Cell cultures vs. whole plants for measuring phytotoxicity II. Correlations between phytotoxicity in seedlings and calli

The effects of a broad range of compounds were assessed usingboth seedlings and callus cultures of five species. An experimentallyjustified ranking procedure was used to facilitate the comparisonof the inhibitory characteristics at multiple concentrations.When the effects on seedlings of Lycopersicon esculentum, Solanumnigrum, Chrysanthemum segetum and Cirsium arvense were comparedto those on white calli of the same species, some positive correlationswere obtained; photosynthesis inhibitors affected seedlingsmuch more than calli and some compounds affected calli muchmore than seedlings. Better correlations were obtained betweenthe effects on Rumex obtusifolius seedlings and on green Rumexcalli; the only exceptions being those compounds affecting mainlythe calli. Thus callus cultures, especially green ones, havea potential for use to assess possible phytotoxicity as wellas to detect potential toxicity of compounds not penetratinginto or being translocated in whole plants. (Received January 13, 1977; )     

The determination of chlorophylls a and b together with 14CO2 fixation in the same plant tissue samples

A simple, efficient, and inexpensive method for measuring radioactivity as well as chlorophylls a and b in a large number of plant tissue samples is presented. Chlorophyll is determined following extraction with dimethyl sulfoxide or N-N'-dimethylformamide. The solvent is then evaporated on glass-fiber filters and bleached under light. The filter disks are counted together with the cleared plant material.     

Thermal denaturation of nucleic acids in polyacrylamide gels

A system is described for measuring thermal denaturation of nucleic acid fractions directly in polyacrylamide gels. Total nucleic acids were fractionated by disc gel electrophoresis. The buffer within the gel was then exchanged for one commonly used in denaturation studies. Thermal denaturation profiles of DNA and ribosomal RNA in the gel were determined using a specially constructed Gel Carriage to position the appropriate fraction during spectrophotometric measurements. These profiles were compared with denaturation patterns obtained by classical methods in free solution; the two methods yielded similar patterns.Thermal denaturation profiles were also obtained for chloroplast light ribosomal RNA resolved by gel electrophoresis of total plant nucleic acids. Thus, denaturation patterns of individual, minor components present in complex nucleic acid mixtures can be directly measured in gels.     

Electric Currents around Growing Trichoderma Hyphae, before and after Photoinduction of Conidiation

Electric currents were measured around Trichoderma harzianum (Rifai) hyphae using an extracellular vibrating electrode. A steady current enters growing hyphal tips and along the side of the apical millimeter. In addition, outward currents were detected at about one-ninth of the locations tested, 60 to 150 minutes after illumination but not in dark controls. This sporadic, localized outward current pattern might be an early biophysical response to blue light.     

Cell suspensions for kinetic studies of inhibitor action

Because of uniformity and small distances for transport, cell suspensions offer a system for rapid measurements of initial reactions of phytotoxic compounds. We had previously shown that a growth regulator, dikegulac (2,3:4,6 di-o-isopropylidine-2-keto-L-gulonate) inhibits amino acid incorporation into proteins. Using Solanum nigrum suspension cultures, it was found that dikegulac rapidly inhibits amino acid uptake into cells, before inhibiting incorporation, with time points starting at a few minutes, and kinetics that can be extrapolated back to time zero. With more rapid kinetics this compound induces leakage of a preloaded dye. The rate of leakage was less with stationary cells in suspension, reiterating that they are more resistant to the effects of this compound. It was thus concluded that at the concentrations used, the first effect of dikegulac (or one very close to the first effect) is on the cell membrane.Abbreviation FDA fluorescein diacetate     

Tandem constructs: preventing the rise of superweeds.

Transgenic crops may interbreed with nearby weeds, increasing their competitiveness, and may themselves become a 'volunteer' weed in the following crop. The desired transgene can be coupled in tandem with genes that would render hybrid offspring or volunteer weeds less able to compete with crops, weeds and wild species. Genes that prevent seed shatter or secondary dormancy, or that dwarf the recipient could all be useful for mitigation and may have value to the crop. Many such genes have been isolated in the past few years.     

Inexpensive non-toxic flocculation of microalgae contradicts theories; overcoming a major hurdle to bulk algal production

There are two major energy and cost constraints to bulk production of single cell microalgae for biofuels or feed: expensive culture systems with high capital costs and high energy requirements for mixing and gas exchange; and the cost of harvesting using high-speed continuous centrifugation for dewatering. This report deals with the latter; harvesting by flocculation where theory states that alkaline flocculants neutralize the repelling surface charge of algal cells, allowing them to coalesce into a floc. It had been assumed that with such electrostatic flocculation, the more cells to be flocculated, the more flocculant needed, in a linear stoichiometric fashion, rendering flocculation overly expensive. Counter to theory of electrostatic flocculation, we find that the amount of alkaline flocculant needed is a function of the logarithm of cell density, with dense cultures requiring an order of magnitude less base than dilute suspensions, with flocculation occurring at a lower pH. Various other theories abound that flocculation can be due to multi-valent cross-linking, or co-precipitation with phosphate or with magnesium and calcium, but are clearly not relevant with the flocculants we used. Monovalent bases that cannot cross-link or precipitate phosphate work with the same log-linear stoichiometry as the divalent bases, obviating those theories, leaving electrostatic flocculation as the only tenable theory of flocculation with the materials used. The cost of flocculation of dense cultures with this procedure should be below $1.00/T algae for mixed calcium:magnesium hydroxides.     

Direct evidence for the lack of methylation of two pulse labeled plant RNAs

A product of the processing of precursor rRNA ("excess" RNA)has been indirectly found to be unmethylated in mammalian systems,but direct measurement was precluded because of its instability.The "excess" RNA of duckweeds is relatively stable allowingdirect estimation of its methylation by polyacrylamide gel electrophoresis.The "excess" RNA with an apparent molecular weight 0.5?10⁶ wasunmethylated. A pulse labeled RNA with an apparent molecularweight of 1.2?10⁶ (presumably from chloroplasts) was also unmethylated.Under similar conditions the presumed cytoplasmic rRNA precursors,and the mature cytoplasmic and chloroplast rRNAs were methylated. ¹Present address: Department of Biological Sciences, S.U.N.Y.Binghamton, N.Y. 13901, U.S.A. (Received May 9, 1974; )     

Isolation, Identification, and Activity of Mycoherbicidal Pathogens from Juvenile Broomrape Plants

Although there are reports of isolation of mycoherbicidal pathogens attacking the widespread broomrapes (Orobanche spp.) that parasitize legumes and vegetables, none is in use or available. This is despite there being no good method of controlling broomrapes in most crops other than by preplant fumigation with methyl bromide. Two highly parasitic fungi, Fusarium arthrosporioides strain E4a (CNCM I-164) and F. oxysporum strain E1d (CNCM I-1622), were isolated from nearly 100 organisms found on diseased, juvenile, emerging Orobanche flower stalks. A near-axenic polyethylene envelope system for culturing broomrape on tomato roots was used to ascertain pathogenicity of these strains. Both organisms fulfilled Koch's postulates for being primary pathogens. Their DNAs were analyzed and fingerprinted by restriction fragment length polymorphism and random amplified polymorphic DNA, showing that they are indeed different from each other and from many other Fusarium spp. and other formae speciales of F. oxysporum including a strain that attacks O. cumana on sunflowers. Both strains infect O. aegyptiaca, O. cernua, and O. ramosa, but not O. cumana. They did not infect any of the vegetable and legume crops tested and thus seem specific to Orobanche. Tomato plant roots dipped into a fungal spore and mycelial suspension and planted in broomrape-infested soil were protected for 6 weeks, as were tomato transplants in pot experiments. About 90% control was also achieved by posttransplant soil drench with fungal suspensions in pot experiments. These pathogens may be effective as seed, transplant, or soil-drench treatments of high-value vegetable and other crops.