Foaming and cell flotation in suspended plant cell cultures and the effect of chemical antifoams

Foam development and stability in Atropa belladonna suspensions were investigated as a function of culture conditions. Foaming was due mainly to properties of the cell-free broth and was correlated with protein content; effects due to presence of cells increased towards the end of batch culture. Highest foam levels were measured 11 days after inoculation. Air flow rate was of major importance in determining foam volume; foam volume and stability were also strongly dependent on pH. Foam flotation of plant cells was very effective. After 30 min foaming, ca. 55% of cells were found in the foam; this increased to ca. 75% after 90 min. Polypropylene glycol 1025 and 2025, Pluronic PE 6100, and Antifoam-C emulsion were tested as chemical antifoams. Polypropylene glycol 1025 and Antifoam C at concentrations up to 600 ppm had no adverse effect on growth in shake flasks; Pluronic PE 6100 has an inhibitory effect at all levels tested. Concentrations of polypropylene glycol 2025 and Pluronic PE 6100 as low as 20 ppm reduced foam volumes by a factor of ca. 10. Addition of antifoam reduced k(L)a values in bubble-column and stirred-tank bioreactors. After operation of a stirred reactor for 2 days using Antifoam C for foam control, cell production was limited by oxygen due to the effect of antifoam on mass transfer. Theoretical analysis showed that maximum cell concentrations and biomass levels decline with increasing reactors working volume due to greater consumption of antifoam to prevent foam overflow. The results indicate that when chemical foam control is used in plant cell cultures, head-space volume and tolerable foam levels must be considered to optimize biomass production. (c) 1994 John Wiley & Sons, Inc.     

Hopped Beer: The Case For Cultivation

The history of hops, hopped beer, and hop cultivation is unclear and ambiguous. An assessment of the available literature reveals many contradictions, especially regarding the first use of hops in beer and the earliest incidence of hop cultivation. Historically, hops were used for a variety of purposes; now their primary use is as a preservative and flavoring in beer. Hop cultivation is poorly documented, but was certainly undertaken by the 10th century, most probably in response to the demand generated by beer-brewing. After comparing the literature and investigating source material, a chronology of hop use in beer and hop cultivation is proposed.     

Effects of genetic and environmental host plant variation on the susceptibility of two noctuids toBacillus thuringiensis

TwoApium graveolens var.rapaceum (L.) cultivars that differ in their suitability for the survival and growth ofSpodoptera exigua (Hübner) andTrichoplusia ni (Hübner) were used to examine the effect of genetic and seasonal environmental variation in host plant suitability on the efficacy ofBacillus thuringiensis subsp.kurstaki (Berliner). The effects of host plant genotype andB. thuringiensis were generally independent, so thatB. thuringiensis efficacy was greatest on the resistant host plant cultivar. Host plant suitability varied within growing season for both insect species but, while host plant suitability decreased with increasing plant age forT. ni, the response ofS. exigua to plant age was not as clear. Within season variation in host plant suitability affectedB. thuringiensis efficacy and the interaction betweenB. thuringiensis and host plant cultivar forS. exigua but not forT. ni. Soluble protein and Folin-Denis phenolic concentrations of host plant tissue were not correlated with changes in host plant suitability to either insect species.     

Insects and fungi on a C3 sedge and a C4 grass exposed to elevated atmospheric CO2 concentrations in open-top chambers in the field

The effects of elevated atmospheric CO₂ concentration on plant-fungi and plant-insect interactions were studied in an emergent marsh in the Chesapeake Bay. Stands of the C₃ sedge Scirpus olneyi Grey, and the C₄ grass Spartina patens (Ait.) Muhl. have been exposed to elevated atmospheric CO₂ concentrations during each growing season since 1987. In August 1991 the severities of fungal infections and insect infestations were quantified. Shoot nitrogen concentration ([N]) and water content (WC) were determined. In elevated concentrations of atmospheric CO₂, 32% fewer S. olneyi plants were infested by insects, and there was a 37% reduction in the severity of a pathogenic fungal infection, compared with plants grown in ambient CO₂ concentrations. S. olneyi also had reduced [N], which correlated positively with the severities of fungal infections and insect infestations. Conversely, S. patens had increased WC but unchanged [N] in elevated concentrations of atmospheric CO₂ and the severity of fungal infection increased. Elevated atmospheric CO₂ concentration increased or decreased the severity of fungal infection depending on at least two interacting factors, [N] and WC; but it did not change the number of plants that were infected with fungi. In contrast, the major results for insects were that the number of plants infected with insects decreased, and that the amount of tissue that each insect ate also decreased.     

Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization

Ambient atmospheric CO₂ concentration ([CO₂]_a) has apparently declined from values above 200μmol mol⁻¹ to values below 200μmol mol⁻¹ within the last several million years. The lower end of this range is marginal for C₃ plants. I hypothesize that: (1) declining [CO₂]_a imposed a physiological strain on plants, and plant taxa evolving under declining [CO₂]_a tended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO₂]_a than were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast-evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO₂ starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.     

A new,pathogen-inducible gene of Arabidopsis is expressed in an ecotype-specific manner

In this study we describe a novel gene, which was isolated in an attempt to search for specific plant resistance genes of Arabidopsis against isolates of the phytopathogenic bacterium Xanthomonas campestris pv. campestris. The gene was cloned by differential screening of a genomic library of the Xcc 750-resistant ecotype Col-0, using cDNA populations derived from ecotype Col-0 and the Xcc 750-susceptible ecotype Oy-0. The isolated gene, CXc750, is differentially expressed in ecotypes of Arabidopsis thaliana. In addition, although highly expressed in uninfected plants, gene expression increases in response to pathogen attack. CXc750 potentially codes for a small, basic protein of about 10 kDa. The predicted protein product contains a potential signal leader peptide at the amino-terminal end but no ER retention sequence and no further transmembrane domain. This indicates that the gene product is transported to other compartments or out of the cell.The possible function of CXc750 as a member of the plant defense response system is discussed.     

Polymeric derivatives of plant growth regulators: synthesis and properties

The polymeric formulations of plant growth regulators (PGRs) are high molecular weight systems in which the PGR unit is attached to the polymeric chain by a hydrolysable chemical bond. These polymeric derivatives (esters, ethers, or else) of PGRs are characterised by the ability to release the active compound (PGR) from their solutions (mainly aqueous) in certain conditions. The release of the PGR can be controlled by external factors (pH, temperature, enzymes, solution concentration), and inherent properties of the whole macrosystem chemical structure, such as the type of the hydrolysable bond between PGR unit and the main polymeric chain, the structure of the polymer chain (e.g. molecular weight, level of hydrophilicity, and the content of hydrophobic groups, macromolecular conformation in solution etc.). These controlled (slow) release PGRs display certain advantages over conventional PGR formulations due to their prolonged action, improved efficiency (e.g. wide range of effective concentrations) greater safety to non-target organisms and the applicators. In addition the ability of altering the solubility level and modifying the aplication form is of considerable interest. The biological activity efficiency of polymeric PGRs has been documented and the relation of this efficiency to the PGR unit hydrolytic release ability has been mentioned. Slow release polymeric PGRs are considered to solve certain problems in agriculture.Abbreviations PGR plant growth regulator - C(S)RF controlled (slow) release form - PD polymeric derivative - ACC 1-amino-cyclopropane-1-carboxylic acid - NAA 1-naphthylacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - BAP N⁶-benzylaminopurine - ABA abscisic acid - GA gibberellin - LMW low molecular weight - HMW high molecular weight     

A simple classification of the complex parts of vascular plants

Four operational morphological units are defined to characterize 'typical' stems, leaves, roots and hairS. Any complex part can be classified among these OMUs by a graphical representation or by a quadruplet suitable for computer-aided analyses. Thirty-nine examples are given, suggesting a continuous view of plant morphology.     

Integrated nitrogen,carbon, and water relations of a xylem-tapping mistletoe following nitrogen fertilization of the host

Xylem-tapping mistletoes transpire large volumes of water (E) while conducting photosynthesis (A) at low rates, thus maintaining low instantaneous wateruse efficiency (A/E). These gas-exchange characteristics have been interpreted as a means of facilitating assimilation of nitrogen dissolved at low concentration in host xylem water; however, low A/E also results in substantial heterotrophic carbon gain. In this study, host trees (Juniperus osteosperma) were fertilized and gas exchange of mistletoe (Phoradendron juniperinum) and host were monitored to determine whether mistletoe A/E would approach that of the host if mistletoes were supplied with abundant nitrogen. Fertilization significantly increased foliar N concentrations (N), net assimilation rates, and A/E in both mistletoe and host. However, at any given N concentration, mistletoes maintained lower A and lower A/E than their hosts. On the other hand, when instantaneous water-use efficiency and A/N were calculated to include heterotrophic assimilation of carbon dissolved in the xylem sap of the host, both water-use efficiency and A/N converged on host values. A simple model of Phoradendron carbon and nitrogen budgets was constructed to analyze the relative benefits of nitrogen- and carbonparasitism. The model assumes constant E and includes feedbacks of tissue nitrogen concentration on photosyn-thesis. These results, combined with our earlier observation that net assimilation rates of mistletoes and their hosts are approximately matched (Marshall et al. 1994), support part of the nitrogen-parasitism hypothesis: that high rates of transpiration benefit the mistletoe primarily through nitrogen gain. However, the low ratio of A/E is interpreted not as a means of acquiring nitrogen, but as an inevitable consequence of an imbalance in C and N assimilation.This research was supported by the National Science Foundation (grants BSR-8706772 and 8847942).