FLUENCE RATE COMPENSATION OF THE PERCEPTION OF RED: FAR-RED RATIO BY PHYTOCHROME IN LIGHT-GROWN SEEDLINGS*

Abstract— The hypothesis that phytochrome functions as a sensor of vegetational shade through the perception of the red: far-red photon fluence rate ratio requires that the mechanism of perception be compensated for wavelength-independent fluctuations in fluence rate (Smith, 1982). This paper seeks to establish the lower limit of fluence-rate compensation and to assess whether or not compensation is effective at the total fluence rates typical of herbaceous canopies. Using specially-designed cabinets, Sinapis alba L. (white mustard) seedlings were grown from germination under a range of total photosynthetically-active radiation (PAR = 400 to 700 nm) values and a range of red: far-red ratios. The data indicate that fluence-rate compensation is effective above a PAR value of ca. 60 μ.mol m² s'. Pretreating seedlings at high red: far-red ratio and a PAR level of 300 (μmol m₂S_-1for increasing periods of time led to an extension of fluence rate compensation to lower fluence rates. The results are discussed in relation to the photosynthetic competence of the seedlings grown under these conditions.     

Side-hole to anti-hole conversion in time-resolved transient spectral hole-burning of emerald: ground state level versus excited state population storage in low magnetic fields

Time-resolved transient spectral hole-burning experiments in zero field and in low magnetic fields B( parallelc) are reported for the chromium(III) R(1)-line, 2A((2)E)<-- 2A((4)A(2)) of Chatham lab created emerald, Be(3)Al(2)Si(6)O(18)ratio Cr(III)(0.0017% per weight), in the temperature range of 3 to 12 K. In low magnetic fields and temperatures >5 K conversion of side-holes to anti-holes is observed with progressing time. Anti-holes are due to the population stored in ground state levels. The dynamics of the hole pattern can be well modelled by a set of coupled differential equations for the levels of the (4)A(2) and (2)E multiplets. The measurements allow the simultaneous determination of g-factors and spin-lattice relaxation rates in the excited state and the ground state. At 6 K the relaxation times between the split +/-1/2 2A((2)E) excited state levels and +/-3/2 2A((4)A(2)) levels of the ground state are about 0.16 ms and 9 ms, respectively. From the temperature dependence it follows that the spin-lattice relaxation rates are dominated by Orbach processes in the experimental temperature range.     

14 MeV neutron activation analysis applied to a non-aqueous flowing system

The feasibility and advantages of fast neutron activation analysis in a non-aqueous flowing system, using economical irradiation techniques are outlined. The application of the method to the determination in solution of elements producing isotopes with half lives in the range 588—29.4 sec, the selection of the optimum flow rate to minimise interferences for each element, and their limits of detection are also given. A method for the prediction of the optimum flow rate, on a given system, for the determination of any element producing an isotope of known half life is also given.     

Monitoring of a heterogeneous reaction by acoustic emission

The feasibility of monitoring the reaction of itaconic acid and 1-butanol by non-invasive acoustic emission measurements has been assessed. A piezoelectric transducer with a resonant mode at 90 kHz was attached to the external wall of a 1 L jacketed glass reactor. Acoustic emission from the oil jacket, stirrer and toluene was insignificant in comparison to that produced by the itaconic acid particles, which was transmitted through the glass walls and heating oil to the transducer. The transducer responded to acoustic emission from itaconic acid up to approximately 300 kHz, with the region around 90 kHz having the highest sensitivity. The effect of particle concentration and size on the acoustic emission generated has also been investigated, with higher concentrations and larger particles giving the greater signals. The detection limit for itaconic acid particles was 14 g dm(-3) of toluene. The effect of 1-butanol concentration and temperature on the progression of reactions was monitored using acoustic emission. It was possible to detect differences in the rate and extent of the reaction under different conditions, and also to identify when a combination of the concentration and/or size of itaconic acid particles had reached a steady state. However, it was not possible to differentiate between changes in particle size and concentration using the resonant transducer.     

Improved micro-flame detection method for gas chromatography

A previously developed micro-counter-current flame method is modified to provide both sensitive photometric and ionization detection for gas chromatography (GC). A stainless steel capillary (0.254 mm i.d.) supplying oxygen functions as a burner, which supports a compact flame that burns in a counter-flowing excess of hydrogen. In the “micro-flame photometric detector” (μFPD) response mode, the background emission level is reduced by over an order of magnitude compared to previous experiments using a fused silica capillary burner, resulting in greatly improved detection limits. Chemiluminescent sulfur response in the μFPD is quadratic over 3.5 orders of magnitude, yielding a detection limit of 3 × 10⁻¹¹ gS/s, while that of phosphorus is linear over 5 orders of magnitude down to a minimum detectable limit of 3 × 10⁻¹² gP/s. Tin response is examined for the first time in the μFPD and yields a blue luminescence (ascribed to SnO*) on the surface of the quartz flame enclosure. Although this emission provides a sensitive detection limit near 6 × 10⁻¹⁵ gSn/s, due to the limited surface area within the detector cell it only produces a linear response range of one order of magnitude. Ionization response toward hydrocarbons is also obtained from the hydrogen-rich micro-counter-current flame. A linear response is produced over five orders of magnitude, yielding a detection limit toward carbon of 2 × 10⁻¹⁰ gC/s. Analysis of a simple gasoline sample is used to demonstrate that the device can successfully operate as both a selective and universal GC detector. Results indicate that this micro-counter-current flame method yields comparable performance to conventional flame photometric and flame ionization detectors, making it potentially useful for adaptation to micro-analytical devices and portable GC units.     

Spontaneous generation of amphiphilic block copolymer micelles with multiple morphologies through interfacial Instabilities

We introduce a method for the formation of block copolymer micelles through interfacial instabilities of emulsion droplets. Amphiphilic polystyrene-block-poly(ethylene oxide) (PS-PEO) copolymers are first dissolved in chloroform; this solution is then emulsified in water and chloroform is extracted by evaporation. As the droplets shrink, the organic solvent/water interface becomes unstable, spontaneously generating a new interface and leading to dispersion of the copolymer as micellar aggregates in the aqueous phase. Depending on the composition of the copolymer, spherical or cylindrical micelles are formed, and the method is shown to be general to polymers with several different hydrophobic blocks: poly(1,4-butadiene), poly(-caprolactone), and poly(methyl methacrylate). Using this method, hydrophobic species dissolved or suspended in the organic phase along with the amphiphilic copolymer can be incorporated into the resulting micelles. For example, addition of PS homopolymer, or a PS-PEO copolymer of different composition and molecular weight, allows the diameter and morphology of wormlike micelles to be tuned, while addition of hydrophobically coated iron oxide nanoparticles enables the preparation of magnetically loaded spherical and wormlike micelles.