Precursors of ricinine in the castor bean plant

Isotopic tracer experiments confirmed that glycerol and succinic acid are good precursors of the pyridine ring of ricinine in castor bean plants. Tritium from C-2 was lost from tritiated glycerol while tritium from C-1 was retained. Thus a derivative of dihydroxyacetone is likely to be intermediate. By simultaneous feeding of glycerol-1-(3)-[³H] and succinic acid-2(3)-[¹⁴C], it was hoped to find precursors of ricinine containing both labels, but none could be found. There was no evidence for the appearance of labeled quinolinic acid, which is presumed to be a precursor of ricinine.     

Enhanced Sensitivity to Ethylene in Nitrogen- or Phosphate-Starved Roots of Zea mays L. during Aerenchyma Formation

Adventitious roots of maize (Zea mays L. cv TX 5855), grown in a well-oxygenated nutrient solution, were induced to form cortical gas spaces (aerenchyma) by temporarily omitting nitrate and ammonium (-N), or phosphate (-P), from the solution. Previously this response was shown (MC Drew, CJ He, PW Morgan [1989] Plant Physiology 91: 266-271) to be associated with a slower rate of ethylene biosynthesis, contrasting with the induction of aerenchyma by hypoxia during which ethylene production is strongly stimulated. In the present paper, we show that aerenchyma formation induced by nutrient starvation was blocked, under noninjurious conditions, by addition of low concentrations of Ag⁺, an inhibitor of ethylene action, or of aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. When extending roots were exposed to low concentrations of ethylene in air sparged through the nutrient solution, N or P starvation enhanced the sensitivity to exogenous ethylene at concentrations as low as 0.05 microliters ethylene per liter air, promoting a more rapid and extensive formation of aerenchyma than in unstarved roots. We conclude that temporary deprivation of N or P enhances the sensitivity of ethylene-responsive cells of the root cortex, leading to cell lysis and aerenchyma.     

Enhancement of Anaerobic Respiration in Root Tips of Zea mays following Low-Oxygen (Hypoxic) Acclimation

Root tips (10-millimeter length) were excised from hypoxically pretreated (HPT, 4% [v/v] oxygen at 25°C for 16 hours) or nonhypoxically pretreated (NHPT, 40% [v/v] oxygen) maize (Zea mays) plants, and their rates of respiration were compared by respirometry under aerobic and anaerobic conditions with exogenous glucose. The respiratory quotient under aerobic conditions with 50 millimolar glucose was approximately 1.0, which is consistent with glucose or other hexose sugars being utilized as the predominant carbon source in glycolysis. Under strictly anaerobic conditions (anoxia), glycolysis was accelerated appreciably in both HPT and NHPT root tips, but the rate of anaerobic respiration quickly declined in NHPT roots. [U-¹⁴C]Glucose supplied under anaerobic conditions was taken up and respired by HPT root tips up to five times more rapidly than by NHPT roots. When anaerobic ethanol production was measured with excised root tips in 50 millimolar glucose, HPT tissues consistently produced ethanol more rapidly than NHPT tissues. These data suggest that a period of low oxygen partial pressure is necessary to permit adequate acclimation of the root tip of maize to subsequent anoxia, resulting in more rapid rates of fermentation and generation of ATP.     

The effect of turbulent motion on the diffusion of microorganisms

The effect of turbulent fluid motion on the diffusion of simple organisms is discussed. The net reproduction rate and the turbulent flow are assumed to be Gaussian-correlated random variables. For homogeneous istropic turbulence, simple equations for the average concentration of the organisms are derived in terms of the energy density of the fluid. It is shown that the effective diffusivity generated by the motion is positive-definite, and is independent of the helicity of the flow.     

Field evaluation of micropropagated bananas derived from plants containing Banana Bunchy-Top Virus

Micropropagated bananas derived from Banana Bunchy-Top Virus (BBTV) infected plants, but displaying no symptoms of the disease, were established in the field. They were grown for three years and produced a plant crop and ratoon crops. No disease symptoms were observed. There was uncertainty as to whether

The use of immobilized porphyrins and corrins to dehalogenate organochlorine pollutants

Porphyrins and corrins have been immobilized onto solid-phase supports and used to dehalogenate organohalides under reducing conditions. One such system has been used to dehalogenate an aqueous solution (10 ppm) of lindane for over 90 days at over 98% efficiency and for a further 150 days in excess of 65% efficiency. Dichloromethane has been shown to be effectively dehalogenated when supplied to immobilized systems in gaseous form. Correspondence to: T. S. Marks     

Developmental variation in copper,zinc and metallothionein mRNA in brindled mutant and nutritionally copper deficient mice

The concentrations of copper, zinc and metallothionein-I (MT-I) mRNA were determined in the liver, kidney and brain of the brindled mutant mouse from birth until the time of death. Despite accumulation of copper in the kidney of the mutant, MT-I mRNA concentrations were normal. There was no difference between the MT-I mRNA in the brain of mutant and normal in the first 10 days of life, but after day 10 metallothionein mRNA levels were increased in the mutant. The concentration of copper was very low in the liver of the mutant, and on day 6 after birth the metallothionein mRNA was also reduced by about 50%. This reduction was not seen in copper-deficient 6-day-old pups, despite very low hepatic copper levels. This suggests that the lower hepatic MT-I mRNA in the day 6 brindled mouse was not simply due to the reduction in hepatic copper and also that hepatic copper is not regulating metallothionein gene expression the liver of neonatal mice. After day 12 hepatic MT-I mRNA levels were elevated in mutant and in copper deficient mice, both of which die at 14 to 16 days. These increases and the increase in brain MT-I mRNA in older mutant mice are likely to be caused by stress. Overall the results support the conclusions that the brindled mutation does not cause a constitutive activation of the metallothionein genes, and that the differences in metallothionein mRNA between mutant and normal are most probably secondary consequences of the mutation.     

Factors affecting recurrent shoot multiplication in in vitro cultures of 17- to 20-year-old douglas fir trees

Summary The effects of sucrose concentration, addition of ammonium nitrate, and exposure to N⁶-benzyl-adenine (BA) on multiplication potential with shoots derived from shoot cultures of 17- to 20-yr-old Douglas fir trees [Pseudotsuga menziesii (Mirb.) Franco] were compared. Each of these conditions, when compared independently, affected recurrent shoot multiplication and influenced shoot development, as measured by the abundance of shoot apices. Sucrose concentration was influential, the use of 25 g · liter⁻¹ providing twice the multiplication obtained with 20 g · liter⁻¹, and 14 × that obtained with the 30 g · liter⁻¹ concentration routinely used (tree 11). Ammonium nitrate usage also improved multiplication, a 2.5 times improvement being obtained after incorporation of 100 mg · liter⁻¹ NH₄NO₃ into the medium (tree 33). Shoot cultures were responsive but relatively sensitive to addition of BA, the best improvement in multiplication (5 times) being obtained with brief exposures to 3 mg · liter⁻¹ BA (tree 11). Although shoot cultures were responsive to the conditions investigated, differences in shoot multiplication and development were not displayed for several weeks. It was not possible therefore to repeat all the treatments with more than one genotype; however, when this was possible a genotype-dependent variation in response was evident.     

A new model for DNA containing A.T and I.C base pairs.

DNA polymers containing exclusively A.T or I.C base pairs frequently exhibit D- or E-type X-ray diffraction patterns when dried. The distribution of intensities in fiber patterns appears to demand helical structures with 7 and 7.5 bp/turn, respectively, but it is not stereochemically possible to wind a right-handed antiparallel B-family helix this tightly. It is a simple matter, however, to build a left-handed helix with 7-7.5 bp/turn by incorporating Hoogsteen pairing into a Z helix framework. X-ray intensities calculated from this novel left-handed Hoogsteen model provide as reasonable a fit to the D-DNA diffraction pattern as do intensities calculated from previously proposed right-handed 8-fold models.