Nonlegume hemoglobin genes retain organ-specific expression in heterologous transgenic plants.

Hemoglobin genes from the nitrogen-fixing nonlegume Parasponia andersonii and the related non-nitrogen-fixing nonlegume Trema tomentosa have been isolated [Landsmann et al. (1986). Nature 324, 166-168; Bogusz et al. (1988). Nature 331, 178-180]. The promoters of these genes have been linked to a beta-glucuronidase reporter gene and introduced into both the nonlegume Nicotiana tabacum and the legume Lotus corniculatus. Both promoters directed root-specific expression in transgenic tobacco. When transgenic Lotus plants were nodulated by Rhizobium loti, both promoter constructs showed a high level of nodule-specific expression confined to the central bacteroid-containing portion of the nodule corresponding to the expression seen for the endogenous Lotus leghemoglobin gene. The T. tomentosa promoter was also expressed at a low level in the vascular tissue of the Lotus roots. The hemoglobin promoters from both nonlegumes, including the non-nodulating species, must contain conserved cis-acting DNA signals that are responsible for nodule-specific expression in legumes. We have identified sequence motifs postulated previously as the nodule-specific regulatory elements of the soybean leghemoglobin genes [Stougaard et al. (1987). EMBO J. 6, 3565-3569].     

Identification of fungi for sweet whey permeate utilization and eicosapentaenoic acid production

Summary Eighteen selected organisms of theEumycota division of the fungi kingdom were examined for eicosapentaenoic acid production and utilization of sweet whey permeate. The organisms belong to the subdivisionsMastigomycotina, Zygomycotina, Ascomycotina andDeuteromycotina. Seven organisms were initially identified as lactose utilizers (the predominant sugar in sweet whey permeate_ and eicosapentaenoic acid (EPA) producers. Utilization of lactose was demonstrated and EPA production was confirmed for four organisms, all of the subdivisionMastigomycotina. Growth studies showed thatP. ultimum had the best potential for future work.     

Effect of abscisic acid, osmolarity and partial desiccation on the development of recalcitrant mango somatic embryos

Inhibition of mango somatic embryo growth was inducedin vitro by treatments for 4 or more weeks with abscisic acid (0–100 M ABA) with and without high osmolarity provided by mannitol (0–10%). High osmolarity and ABA significantly affected somatic embryo length, precocious germination and the production of good quality secondary somatic embryos. High osmolarity also affected root elongation. Abscisic acid was more effective in suppressing growth and development of 0.5 cm-length somatic embryos than smaller somatic embryos. Development beyond the heart stage was significantly inhibited by both ABA and mannitol treatments. The recovery of good quality somatic embryos was enhanced by high levels of ABA (100 M) with and without mannitol (0–5%). Somatic embryos that had been pulsed with ABA were partially desiccated at different relative humidities. Weight loss was affected only by relative humidity; and ABA did not enhance desiccation tolerance.Abbreviations ABA Abscisic acid - 2,4-D 2,4-Dichlorophenoxyacetic acid - MM1 Mango maturation medium - RH Relative humidity     

Characteristics of microwave evoked body movements in mice

Microwave evoked body movements were studied in mice. A resonant cavity was used to provide head and neck exposure of the mouse to pulsed and gated continuous wave (CW) 1.25 GHz microwaves. No difference in response to pulsed and gated CW stimuli of equal average power was found. The incidence of the microwave evoked body movements increased proportionally with specific absorption (dose) when the whole-body average specific absorption rate was at a constant level (7300 W/kg). Under a constant average specific absorption rate, the response incidence reached a plateau at 0.9 kJ/kg. For doses higher than 0.9 kJ/kg, response incidence was proportional to the specific absorption rate and reached a plateau at 900 W/kg. Body movements could be evoked by a single microwave pulse. The lowest whole-body specific absorption (SA) tested was 0.18 kJ/kg, and the corresponding brain SA was 0.29 kJ/kg. Bulk heating potentials of these SAs were less than 0.1 °C. For doses higher than 0.9 kJ/kg, the response incidence was also proportional to subcutaneous temperature increment and subcutaneous heating rate. The extrapolated absolute thresholds (0% incidence) were 1.21 °C temperature increment and 0.24 °C/s heating rate. Due to high subcutaneous heating rates, these microwaves must be perceived by the mouse as an intense thermal sensation but not a pain sensation because the temperature increment was well below the threshold for thermal pain. Results of the present study should be considered in promulgation of personnel protection guideline against high peak power but low average power microwaves. © 1994 Wiley-Liss, Inc.     

Fluorescence lifetime analysis of DNA intercalated ethidium bromide and quenching by free dye

The fluorescence characteristics of ethidium bromide (Eb) complexed to calf thymus DNA have been examined using fluorescence lifetime analysis for a range of DNA (effective nucleotide concentration) to Eb molar ratios. Control of both temperature and ion concentration is necessary for reproducible analyses. Eb complexed to double stranded DNA has a maximum fluorescence lifetime of 23 ns and is easily distinguishable from a fluorescence lifetime value of 1.67 ns corresponding to unbound Eb. In a solution of calf thymus DNA containing excess Eb a binding equilibrium is reached, and this corresponds to one Eb molecule for every five nucleotides. With increasing amounts of unbound Eb, the fluorescence lifetime of the DNA-Eb complex decreases with a concomitant drop in the steady state fluorescence intensity, without a change in the amount of Eb bound to DNA. It is concluded that unbound Eb, acting via a quenching mechanism, shortens the fluorescence lifetime of bound Eb and consequently decreases the overall fluorescence intensity. This means that a different approach is necessary: time-resolved fluorescence spectroscopy directly distinguishes between a decrease in fluorescence intensity due to quenching by an excess of unbound Eb from that due to a decrease in Eb binding to double-stranded DNA. These studies suggest that techniques which measure total steady state fluorescence intensity of bound Eb in order to infer relative amounts of double-stranded DNA must be interpreted with caution. For such assays to be valid it is essential that no unbound Eb be present; otherwise a variable correction factor is required to account for unbound Eb.