Antagonistic effects of abscisic acid and jasmonates on salt stress-inducible transcripts in rice roots

Abscisic acid (ABA) and jasmonates have been implicated in responses to water deficit and wounding. We compared the molecular and physiological effects of jasmonic acid (JA) (< or = 10 microM), ABA, and salt stress in roots of rice. JA markedly induced a cationic peroxidase, two novel 32- and 28-kD proteins, acidic PR-1 and PR-10 pathogenesis-related proteins, and the salt stress-responsive SalT protein in roots. Most JA-responsive proteins (JIPs) from roots also accumulated when plants were subjected to salt stress. None of the JIPs accumulated when plants were treated with ABA. JA did not induce an ABA-responsive group 3 late-embryogenesis abundant (LEA) protein. Salt stress and ABA but not JA induced oslea3 transcript accumulation. By contrast, JA, ABA, and salt stress induced transcript accumulation of salT and osdrr, which encodes a rice PR-10 protein. However, ABA also negatively affected salT transcript accumulation, whereas JA negatively affected ABA-induced oslea3 transcript levels. Endogenous root ABA and methyl jasmonate levels showed a differential increase with the dose and the duration of salt stress. The results indicate that ABA and jasmonates antagonistically regulated the expression of salt stress-inducible proteins associated with water deficit or defense responses.

Response of the water status of soybean to changes in soil water potentials controlled by the water pressure in microporous tubes

Water transport through a microporous tube-soil-plant system was investigated by measuring the response of soil and plant water status to step change reductions in the water pressure within the tubes. Soybeans were germinated and grown in a porous ceramic 'soil' at a porous tube water pressure of -0.5 kpa for 28 d. During this time, the soil matric potential was nearly in equilibrium with tube water pressure. Water pressure in the porous tubes was then reduced to either -1.0, -1.5 or -2.0 kPa. Sap flow rates, leaf conductance and soil, root and leaf water potentials were measured before and after this change. A reduction in porous tube water pressure from -0.5 to -1.0 or -1.5 kPa did not result in any significant change in soil or plant water status. A reduction in porous tube water pressure to -2.0 kPa resulted in significant reductions in sap flow, leaf conductance, and soil, root and leaf water potentials. Hydraulic conductance, calculated as the transpiration rate/delta psi between two points in the water transport pathway, was used to analyse water transport through the tube-soil-plant continuum. At porous tube water pressures of -0.5 to-1.5 kPa soil moisture was readily available and hydraulic conductance of the plant limited water transport. At -2.0 kPa, hydraulic conductance of the bulk soil was the dominant factor in water movement.

Immunolocalization of PsNLEC-1, a lectin-like glycoprotein expressed in developing pea nodules

The pea (Pisum sativum) nodule lectin gene PsNlec1 is a member of the legume lectin gene family that is strongly expressed in infected pea nodule tissue. A full-length cDNA sequence of PsNlec1 was expressed in Escherichia coli and a specific antiserum was generated from the purified protein. Immunoblotting of material from isolated symbiosomes revealed that the glycoprotein was present in two antigenic isoforms, PsNLEC-1A and PsNLEC-1B. The N-terminal sequence of isoform A showed homology to an eight-amino acid propeptide sequence previously identified from the cDNA sequence of isoform B. In nodule homogenates the antiserum recognized an additional fast-migrating band, PsNLEC-1C. Fractionation studies indicated that PsNLEC-1C was associated with a 100,000 g nodule membrane fraction, suggesting an association with cytoplasmic membrane or vesicles. Immunogold localization in pea nodule tissue sections demonstrated that the PsNLEC-1 antigen was present in the symbiosome compartment and also in the vacuole but revealed differences in distribution between infected host cells in different parts of the nodule. These data suggest that PsNLEC-1 is subject to posttranslational modification and that the various antigenic isoforms can be used to monitor membrane and vesicle targeting during symbiosome development.

Changes in soluble sugar, starch, and alcohol dehydrogenase in Arabidopsis thaliana exposed to N2 diluted atmospheres

Proper exchange of atmospheric gases is important for normal root and shoot metabolism in plants. This study was conducted to determine how restricted air supply affects foliar carbohydrates, while using the marker enzyme alcohol dehydrogenase (ADH) to report on the oxygenation status of the rootzone. Fourteen-day-old Arabidopsis thaliana (L.) Heynh. plants grown singly in 7-ml tubes containing agarified nutrient medium were placed in coupled Magenta vessels and exposed for six days to either ambient air or one of six different air/nitrogen dilutions. Redox potential of the agar medium was measured immediately after harvesting and freezing leaf tissue, and then root systems were quickly extracted from the agar and frozen for subsequent analyses. Redox potential measurements indicated that this series of gas mixtures produced a transition from hypoxia to anoxia in the root zones. Root ADH activity increased at higher rates as the redox potential neared anoxic levels. In contrast, ADH mRNA expression quickly neared its maximum as the medium became hypoxic and showed little further increase as it became anoxic. Foliar carbohydrate levels increased 1.5- to 2-fold with decreased availability of metabolic gases, with starch increasing at higher concentrations of air than soluble carbohydrate. The results serve as a model for plant performance under microgravity conditions, where absence of convective air movement prevents replenishment of metabolic gases.

The N-acetylgalactosamine and lactosamine specific lectin from Iris hybrida leaves

The lectin isolated from the leaves of Iris hybrida binds specifically N-acetyl-galactosamine and lactose. Its molecule consists of two identical subunits bound by disulfide bonds. The lectin is a glycoprotein containing about 12% of sugars. It binds asialoglycoproteins containing complex type sugar chains. The binding is reduced by half at the concentration of 0.15 to 0.40 mM of the galactose containing disaccharides irrespectively to a type of galactose isomer. This indicates rather broad specificity of I. hybrida leaf lectin.

An immunoreactive protein to wheat-germ agglutinin antibody is induced in oat roots following invasion of the cereal cyst nematode Heterodera avenae, and by jasmonate

A protein that cross-reacts to a wheat-germ agglutinin antibody was induced in oat roots following the invasion of second-stage juveniles (J2) of the cereal cyst nematode Heterodera avenae. This protein, designated ASP45, was acid soluble, and its molecular mass was about 45 kDa on a sodium dodecyl sulfate-polyacrylamide gel. ASP45 was induced in both compatible and incompatible interactions between the nematode and the plant, and also in roots by exposure to jasmonic acid (JA) or methyl jasmonate. However, ASP45 was not induced by elicitors of pathogenesis-related proteins, abscisic acid, or wounding. Lipoxygenase activity, which is involved in JA synthesis, was higher in nematode-infected and JA-treated roots than in their noninfected, untreated counterparts. Inhibition of lipoxygenase activity in roots abolished ASP45 induction in the nematode-infected roots. Amino acid sequences similar to that of ASP45 were found in chitinases of poplar tree and Arabidopsis, even though ASP45 showed no chitinase activity. Although the biological role of ASP45 in infected roots is not clear, JA is suggested to be involved in signal transduction after pathogen invasion of the plant.

Expression of an Antirrhinum dihydroflavonol reductase gene results in changes in condensed tannin structure and accumulation in root cultures of Lotus corniculatus (bird's foot trefoil)

Condensed tannins (proanthocyanidins) are an important factor in the nutritive and dietary quality of many forage crops. We report here experiments aimed at altering the levels and monomer composition of condensed tannins (CTs) in 'hairy root' cultures of Lotus corniculatus (bird's foot trefoil) using genetic manipulation. An Antirrhinum majus dihydroflavonol reductase (DFR) cDNA was expressed in sense in L. corniculatus and CT levels in transgenic root cultures were analysed. Two co-transformed lines were noted with decreased CT content relative to controls and these levels were comparable with antisense-DFR phenotypes. In ADFR10, a co-transformed line with the highest CT levels, CT structure was altered in a manner consistent with the substrate specificity of the introduced gene; that is an increase in pro-pelargonidin monomers noted after hydrolysis of CTs. RT-PCR confirmed the expression of endogenous DFR gene(s) in both putatively co-suppressed lines and also in ADFR10. Analysis of selected root culture lines indicated that the monomer composition of CTs did not change during growth and development but that levels of CTs varied in a regulated manner.

Evidence that elevated CO2 levels can indirectly increase rhizosphere denitrifier activity

We examined the influence of elevated CO2 concentration on denitrifier enzyme activity in wheat rhizoplanes by using controlled environments and solution culture techniques. Potential denitrification activity was from 3 to 24 times higher on roots that were grown under an elevated CO2 concentration of 1,000 micromoles of CO2 mol-1 than on roots grown under ambient levels of CO2. Nitrogen loss, as determined by a nitrogen mass balance, increased with elevated CO2 levels in the shoot environment and with a high NO3- concentration in the rooting zone. These results indicated that aerial CO2 concentration can play a role in rhizosphere denitrifier activity.

Two hemoglobin genes in Arabidopsis thaliana: the evolutionary origins of leghemoglobins

We cloned two hemoglobin genes from Arabidopsis thaliana. One gene, AHB1, is related in sequence to the family of nonsymbiotic hemoglobin genes previously identified in a number of plant species (class 1). The second hemoglobin gene, AHB2, represents a class of nonsymbiotic hemoglobin (class 2) related in sequence to the symbiotic hemoglobin genes of legumes and Casuarina. The properties of these two hemoglobins suggest that the two families of nonsymbiotic hemoglobins may differ in function from each other and from the symbiotic hemoglobins. AHB1 is induced, in both roots and rosette leaves, by low oxygen levels. Recombinant AHB1 has an oxygen affinity so high as to make it unlikely to function as an oxygen transporter. AHB2 is expressed at a low level in rosette leaves and is low temperature-inducible. AHB2 protein has a lower affinity for oxygen than AHB1 but is similar to AHB1 in having an unusually low, pH-sensitive oxygen off-rate.

Health impacts of large releases of radionuclides. Physical transport and chemical and biological processes in agricultural systems

The purpose of radioecological models is to make realistic estimates of doses to the public after accidental releases of radionuclides into the environment. Important physical, chemical and biological processes involved in the dispersion and transport of radioactive substances in the atmosphere and along the food-chains are presented. The results of the EURAD (EURopean Acid Deposition) model, predicting the deposition patterns of 131I and 137Cs in Belarus and Ukraine after the Chernobyl accident, are discussed. An overview of the most important ecological processes--such as deposition, interception and translocation, weathering, transfers from soil to plants and from plants to animal/animal products, and seasonality in agricultural environments--is given. Examples corresponding to these individual processes, mainly experimental results after the Chernobyl accident and related to radiocaesium and radioiodine, are shown and discussed.

Binding and electrostatic attraction of lanthanum (La3+) and aluminum (Al3+) to wheat root plasma membranes

A general model for the sorption of trivalent cations to wheat-root (Triticum aestivum L cv. Scout 66) plasma membranes (PM) has been developed and includes the first published coefficients for La3+ and Al3+ binding to a biological membrane. Both ions are rhizotoxic, and the latter ion is the principal contributor to the toxicity of acidic soils around the world. The model takes into account both the electrostatic attraction and the binding of cations to the negatively charged PM surface. Ion binding is modeled as the reaction P- + IZ <==> 'PIZ-1 in which P- represents a negatively charged PM ligand, located in an estimated area of 540 A2, and IZ represents an ion of charge Z. Binding constants for the reaction were assigned for K+ (1 M-1) and Ca2+ (30 M-1) and evaluated experimentally for La3+ (2200 M-1) and H+ (21,500 M-1). Al sorption is complicated by Al3+ hydrolysis that yields hydroxoaluminum species that are also sorbed. Binding constants of 30 and 1 M-1 were assigned for AlOH2+ and Al(OH)+2, respectively, then a constant for Al3+ (20,000 m-1) was evaluated experimentally using the previously obtained values for K+, Ca2+ and H+ binding. Electrostatic attraction was modeled according to Gouy-Chapman theory. Evaluation of parameters was based upon the sorption of ions to PM vesicles suspended in solutions containing variable concentrations of H+, Ca2+ and La3+ or Al3+. Use of small volumes, and improved assay techniques, allowed the measurement of concentration depletions caused by sorption to vesicles. Some independent confirmation of our model is provided by substantial agreement between our computations and two published reports of La3+ effects upon zeta potentials of plant protoplasts. The single published report concerning the electrostatic effects of Al on cell membranes is in essential agreement with the model.

Zrp2: a novel maize gene whose mRNA accumulates in the root cortex and mature stems

A near full-length cDNA clone (pZRP2) was isolated from a cDNA library constructed from maize root mRNAs. The predicted polypeptide has a calculated molecular mass of 66,975 Da, is largely hydrophilic, and contains 26 repeats of a motif the consensus sequence of which is RKATTSYG[S][D/E][D/E][D/E][D/E][P]. The function of the putative protein remains to be elucidated. The ZRP2 mRNA accumulates to the highest levels in young roots, and is also present in mature roots and stems of maize. Further analysis of young roots indicates that the lowest level of ZRP2 mRNA is near the root tip, with relatively high levels throughout the remainder of the root. In situ hybridization reveals that ZRP2 mRNA accumulates predominantly in the cortical parenchyma cells of the root. In vitro nuclear run-on transcription experiments indicate a dramatically higher level of zrp2 gene transcription in 3-day old roots than in 5-day old leaves. A zrp2 genomic clone, which includes the transcribed region and 4.7 kb of upstream sequence, was isolated and characterized.

Regulation of sulfur assimilation in higher plants: a sulfate transporter induced in sulfate-starved roots plays a central role in Arabidopsis thaliana

Proton/sulfate cotransporters in the plasma membranes are responsible for uptake of the environmental sulfate used in the sulfate assimilation pathway in plants. Here we report the cloning and characterization of an Arabidopsis thaliana gene, AST68, a new member of the sulfate transporter gene family in higher plants. Sequence analysis of cDNA and genomic clones of AST68 revealed that the AST68 gene is composed of 10 exons encoding a 677-aa polypeptide (74.1 kDa) that is able to functionally complement a Saccharomyces cerevisiae mutant lacking a sulfate transporter gene. Southern hybridization and restriction fragment length polymorphism mapping confirmed that AST68 is a single-copy gene that maps to the top arm of chromosome 5. Northern hybridization analysis of sulfate-starved plants indicated that the steady-state mRNA abundance of AST68 increased specifically in roots up to 9-fold by sulfate starvation. In situ hybridization experiments revealed that AST68 transcripts were accumulated in the central cylinder of sulfate-starved roots, but not in the xylem, endodermis, cortex, and epidermis. Among all the structural genes for sulfate assimilation, sulfate transporter (AST68), APS reductase (APR1), and serine acetyltransferase (SAT1) were inducible by sulfate starvation in A. thaliana. The sulfate transporter (AST68) exhibited the most intensive and specific response in roots, indicating that AST68 plays a central role in the regulation of sulfate assimilation in plants.

Gravitropic reaction in the growth of tea roots

In Japan, tea (Camellia sinenis (L.) Kuntze) seedlings are propagated by cutting. A root system of clonal plants by cutting consists of adventitious roots and lateral roots. Most of the roots grow horizontally, which results in a shallow distribution of the root system. Such a shallow root system could be one of the factors contributing to the deterioration of nutrient uptake and resistance to water stress. Gravitropism of the roots is considered to be a decisive factor that controls the depth of a root system. The authors have investigated changes in the growth direction of roots to gravitative stimulus, using several kinds of roots (seminal roots, lateral roots and adventitious roots). Furthermore, amyloplasts in the root-cap cells, which are considered to be an equipment sensing gravistimulus, were observed. Seminal roots prominently showed orthogravitropism and contained many amyloplast particles in their root cap cells. Most lateral and adventitious roots showed plagiogravitropism, growing in an angle to gravistimulus, and lacked observable amyloplast particles in their root cap cells. The results suggest that the shallowing of root systems of elonal tea plants could be attributed to a gravitropic reaction of the adventitious and lateral roots composing the root system. There could also be a close relationship between the growth direction of roots and the presence of amyloplasts in root-cap cells.

Sites of rDNA transcription are widely dispersed through the nucleolus in Pisum sativum and can comprise single genes

Incorporation by RNA polymerases of BrUTP into both plant root tissue and isolated plant nuclei as a method for localization of the sites of transcription has been used. In this paper pea root tissue was used, and under the conditions employed, nearly all the incorporation occurs in the nucleolus, and thus must be catalysed by RNA polymerase I. Immunofluorescence and confocal microscopy shows that incorporation occurs in a pattern consisting of many small foci distributed widely through the dense fibrillar component of the nucleoli. Immunogold labelling using silver-enhanced Nanogold probe at the electron microscopic level confirms the sites of transcription as small foci approximately 200 nm in diameter. Simultaneous fluorescence in situ hybridization with a probe to the external transcribed spacer (ETS) region of the pre-rRNA shows that the structures revealed by this probe and the BrUTP immunofluorescence labelling are very similar. A probe to the transcribed portion of the rDNA (18S) also shows a good correlation to the sites of BrUTP incorporation within the nucleolus. On the other hand a probe to the non-transcribed intergenic spacer region (NTS) shows very little coincidence with the sites of BrUTP incorporation, and double fluorescence in situ labelling with both 18S and NTS probes confirms this difference in localization. These results suggest that most BrUTP foci correspond to single transcribed genes.

A novel and simple model of the uptake of organic chemicals by vegetation from air and soil

A novel and simple three-compartment fugacity model has been developed to predict the kinetics and equilibria of the uptake of organic chemicals in herbaceous agricultural plants at various times, including the time of harvest using only readily available input data. The chemical concentration in each of the three plant compartments leaf, stem which includes fruits and seeds, and root) is expressed as a function of both time and chemical concentrations in soil and air. The model was developed using the fugacity concept; however, the final expressions are presented in terms of concentrations in soil and air, equilibrium partition coefficients and a set of transport and transformation half-lives. An illustrative application of the model is presented which describes the uptake of bromacil by a soybean plant under hydroponic conditions. The model, which is believed to give acceptably accurate prediction of the distribution of chemicals among plant tissues, air and soil, may be used for the assessment of exposure to, and risk from contaminants consumed either directly from vegetation or indirectly in natural and agricultural food chains.

Mannitol inhibits growth of intact cucumber but not pea seedlings by mechanically collapsing the root pressure

The positive xylem pressure (Px) in cucumber hypocotyls is a direct extension of root pressure and therefore depends on the root environment. Solutions of the electrolyte KCl (0-10 osm) reduced the hypocotyl Px transiently (biphasic response), while the Px reduction by mannitol solutions was sustained. The amplitudes of the induced Px reduction depended directly, and the degree of Px restoration after stress release depended indirectly, on the size of the initial positive Px indicating that mannitol released the root pressure by a mechanical rather than osmotic mechanism. Mannitol treatment and other means of root pressure reduction revealed two separate growth responses in the affected cucumber hypocotyls. Only steep Px drops (following root excision or root pressure release in mannitol) directly cause a rapid, transient drop in growth rate (GR). Both rapid and slow (after root incubation in KCN or NEM) decreases in root pressure, however, led to a sustained growth inhibition of cucumber hypocotyls after about 30 min. This delay characterizes the growth response as an indirect consequence of the Px change. Pea seedlings, which lacked root pressure and had a negative Px throughout, showed extremely small changes in epicotyl Px and GR after root incubation in mannitol. It is apparent that the higher sensitivity of cucumber growth to mannitol depended on the presence and release of root pressure.

Alternative splicing of cyclin transcripts in maize endosperm

Cyclins are the regulatory subunits of cyclin-dependent protein kinases. In investigations of the expression of a cyclin gene during maize endosperm development, we detected a cyclin transcript with a 63-bp deletion in the region encoding the conserved 'cyclin box' where cyclin interacts with p34cdc2, the catalytic domain of the cyclin-dependent protein kinase. Analysis of cDNA and genomic sequences, and other observations, indicated that the deletion was caused by alternative splicing of a retained intron in the normally spliced transcript. Whereas the normally spliced cyclin RNA was mitotically functional, as indicated by its ability to promote maturation of Xenopus oocytes, the alternatively spliced transcript was unable to promote maturation. In addition to maize endosperm, the alternatively spliced cyclin was detected in apical meristem, mature leaf, root tip and mature root.

Inhibition of morphine tolerance and dependence by Withania somnifera in mice

Chronic treatment with Withania somnifera (Ws) (family: Solanaceae, 100 mg/kg) commercial root extract followed by saline on days 1-9 failed to produce any significant change in tailflick latency from the saline pretreated group in mice. However, repeated administration of Ws (100 mg/kg) for 9 days attenuated the development of tolerance to the analgesic effect of morphine (10 mg/kg). Ws (100 mg/kg) also suppressed morphine-withdrawal jumps, a sign of the development of dependence to opiate as assessed by naloxone (2 mg/kg) precipitation withdrawal on day 10 of testing.

Acidic phosphoprotein complex of the 60S ribosomal subunit of maize seedling roots. Components and changes in response to flooding

We determined that ribosomes of seedling roots of maize (Zea mays L.) contain the acidic phosphoproteins (P-proteins) known to form a flexible lateral stalk structure of the 60S subunit of eukaryotic ribosomes. The P-protein stalk, composed of P0, P1, and P2, interacts with elongation factors, mRNA, and tRNA during translation. Acidic proteins of 13 to 15.5 kD were released as a complex from ribosomes with 0.4 M NH4Cl/50% ethanol. Protein and cDNA sequence analysis confirmed that maize ribosomes contain one type of P1, two types of P2, and a fourth and novel P1/P2-type protein. This novel P-protein, designated P3, has the conserved C terminus of P1 and P2. P1, P2, and P3 are similar in deduced mass (11.4-12.2 kD) and isoelectric point (4.1-4.3). A 35.5- to 36-kD acidic protein was released at low levels from ribosomes with 1.0 M NH4Cl/50% ethanol and identified as P0. Labeling of roots with [32P]inorganic phosphate confirmed the in vivo phosphorylation of the P-proteins. Flooding caused dynamic changes in the P-protein complex, which affected the potential of ribosome-associated kinases and casein kinase II to phosphorylate the P-proteins. We discuss possible alterations of the ribosomal P-protein complex and consider that these changes may be involved in the selective translation of mRNA in flooded roots.

Cadmium- and copper-induced changes in tomato membrane lipids

Cadmium and copper uptake and distribution, as well as their effects on growth and lipid composition were investigated in 17-day-old tomato seedlings (Lycopersicon esculentum Mill. cv. 63/5 F1) grown in culture solution supplied with two concentrations of Cd or Cu (0, 5 and 50 microM). The accumulation of Cd and Cu increased with external metal concentrations, and was considerably higher in roots than in primary leaves. Biomass production of the growing roots and primary leaves was strongly depressed at high metal levels. Also, significant decreases in the content of lipid classes and changes of fatty acid composition were recorded in heavy metal-stressed plants in comparison with controls. Glycolipid contents were decreased more in leaves than in roots by Cd-treatment, but copper decreased both to similar extents in both organs. Likewise, both metals reduced the phospholipid and neutral lipid contents more in roots than in leaves. In almost all lipid classes the proportion of palmitic acid (16:0) increased, and that of linoleic (18:2) or linolenic (18:3) acid decreased, suggesting that heavy metal treatment induced an alteration in the fatty acid desaturation processes. Furthermore, the accumulation of palmitate (16:0) rather than stearate (18:0) indicated an alteration in the ratio of products from the fatty acid synthase. Copper was found to be the most unfavourable for plant growth and lipid metabolism. The possible mechanisms by which heavy metals, especially Cu, induce a strong lipid shift are discussed.

Proton and calcium flux oscillations in the elongation region correlate with root nutation

The involvement of Ca2+ and H+ flux oscillations in root nutation was studied for decapped roots of corn (Zea mays L. cv. Aussie Gold) placed horizontally. Net ion fluxes were measured around the elongation and meristematic regions using a microelectrode ion flux measuring system. High correlation between H+ flux oscillations and root nutations was found in the elongation region. Two oscillatory components of H+ flux, with periods of about 90 min and 7 min, correlated with root circumnutations and micronutations, respectively. The periods of H+ flux oscillations and rhythmical root movements in this region could be modified similarly by external factors including pH. In the meristematic region no association between ion flux behaviour and nutation was apparent. Ion flux oscillations and nutations both decreased in amplitude as the growth rate at the measured location decreased. Possible involvement of ion flux oscillations in root circumnutation is discussed. It is concluded that a model involving an internal oscillator must be developed to explain the H+ flux involvement in root nutations.

Biological activities of pseudomycin A, a lipodepsinonapeptide from Pseudomonas syringae MSU 16H

Similarly to other Pseudomonas lipodepsinonapeptides, pseudomycin A inhibits proton extrusion from maize roots, promotes closure of stomata in Vicia faba, necrosis of tobacco leaves, haemolysis of human erythrocytes, affects H(+)-ATPase activity and proton translocation in plasma membrane vesicles, and stimulates succinate respiration in pea mitochondria. In general, the biological activities of pseudomycin A are lower than those of syringomycin-E, the prototype member of this family of bacterial metabolities. This difference might depend on the diverse number and distribution of charged residues in the peptide moiety of these compounds.

cDNA clones encoding 1,3-beta-glucanase and a fimbrin-like cytoskeletal protein are induced by Al toxicity in wheat roots

A cDNA library made from mRNA of Al-treated roots of an Al-sensitive wheat (Triticum aestivum cv Victory) cultivar was screened with a degenerate oligonucleotide probe derived from the partial amino acid sequence of the Al-induced protein TAI-18. Of seven clones that initially hybridized with the probe, one encoded a novel 1,3-beta-glucanase having a calculated molecular weight of 46.3 and an isoelectric point of 6.0. Like the A6 1,3-beta-glucanase gene products from Brassica napus and Arabidopsis thaliana, the predicted wheat protein had a C-terminal extension with three potential glycosylation sites. Northern analysis revealed that wheat 1,3-beta-glucanase mRNA was up-regulated in Al-intoxicated roots, with highest expression after 12 h. The antibody to A6 1,3-beta-glucanase from B. napus cross-reacted with a 56-kD protein that was induced after 24 h. A second partial cDNA clone showed similarity to genes encoding cytoskeletal fimbrin-like (actin-bundling) proteins. Although well studied in animals and fungi, fimbrins have not previously been described in plants. Fimbrin-like transcripts were up-regulated after 24 h of Al treatment in the Al-sensitive wheat cv Victory. In the Al-tolerant cv Atlas 66, fimbrin-like mRNA was up-regulated within 12 h by Al concentrations that did not inhibit root growth. Cellular stress associated with Al toxicity therefore causes up-regulation of a defense-related gene and a gene involved in the maintenance of cytoskeletal function.

Cellular differentiation regulated by gibberellin in the Arabidopsis thaliana pickle mutant

The plant growth regulator gibberellin (GA) has a profound effect on shoot development and promotes developmental transitions such as flowering. Little is known about any analogous effect GA might have on root development. In a screen for mutants, Arabidopsis plants carrying a mutation designated pickle (pkl) were isolated in which the primary root meristem retained characteristics of embryonic tissue. Expression of this aberrant differentiation state was suppressed by GA. Root tissue from plants carrying the pkl mutation spontaneously regenerated new embryos and plants.

Determination of sodium in biological materials by instrumental neutron activation analysis

A formalized method for determining sodium in biological materials by instrumental neutron activation analysis is presented. The method includes common procedures from the numerous options available to this historically nonformalized analytical technique. The number of procedural options is restricted to minimize the method's complexity, yet the method is still applicable to a variety of neutron activation facilities. High accuracy and precision are achieved by placing bounds on allowed uncertainty at critical stages of the analysis. Analytical results from the U.S. Food and Drug Administration laboratory and 4 other laboratories demonstrate the method's performance.

A group 3 LEA cDNA of rice, responsive to abscisic acid, but not to jasmonic acid, shows variety-specific differences in salt stress response

A cDNA clone oslea3, encoding a group 3 late-embryogenesis abundant (LEA) protein was isolated from roots of rice seedlings (Oryza sativa L.). The encoded OSLEA3 protein has previously been found to accumulate to higher levels in roots of two salt-tolerant compared to a salt-sensitive rice variety in response to abscisic acid (ABA) [Moons et al., 1995. Plant Physiol. 107, 177-186]. The OSLEA3 protein (Mr 20.5, pI 6.5) characteristically contains ten imperfect 11-mer amino acid repeats. Exogenous application of ABA and exposure to salt shock (150 mM NaCl) rapidly induces a de novo, abundant oslea3 transcript accumulation in seedling roots, whereas application of jasmonic acid (9 microM) does not induce oslea3 expression. The stress-induced oslea3 transcript gradually declined upon prolonged salt shock, as wilting-induced damage became irreversible. oslea3 expression was compared for the salt-tolerant variety Pokkali and the salt-sensitive cultivar Taichung N1. Higher maximal mRNA levels were found in roots of the tolerant variety, also declining less rapidly upon sustained salt shock, concomitant with a delayed drop in shoot water content. DNA blot analysis indicated the existence of a small oslea3 gene family in rice with an equal gene number in both ecotypes. The results suggest that a differential regulation of oslea3 expression is an aspect of the varietal differences in salt stress tolerance.

Gravity, light and plant form

Plants have evolved highly sensitive and selective mechanisms that detect and respond to various aspects of their environment. As a plant develops, it integrates the environmental information perceived by all of its sensory systems and adapts its growth to the prevailing environmental conditions. Light is of critical importance because plants depend on it for energy and, thus, survival. The quantity, quality and direction of light are perceived by several different photosensory systems that together regulate nearly all stages of plant development, presumably in order to maintain photosynthetic efficiency. Gravity provides an almost constant stimulus that is the source of critical spatial information about its surroundings and provides important cues for orientating plant growth. Gravity plays a particularly important role during the early stages of seedling growth by stimulating a negative gravitropic response in the primary shoot that orientates it towards the source of light, and a positive gravitropic response in the primary root that causes it to grow down into the soil, providing support and nutrient acquisition. Gravity also influences plant form during later stages of development through its effect on lateral organs and supporting structures. Thus, the final form of a plant depends on the cumulative effects of light, gravity and other environmental sensory inputs on endogenous developmental programs. This article is focused on developmental interactions modulated by light and gravity.

Molecular genetic analysis of plant gravitropism

The analysis of mutants is a powerful approach for elucidating the components of complex biological processes. A growing number of mutants have been isolated which affect plant gravitropism and the classes of mutants found thus far provide important information about the gravity response mechanism. The wide variety of mutants isolated, especially in Arabidopsis, indicates that gravitropism is a complex, multi-step process. The existence of mutants altered in either root gravitropism alone, shoot gravitropism alone, or both indicates that the root and shoot gravitropic mechanisms have both separate and common steps. Reduced starch mutants have confirmed the role of amyloplasts in sensing the gravity signal. The hormone auxin is thought to act as the transducing signal between the sites of gravity perception (the starch parenchyma cells surrounding the vascular tissue in shoots and the columella cells of root caps) and asymmetric growth (the epidermal cells of the elongation zone(s) of each organ). To date, all mutants that are resistant to high concentrations of auxin have also been found to exhibit a reduced gravitropic response, thus supporting the role of auxin. Not all gravitropic mutants are auxin-resistant, however, indicating that there are additional steps which do not involve auxin. Studies with mutants of tomato which exhibit either reduced or reversed gravitropic responses further support the role of auxin redistribution in gravitropism and suggest that both red light and cytokinin interact with gravitropism through controlling lateral auxin transport. Plant responses to gravity thus likely involve changes in both auxin transport and sensitivity.

Respirometer for small samples with automatic registration

The respiration chamber containing the sample is a small glass test tube with a closure of KOH solution. During registration the gas volume is kept constant by adjusting the pressure through a feedback mechanism: a microscope projects the picture of the meniscus of KOH onto a photodiode connected to a pen recorder with a vertically moving pen. A levelling bulb with water mounted on the pen transmits the pressure adjustments to the KOH solution through a water filled tubing. The accuracy is +/-0.1 mm water column (1 Pa) and the minimum air volume is 10 nl, so that an oxygen consumption down to 1 pl can be seen.

Expression of a betaine aldehyde dehydrogenase gene in rice, a glycinebetaine nonaccumulator, and possible localization of its protein in peroxisomes

Betaine aldehyde dehydrogenase (BADH) catalyzes the last step in the plant biosynthetic pathway that leads to glycinebetaine. Rice plants (Oryza sativa L.), albeit considered a typical non-glycinebetaine accumulating species, have been found to express this enzyme at low levels. This observation evokes an interest in phylogenic evolution of the enzyme in the plant kingdom. It is reported here that rice plants possess the ability to take up exogenously added betaine aldehyde through the roots and convert it to glycinebetaine, resulting in an enhanced salt-tolerance of the plants. A gene encoding a putative BADH from the rice genome was also cloned and sequenced. The gene was found to contain 14 introns, and the overall nucleotide sequence of the coding region is c. 78% identical to that of the barley BADH cDNA. Cloning of a partial BADH cDNA from rice was accomplished by reverse transcription-polymerase chain reaction (RT-PCR). The nucleotide sequence of the cloned fragment was found to be identical to the corresponding exon regions of the rice genomic BADH gene. The deduced amino acid sequences of rice and barley BADH both contain a C-terminal tripeptide SKL, a signal known to target preproteins to microbodies. This localization was confirmed by an immuno-gold labeling study of transgenic tobacco harboring barley cDNA, which showed BADH protein inside peroxisomes. Northern blot analysis revealed that the level of BADH mRNA is salt-inducible.

A novel gene whose expression in Medicago truncatula roots is suppressed in response to colonization by vesicular-arbuscular mycorrhizal (VAM) fungi and to phosphate nutrition

A cDNA clone (Mt4) was isolated as a result of a differential screen to identify genes showing altered expression during the interaction between Medicago truncatula and the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus versiforme. Mt4 represents a M. truncatula mRNA that contains numerous short open reading frames, the two longest of which are predicted to encode polypeptides of 51 amino acids each. One of these open reading frames shares a short region of identity with a phosphate starvation-inducible gene from tomato. Mt4 gene expression is regulated in response to colonization by mycorrhizal fungi: transcripts were detected in non-colonized roots and levels decreased in both M. truncatula and M. sativa (alfalfa) roots after colonization by G. versiforme. Transcript levels also decreased during the incomplete interaction between G. versiforme and a M. sativa mycorrhizal minus (myc-) line, indicating that the down-regulation of this gene occurs early during the interaction between the fungus and its host plant. Phosphate levels in the nutrient media also affected the expression of the Mt4 gene: transcripts were present in the roots of plants grown under phosphate-deficient conditions, but were undetectable in the roots of plants grown under phosphate sufficient conditions. Furthermore, expression was only observed when plants were grown under nitrogen-sufficient conditions. Northern blot analyses indicate that Mt4 transcripts are present primarily in roots and barely detectable in stems or leaves. Thus, Mt4 represents a M. truncatula gene whose expression is regulated in response to both colonization by mycorrhizal fungi and to the phosphate status of the plant.

Expression of a betaine aldehyde dehydrogenase gene in rice, a glycinebetaine nonaccumulator, and possible localization of its protein in peroxisomes

Betaine aldehyde dehydrogenase (BADH) catalyzes the last step in the plant biosynthetic pathway that leads to glycinebetaine. Rice plants (Oryza sativa L.), albeit considered a typical non-glycinebetaine accumulating species, have been found to express this enzyme at low levels. This observation evokes an interest in phylogenic evolution of the enzyme in the plant kingdom. It is reported here that rice plants possess the ability to take up exogenously added betaine aldehyde through the roots and convert it to glycinebetaine, resulting in an enhanced salt-tolerance of the plants. A gene encoding a putative BADH from the rice genome was also cloned and sequenced. The gene was found to contain 14 introns, and the overall nucleotide sequence of the coding region is c. 78% identical to that of the barley BADH cDNA. Cloning of a partial BADH cDNA from rice was accomplished by reverse transcription-polymerase chain reaction (RT-PCR). The nucleotide sequence of the cloned fragment was found to be identical to the corresponding exon regions of the rice genomic BADH gene. The deduced amino acid sequences of rice and barley BADH both contain a C-terminal tripeptide SKL, a signal known to target preproteins to microbodies. This localization was confirmed by an immuno-gold labeling study of transgenic tobacco harboring barley cDNA, which showed BADH protein inside peroxisomes. Northern blot analysis revealed that the level of BADH mRNA is salt-inducible.

In vitro study of passive nitrate transport by native and reconstituted plasma membrane vesicles from corn root cells

Proteins from phase-partitioned corn root plasma membrane were reconstituted into soybean lipids/egg PC (8:2, w:w) using deoxycholate and rapid gel filtration to eliminate the detergent. All (H+)ATPase molecules were inside-out reinserted and the initial activity was totally recovered in an homogeneous vesicle preparation. In addition, membrane tightness greatly increased, as shown by the size and stability of the response of the fluorescent membrane potential probe (oxonol VI) to an imposed K+ diffusion gradient. Consequently, the H(+)-pumping activity of the (H+)ATPase, monitored with the fluorescent pH probe (ACMA), increased 20-fold after reconstitution. A protein-mediated passive transport of nitrate was first demonstrated by the ability of NO3- to electrically short-circuit the (H+)ATPase in plasma membrane vesicles and not in liposomes containing only the purified enzyme. The passive transport was saturable (K(m) approximately 5 mM), thermolabile, inhibited by the arginine reagent phenylglyoxal, and selective (NO3- > I- approximately ClO3- approximately Br- > Cl- approximately NO2- > Iminodiacetate approximately SO4(2-)). Passive NO3- transport was also determined, independently of the (H+)ATPase, from the NO3(-)-dependent augmentation of the dissipation rate of imposed diffusion potentials. This second transport assay gave similar K(m) for NO3- and should be suitable to continue the functional and biochemical characterization of the NO3- transport system.

Effect of low oxygen concentration on the electrical properties of cortical cells of wheat roots

Short-term effect of oxygen-deficiency on the membrane potential difference (PD), membrane resistance of cortical cells and electrical coupling between cortical cells was investigated using excised wheat roots. Hypoxia rapidly depolarised the membrane potential of the cortical cells by about 60 mV, while hypoxia had little effect on the membrane resistance of the cells. No significant change in membrane resistance by potassium channel blockers, TEA+ and verapamil, under hypoxia was observed. The electrical coupling ratio, which is a measure of plasmodesmatal resistance, between cortical cells of wheat roots was 5.9 % in aerated solution and was not affected by the low oxygen treatment, suggesting that solute transport through cytoplasmic annulus of plasmodesmata could not be affected. The possible involvement of the endoplasmic reticulum in intercellular transport of solute and water is discussed.

Continual green-fluorescent protein monitoring of cauliflower mosaic virus 35S promoter activity in nematode-induced feeding cells in Arabidopsis thaliana

The responsiveness of the cauliflower mosaic virus 35S promoter in feeding sites developed by both sexes of Heterodera schachtii and female Meloidogyne incognita has been studied. The objective was to establish the value of green-fluorescent protein (GFP) as a nondestructive reporter gene system for characterizing promoter activity at nematode feeding sites in vivo. Growth units were devised that allowed individual feeding sites in roots of Arabidopsis thaliana to be observed by both bright-field and epifluorescent illumination. Changes in GFP expression were visually observed under experimental conditions that resulted in chloroplast formation in syncytia but not other root cells. Changes in GFP levels altered the extent of quenching, by this protein, of red light emitted by chlorophyll within the chloroplasts under violet excitation. Image analysis provided a semiquantitative basis for simultaneous measurement of changes in GFP fluorescence and the unquenched emission by chlorophyll. GFP levels were constant in cells surrounding the syncytium induced by H. schachtii, but they fell progressive from 10 to 35 days postinfection within this structure. Significant reduction in GFP levels was not limited to the early part of the time course but also occurred between 27 and 35 days postinfection. GFP was detected by immunoblotting in females of M. incognita but not in H. schachtii parasitizing similar GFP-expressing roots.

Induction of chalcone synthase expression by rhizobia and nod factors in root hairs and roots

Chalcone synthase (CHS) of Vigna unguiculata is encoded by a gene family that is abundantly transcribed in leaves and nodules. Inoculation with Rhizobium sp. NGR234, which nodulates V. unguiculata, or with NGR delta nodABC, a mutant deficient in Nod factor production, induced rapid accumulation of CHS mRNAs in roots and root hairs. As both Nod+ and Nod- bacteria provoke responses, induction of CHS gene expression may involve symbiotic or defense responses. Four days after inoculation with the wild-type Rhizobium sp., the transcript levels increased in roots but decreased in root hairs. Use of a region unique to the 5' end of a specific CHS gene (VuCHS1) showed that increases of transcript levels in root hairs 24 h after inoculation with both rhizobia were specific to this gene. Transcripts of this gene in roots were only detectable 4 days after treatment with NGR234. It is possible therefore that accumulation of VuCHS1 follows the infection pathway of rhizobia entering legume roots. Purified Nod factors induced accumulation of transcripts, showing that they might be part of the signal transduction pathway leading to CHS expression.

Characterization of recombinant soybean leghemoglobin a and apolar distal histidine mutants

The cDNA for soybean leghemoglobin a (Lba) was cloned from a root nodule cDNA library and expressed in Escherichia coli. The crystal structure of the ferric acetate complex of recombinant wild-type Lba was determined at a resolution of 2.2 A. Rate constants for O2, CO and NO binding to recombinant Lba are identical with those of native soybean Lba. Rate constants for hemin dissociation and auto-oxidation of wild-type Lba were compared with those of sperm whale myoglobin. At 37 degrees C and pH 7, soybean Lba is much less stable than sperm whale myoglobin due both to a fourfold higher rate of auto-oxidation and to a approximately 600-fold lower affinity for hemin. The role of His61(E7) in regulating oxygen binding was examined by site-directed mutagenesis. Replacement of His(E7) with Ala, Val or Leu causes little change in the equilibrium constant for O2 binding to soybean Lba, whereas the same mutations in sperm whale myoglobin cause 50 to 100-fold decreases in K(O2). These results show that, at neutral pH, hydrogen bonding with His(E7) is much less important in regulating O2 binding to the soybean protein. The His(E7) to Phe mutation does cause a significant decrease in K(O2) for Lba, apparently due to steric hindrance of the bound ligand. The rate constants for O2 dissociation from wild-type and native Lba decrease significantly with decreasing pH. In contrast, the O2 dissociation rate constants for mutants with apolar E7 residues are independent of pH, suggesting that hydrogen bonding to the distal histidine residue in the native protein is enhanced under acid conditions. All of these results support the hypothesis that the high affinity of Lba for oxygen and other ligands is determined primarily by enhanced accessibility and reactivity of the heme group.

Mist deposition onto hairy root cultures: aerosol modeling and experiments

We analyzed the applicability of the standard models for aerosol deposition in randomly packed fibrous filter beds to mist deposition across a bed of hairy roots in the nutrient mist bioreactor. Although the assumptions inherent in the models are met on a local level, the overall structure of the root bed introduces some uncertainty into the correct choice of root packing fraction and gas velocity required by the model. For reasonable parameter values, the minimum in the deposition efficiency curves is close to the peak in the mist number and mass distributions, and good penetration of the root bed is possible. We then measured the deposition of mist across a packed bed of Artemisia annua transformed roots as a function of droplet size, bed length, and gas flow rate at a root packing fraction alpha = 0.5. We compared the experimental measurements with the predictions of the aerosol deposition model and found good agreement between the measured and predicted values for the diameter where the deposition efficiency across the bed is 50%, D0.5. Agreement between the model and the experiments broke down when the flow rate was increased to the point where the creeping flow assumptions were no longer valid.

A novel glycine-rich/hydrophobic 16 kDa polypeptide gene from tobacco: similarity to proline-rich protein genes and its wound-inducible and developmentally regulated expression

We have isolated a cDNA clone, NT16, encoding a novel glycine-rich/hydrophobic protein from tobacco crown gall tumor tissues, which was induced by the T-DNA genes of Agrobacterium tumefaciens. The accumulation of NT16 transcripts was high in unorganized callus as well as in shoot-forming calli. In normal tobacco plants, the transcript levels were high in roots, and low in stems, whereas virtually no transcript accumulation was found in flowers or leaves. In leaves, however, NT16 transcript accumulation was induced by mechanical wounding. These results show that NT16 expression is developmentally regulated and induced by wound-stress conditions. Sequence analysis suggests that NT16 encodes a putative 16 kDa polypeptide that is apparently composed of 3 structural domains: two hydrophobic regions separated by a glycine-rich region. The NT16 polypeptide displays similarity to a number of proteins in its hydrophobic domains, but is unique in its glycine-rich domain which, in the corresponding domains of the homologous proteins, are mostly proline-rich. Since both glycine-rich and proline-rich proteins are generally reported to be mostly cell wall proteins, the NT16 gene may be involved in shoot and root formation and in wound-healing process by modifying cell wall composition.

[Phosphoric stress and antioxidative power of wheat roots]

The change of antioxydative power of metabolites in the wheat root system (cv Polesskaya 90 and cv Polesskaya 92) under effect of stress doses of phosphoric nutrition (4-fold dose and phosphoric deficit in nutrient mixture of water culture) proves that phosphoric stress causes peroxidation of membrane lipids. These changes are a nonspecific reaction of membranes in root epithelial cells. Stress and responsive changes in the membrane system are recorded by an antioxydative power decreasing root metabolites. This is the first stage of plant biochemical adaptation (7 to 14 days of growth). The second stage (21 to 28 days of growth) is characterised by the increasing of antioxydative power. However, nonspecific character of the primary reaction of membrane system in root cells at high doses and phosphoric deficite in nutrient mixture changes into clear specific reaction at physiological adaptation level. This is revealed in the change of growth function and kinetics of phosphoric accumulation. Phosphoric deficiency at critical phosphoric concentration in plant roots (0.2% P2O5 of dry mass) results in the increase of growth processes. This is revealed in accumulation of root biomass. At high phosphoric concentrations (1.04% P2O3) the development of root system is inactivated and phosphoric absorption is decreased. The similar specificity in the changes of growth and absorption function of root system is considered to be adapting. The changes of antioxydative power and hence the destroying apparatus in epithelial cells of root system advance the damage at physiological and morphological level and can define wheat adaptation ability to extreme conditions of phosphoric nutrition.

The role of liquid mixing and gas-phase dispersion in a submerged, sparged root reactor

An Agrobacterium-transformed root culture of Solanum tuberosum was grown in a 15-1 bubble column. The specific respiration rate decreased by a factor of ten as the tissue grew over a 25-day culture period. On days 5, 8, 13, and 21, respiration was shown to be independent of aeration rate over a range of 0.05-0.4 vvm (volume of air per volume of liquid min-1). Gas dispersion measured from argon tracer residence time distributions increased fourfold due to increased stagnation and channeling of gas through the bed of growing roots; however, introduction of an antifoam surfactant on day 20 greatly reduced dispersion with no accompanying change in respiration. Taken together, the gas dispersion and respiration studies suggest that the gas-liquid interface is not the dominant resistance to oxygen mass transfer. Liquid mixing time measured with a dye tracer increased from 1.45 +/- 0.45 min with no root tissue to 40.2 +/- 1.6 min with 180 g FW l-1 of roots in the column. In addition, the oxygen uptake rate of growing tips (5.2 +/- 0.2 mm) of individual root segments of S. tuberosum measured in a stirred microcell (600 microliters) increased with the oxygen tension of the medium. Based on these results, the role of liquid mixing, gas-phase dispersion, and diffusion in the tissue in the scaleup of root culture is discussed.

Chilling stress leads to increased cell membrane rigidity in roots of coffee (Coffea arabica L.) seedlings

Tropical and sub-tropical higher plant species show marked growth inhibition when exposed to chilling temperatures. In root tip segments of coffee seedlings which were subjected for 6 days to temperatures of 10, 15, 20 and 25 degrees C, in darkness, we have detected an increased amount of malondialdehyde formed in the 10 degrees C treatment, accompanied by higher electrolyte leakage. The electron paramagnetic resonance (EPR) technique and the fatty acid spin probes 5-, 12- and 16-doxylstearic acid were used to assess cellular membrane fluidity. At the depth of the 5th and 16th carbon atom of the alkyl chains the nitroxide radical detected more rigid membranes in seedlings subjected to 10 degrees C compared with 15 and 25 degrees C. At the C-12 position of the chains the probe showed very restricted motion and was insensitive to chilling induced membrane alterations. EPR parameters for intact tissues and microsome preparations from root tips showed that the fluidity was essentially the same when evaluated at C-5 and C-16 positions of the chains, and was considerably more fluid for microsomal membranes in the region of the C-12 position of the bilayers. The rotational motion of the nitroxide at C-16 position of the chains experienced a phase transition at about 15 degrees C. The calculated energy barriers for reorientational motion of the probe 16-doxylstearic acid were higher at temperatures of 5-15 degrees C than in the interval of 15-25 degrees C, suggesting that below the phase transition the membrane lipids assume a more ordered and compacted array. Membrane rigidity induced by chilling was interpreted as due to lipid peroxidation that could have been facilitated by higher density of peroxidizable chains below the membrane phase transition.

Fructan synthesis in transgenic tobacco and chicory plants expressing barley sucrose: fructan 6-fructosyltransferase

We have recently cloned a cDNA encoding sucrose:fructan 6-fructosyltransferase (6-SFT), a key enzyme of fructan synthesis forming the beta-2,6 linkages typical of the grass fructans, graminans and phleins [Sprenger et al. (1995) Proc. Natl. Acad. Sci. USA 92, 11652-11656]. Here we report functional expression of 6-SFT from barley in transgenic tobacco and chicory. Transformants of tobacco, a plant naturally unable to form fructans, synthesized the trisaccharide kestose and a series of unbranched fructans of the phlein type (beta-2,6 linkages). Transformants of chicory, a plant naturally producing only unbranched fructans of the inulin type (beta-2,1 linkages), synthesized in addition branched fructans of the graminan type, particularly the tetrasaccharide bifurcose which is also a main fructan in barley leaves.

Identification of mutants in metabolically regulated gene expression

Sucrose is the main transported form of assimilates, but, significantly, it also regulates a variety of processes such as photosynthesis and carbon or nitrogen storage. The effects of high sucrose levels are mediated directly by modulation of gene expression. The regulation of storage protein accumulation, here patatin from potato tubers, was used as a model system to study sucrose mediated signal transduction. The transcriptional regulation of patatin genes in conserved in transgenic Arabidopsis, as shown by the analysis of expression of two classes of patatin promoters fused to uidA. Two distinctly different patterns of gene expression were observed. In roots, class I promoter expression is strongly dependent on the exogenous supply of sugars. 3-O-methylglucose induction indicates that the sensor is located upstream of hexokinase. In contrast, the class II promoter is constitutively active in root tips and hydatodes. The progeny of a homozygous class I line was mutagenized with ethyl methane sulphonate and screened for signal transduction mutants using a non-destructive screening system for GUS activity. Four mutants showing reduced sucrose responses (rsr) and two mutants with modified expression patterns (mep) regarding the root tip were identified. In backcross analyses, it was shown that rsr1-1 carries a recessive trans mutation whereas rsr4-1 seems to be a semi-dominant trans mutation in sugar-mediated gene regulation.

Use of biologically reclaimed minerals for continuous hydroponic potato production in a CELSS

Plant-derived nutrients were successfully recycled in a Controlled Ecological Life Support System (CELSS) using biological methods. The majority of the essential nutrients were recovered by microbiologically treating the plant biomass in an aerobic bioreactor. Liquid effluent containing the nutrients was then returned to the biomass production component via a recirculating hydroponic system. Potato (Solanum tuberosum L.) cv. Norland plants were grown on those nutrients in either a batch production mode (same age plants on a nutrient solution) or a staggered production mode (4 different ages of plants on a nutrient solution). The study continued over a period of 418 days, within NASA Breadboard Project's Biomass Production Chamber at the Kennedy Space Center. During this period, four consecutive batch cycles (104-day harvests) and 13 consecutive staggered cycles (26-day harvests) were completed using reclaimed minerals and compared to plants grown with standard nutrient solutions. All nutrient solutions were continually recirculated during the entire 418 day study. In general, tuber yields with reclaimed minerals were within 10% of control solutions. Contaminants, such as sodium and recalcitrant organics tended to increase over time in solutions containing reclaimed minerals, however tuber composition was comparable to tubers grown in the control solutions.

Flow cytometry, sorting and immunocharacterization with proliferating cell nuclear antigen of cycling and non-cycling cells in synchronized pea root tips

In the 3-d-old 2-mm root tip of Pisum sativum L. cv. Lincoln the percentage of actively proliferating cells is estimated to be 70%. The remaining cells are non-cycling and arrested with 2C and 4C DNA content in G0 and in G2Q, respectively. In this work we studied the kinetic significance of these quiescent cells, using the sorting capabilities of flow cytometry and immunofluorescence techniques to detect the proliferation marker PCNA (proliferating cell nuclear antigen) inside cells within the different cell-cycle compartments. While in animal cells, PCNA is present at a high level only in actively proliferating cells, in 3-d-old pea root tips 95% of the cells are PCNA-positive. After flow cytometry and sorting of pea non-cycling nuclear populations, all G2Q nuclei appeared strongly PCNA-positive, indicating that these cells had recently left the cell cycle. By contrast, most G0 nuclei showed a low level of PCNA immunofluorescence intensity, as measured by image analysis, with about 25% of the nuclei being PCNA-negative. This small percentage was found to correspond to root cap cells, as could be observed in the root tip section. These are the only cells in the root apical region which are fully differentiated and which, therefore, lack the competence to enter the cell cycle. In contrast, the more or less PCNA-positive G0 nuclei could represent a kinetically heterogeneous population of cells competent to proliferate, but which have either recently left the cell cycle or are progressing to the G0-G1 transition.

Effect of calcium on RNA content in meristematic cells of pea (Pisum sativum L.) roots treated with toxic metals

RNA content in nucleolus, nucleus and cytoplasm in meristematic cells of pea roots growing for 144 h in the presence of calcium and/or toxic metals (Cd2+, Cr3+, Pb2+) was examined using cytophotometric procedures, after staining with gallocyanine. The effect of treatment with tested metals was twofold: on the one hand, it considerably reduced RNA content in the nucleolus, on the other it enhanced RNA level in the nucleus and most visibly in the cytoplasm, resulting in the increase in total amount of RNA in cells of pea roots. The presence of calcium in metal solutions in different ways affected RNA content in meristematic cells of pea. In roots treated with cadmium, the addition of calcium ions diminished the toxic effect of that metal, as demonstrated by an increase in RNA content in the nucleolus, although reduction of RNA amount in the nucleus, cytoplasm and in whole cell was observed. A clearly stimulative effect of calcium was noted in material grown in the presence of chromium or lead, where a high increase in RNA content in nucleolus, nucleus and cytoplasm took place.

CO2 enrichment influences yields of 'Florunner,' 'Georgia Red' and 'New Mexico' peanut cultivars

Three peanut cultivars, 'Florunner,' 'Georgia Red,' and 'New Mexico,' were grown in reach-in chambers to determine response to CO2 enrichment. CO2 treatments were ambient (400 micromol mol-1) and 700 micromol mol-1. Growth chamber conditions included 700 micromol m-2 s-1 photosynthetic photon flux (PPF), 28/22C, 7O% RH, and 12/12 h photoperiod. Growth media consisted of a 1:1 mixture (v/v) of vermiculite and sterilized sand. Six 10 L pots of each cultivar were fertilized three times per week with 250 mL of nutrient solution containing additional Ca (10 mM) and NO3 (25 mM) and watered well. Beginning 21 days after planting (DAP) and every three weeks thereafter up to 84 days, the second leaf from the growing axis (main stem) was detached to determine CO2 effect on leaf area, specific leaf area (SLA) and dry weight. Plants were harvested 97 DAP, at which time total leaf area, leaf number, plant and root weights and pod production data were taken. Numbers of pods per plant, pod fresh and dry weights, fibrous root and plant dry weights were higher for all cultivars grown at 700 micromol mol-1 than at ambient CO2. Also, leaf area for all cultivars was larger with CO2 enrichment than at ambient. SLA tended to decline with time regardless of CO2 treatment. Percentage of total sound mature kernels (%TSMK) was similar for both treatments. Plants grown at 700 micromol mol-1 CO2 had slightly more immature pods and seeds at final harvest.