liter) to excess (50 milligrams P per liter). However, there was a pronounced effect on rate of accumulation, which ranged from 7.2 micrograms phytic acid per seed per day with limiting nutrient P to 44.7 micrograms with excess P. The change in level of phytic acid accounted for most of the alteration in total seed P that was caused by altering the P status of the plants. These results support the view that phytic acid synthesis is involved in P homeostasis of the developing soybean seed.     

Compartmental efflux analysis and removal of extracellular cadmium from roots

Profiles of ¹⁰⁹Cd efflux from roots into three solutions were determined for young intact plants of Agrostis gigantea and maize. The solutions were (a) nutrient culture medium containing 3 micromolar Cd at room temperature, (b) ice-cold 5 millimolar CaCl₂, and (c) ice-cold 5 millimolar PbCl₂. Efflux profiles were clearly resolved into three easily discernible components having fast, medium, and slow exchange rates. These results were unexpected for the situation where some intracellular Cd was present both as extractable Cd-binding peptide and in electron-dense granules within the cytoplasm and the vacuoles. Adding a fourth compartment to the curve-fitting model produced a splitting of the fast exchanging component. Use of these efflux kinetics to estimate Cd fluxes through membranes was inappropriate. However, they were useful in determining optimal washing times for the removal of extracellular Cd. A 10 minute wash in ice-cold 5 millimolar CaCl₂ is recommended for this purpose for Agrostis and maize roots.     

Long distance translocation of sucrose, serine, leucine, lysine, and carbon dioxide assimilates: I. Soybean

To determine the selectivity of movement of amino acids from source leaves to sink tissues in soybeans (Glycine max [L.] Merr. `Wells'), ¹⁴C-labeled serine, leucine, or lysine was applied to an abraded spot on a fully expanded trifoliolate leaflet, and an immature sink leaf three nodes above was monitored with a GM tube for arrival of radioactivity. Comparisons were made with ¹⁴C-sucrose and ¹⁴CO₂ assimilates. Radioactivity was detected in the sink leaf for all compounds applied to the source leaflet. A heat girdle at the source leaf petiole essentially blocked movement of applied compounds, suggesting phloem transport. Transport velocities were similar (ranged from 0.75 to 1.06 cm/min), but mass transfer rates for sucrose were much higher than those for amino acids. Hence, the quantity of amino acids entering the phloem was much smaller than that of sucrose. Extraction of source, path, and sink tissues at the conclusion of the experiments revealed that 80 to 90% of the radioactivity remained in the source leaflet. Serine was partially metabolized in the transport path, whereas lysine and leucine were not. Although serine is found in greater quantities than leucine and lysine in the source leaf and path of soybeans, applied leucine and lysine were transported at comparable velocities and in only slightly lower quantities than was applied serine. Thus, no selective barrier against entry of these amino acids into the phloem exists.     

Volatile metabolites controlling germination in buried weed seeds

Velvetleaf (Abutilon theophrasti Medic), morning glory (Ipomoea purpurea [L.] Roth), and wild mustard (Brassica kaber [D.C.] L. C. Wheeler) seeds exhibited decreased germination with increased planting depth in soil. Flushing the soil for 2 minutes each day with air overcame the inhibition. A sealed in vitro system was used to sample the volatile components produced by weed seeds. Inhibition of seed germination was accompanied by decreased O₂ levels and production of volatile metabolites identified as acetaldehyde, ethanol, and acetone. The effectiveness of these compounds in reducing germination was dependent on O₂ levels.     

Host-Pathogen Interactions: XIV. Isolation and Partial Characterization of an Elicitor from Yeast Extract

An elicitor of glyceollin accumulation in soybeans (Glycine max L.) has been isolated from a commercially available extract of brewers' yeast. Yeast is not a known pathogen of plants. The elicitor was isolated by precipitation in 80% (v/v) ethanol followed by column chromatography on DEAE-cellulose, sulfopropyl-Sephadex, and concanavalin A-Sepharose. Compositional and structural analysis showed the elicitor to be a glucan containing terminal, 3-, 6-, and 3,6-linked glucosyl residues. The yeast elicitor stimulates the accumulation of glyceollin in the cotyledons and hypocotyls of soybeans when as little as 15 nanograms or 100 nanograms of the elicitor is applied to the respective tissues. The yeast elicitor is very similar in both structure and absolute elicitor activity to an elicitor isolated from the mycelial walls of Phytophthora megasperma var. sojae, a pathogen of soybeans. These and other results of this laboratory suggest that plants are able to respond to the presence of a wide range of fungi by recognizing, as foreign to the plant, structural polysaccharides of the mycelial walls of the fungi.     

Importance of Environmental pH during Root Development on Phosphate Absorption

Wheat seedlings (Triticum aestivum L. cv Gamenya) were grown for 4 days in culture solutions of differing pH prior to studying their subsequent short-term absorption of ³²Pi from solutions of the same or different pH.

Increasing pH of the absorption solution from 5.5 to 7.0 or 8.0 depressed ³²Pi absorption from 1 and 10 micromolar Pi but had little effect at 100 and 1000 micromolar Pi. Increasing the pH of the culture solution from 4.5 to 6.5 doubled or trebled subsequent ³²Pi absorption from nearly all absorption solutions over a wide range of Pi concentrations, pH, and nutrient compositions.

When seedlings were transferred between culture pH treatments 4.5 and 6.5, their capacity for ³²Pi absorption remained unchanged for at least 5 hours and adjusted by 60 to 80% after 24 hours and completely after 48 hours. This suggests that the root's capacity to absorb Pi responds to pH through slow structural changes in its mechanism of Pi absorption. P content and concentration of wheat seedlings reflected the response of ³²Pi absorption to culture pH.

It is suggested that absorption pH affects an activity component of the process for Pi absorption and culture pH affects a capacity component. Failure to recognize the capacity component of the pH response explains why previously published results for short-term ³²Pi absorption conflict with those for long-term P accumulation in plants.