Production and Biological Activity of Secalonic Acid D

Twenty isolates of Penicillium oxalicum produced secalonic acid as their major secondary metabolite. Fermentation conditions were determined for toxin production in grain and liquid media. The 50% lethal dose value for mice ranged from 26.5 to 51.7 mg/kg dependent on animal strain and sex, males being more susceptible than females. Secalonic acid was nontoxic and nonteratogenic to the chicken embryo and exhibited poor antibiotic properties. Its potential role in mycotoxicoses is discussed.     

Amber mutations in Escherichia coli essential genes: isolation of mutants affected in the ribosomes.

Summary A method to obtain amber mutations in ribosomal protein genes is described. It relies on the P1-mediated localized mutagenesis (Hong and Ames, 1971) and on the fact that the recipient strain contains (a) an efficient but genetically unstable suppressor, (b) a particular thermoinducible prophage which kills suppressor hosts at 42° C. Exposure of these bacteria to the high temperature yields frequent suppressor-free derivatives while none will be found if the strain carries an amber mutation in an essential gene. Eleven mutants have been isolated by this method, of which at least six appear to carry amber mutations. All of them map close to, and to the right of spcA, in a region which codes mostly for ribosomal proteins. Three mutants were studied biochemically; all three show defective ribosomal assembly in vivo upon loss of suppression.     

Polyamines in Paul's Scarlet rose suspension cultures

Polyamine concentrations have been determined at intervals in suspension cultures of Paul's Scarlet rose cells during a culture period of 2 weeks. The mean concentrations of the putrescine, spermidine and spermine in the cells of the inocula were respectively 73, 70 and 13 nmol/g fresh weight. Putrescine at fitst increased with a peak (160 nmol/g) after 6 h, declined to a minimum (14 nmol/g) after 2–3 days, increased to a second peak (180 nmol/g) after 5–6 days, and then declined slowly to the concentration of the inoculum (taken on day 14). Spermidine rose slowly (×2.6) to a broad peak over 3–6 days (180 nmol/g), then declined slowly to the concentration in the inoculum. Spermine showed a rapid increase to a peak (130 nmol/g) after 2–3 days, and then declined rapidly, reaching the inoculum concentration by day 6. In one experiment the three amines showed a minor peak at day 11. Changes in spermine and RNA contents appeared to be correlated. DNA content reached a peak after that of the RNA (day 3) and did not appear to be correlated with the content of putrescine or the polyamines.     

Cytochemical and electron microscopic demonstration of organelle translocation and the inhibition of such translocation by colchicine during the mitosis of rat hepatocytes

Hepatocyte lysosomes, mitochondria, and peroxisomes show a dramatic translocation during mitosis induced by partial hepatectomy. During prophase, all three organelles move to the perinuclear cytoplasm. In metaphase, they become concentrated in the polar regions. During telophase, these organelles form clusters in the juxtanuclear regions. This organelle translocation is inhibited by the administration of a low concentration of colchicine, suggesting an involvement of microtubules in their movement.     

The isometric length-force models of nine different skeletal muscles.

The length-force relations of nine different skeletal muscles in the hindlimb of the cat were determined experimentally, with electrical stimulation of the sciatic nerve as the activation mode. It was shown that the active-, passive-, and total-force patterns varied widely among the muscles. The tibialis posterior (TP), medial and lateral gastrocnemius (MG, LG) and flexor digitorum longus (FDL) had a symmetric active-force curve, whereas the tibialis anterior (TA), peroneus brevis (PB), peroneus longus (PL), extensor digitorum longus (EDL), and soleus (SOL) had an asymmetric curve which exhibits about 25% of the maximal isometric force at extreme lengths. The SOL, EDL, and LG had a low-level passive force which appeared at short muscle length, whereas all other muscles exhibited initial passive force just before the optimal length. The total force was rising quasi-linearly for the SOL, whereas the other muscles exhibited an intermediate plateau about the optimal length. The LG and FDL had a substantial but temporary intermediate dip in the total force as the muscle was elongated past the optimal length. The elongation range of the various muscles also varied, ranging from +/- 15 to +/- 30% of the optimal length. The elongation range was symmetric for the FDL, LG, MG, TP, SOL, and EDL, and asymmetric for the PL, PB, and TA, being -12 to + 17%, -12 to + 17%, and -35 to + 12%, respectively. Two different models which incorporate muscle architecture were successfully fitted to the experimental data of the muscles except for the MG and TA. The architecture of these two muscles is highly nonhomogeneous and contains compartments with two pennation patterns or two different optimal lengths. New models, which add spatially and temporally the individual characteristics of each compartment of the muscles, were constructed for these two muscles. The new models demonstrated high correlation to the experimental data obtained from the MG and TA. It was concluded that the length-force relation varies widely among various skeletal muscles and is probably dependent on the primary function of the muscle in the context of integrated movement; this is a manifestation of architectural factors such as fiber pennation pattern and angle, cross-sectional area, ratio of muscle to tendon length, distribution of the fiber length within the muscle and compartmental pennation.     

Light-grown plants of transgenic tobacco expressing an introduced oat phytochrome A gene under the control of a constitutive viral promoter exhibit persistent growth inhibition by far-red light

A comparison of the photoregulation of development has been made for etiolated and light-grown plants of wild-type (WT) tobacco (Nicotiana tabacun L.) and an isogenic transgenic line which expresses an introduced oat phytochrome gene (phyA) under the control of a constitutive viral promoter. Etiolated seedlings of both the WT and transgenic line showed irradiance-dependent inhibition of hypocotyl growth under continuous far-red (FR) light; transgenic seedlings showed a greater level of inhibition under a given fluence rate and this is considered to be the result of the heterologous phytochrome protein (PhyA) functioning in a compatible manner with the native etiolated phytochrome. Deetiolation of WT seedlings resulted in a loss of responsiveness to prolonged FR. Light-grown transgenic seedlings, however, continued to respond in an irradiance-dependent manner to prolonged FR and it is proposed that this is a specific function of the constitutive PhyA. Mature green plants of the WT and transgenic lines showed a qualitatively similar growth promotion to a brief end-of-day FR-treatment but this response was abolished in the transgenic plants under prolonged irradiation by this same FR source. Growth inhibition (McCormac et al. 1991, Planta 185, 162–170) and enhanced levels of nitrate-reductase activity under irradiance of low red:far-red ratio, as achieved by the FR-supplementation of white light, emphasised that the introduced PhyA was eliciting an aberrant mode of photoresponse compared with the normal phytochrome population of light-grown plants. Total levels of the oat-encoded phytochrome in the etiolated transgenic tobacco were shown to be influenced by the wavelength of continuous irradiation in a manner which was qualitatively similar to that seen for the native, etiolated tobacco phytochrome, and distinct from that seen in etiolated oat tissues. These results are discussed in terms of the proposal that the constitutive oat-PhyA pool in the transgenic plants leads to a persistence of a mode of response normally restricted to the situation in etiolated plants.Abbreviations FR far-red light - R red light - WL white light - WL + FR white light supplemented with FR - HIR high-irradiance response - PAR photosynthetically active radiation - Pr, Pfr R- and FR-absorbing forms of phytochrome - Ptot total phytochrome - phyA (PhyA) gene (encoded protein) for phytochrome - WT wild type This work was supported by an Agricultural and Food Research Council research grant to H.S. and A.M.; J.R. Cherry and R.D. Vierstra, (Department of Horticulture, University of Wisconsin-Madison, USA) are thanked for the provision of the transgenic tobacco line.     

An assessment of the importance of emergent and floating-leaved macrophytes to trophic status in the Loosdrecht lakes (The Netherlands)

The potential importance of the six major emergent and floating-leaved macrophyte species in recycling of sediment phosphorus in the Loosdrecht lakes was studied. Representative plant samples were collected at the time of maximum biomass, and analysed for biomass and carbon, nitrogen and phosphorus contents. Species cover was determined by aerial photography.Total cover in the seven lakes studied ranged between 2 and 26 percent. For the four main species, biomass per unit area increased with lake trophic status. Consistent differences in C, N and P contents per unit biomass were not observed. Although cover values were small, significant amounts of C, N and P were contained in the macrophytes when compared with maximum sestonic content.Potential P loads from macrophyte decay were calculated. In Lake Loosdrecht, the P load represented 15 percent of current external P inputs. The potential importance of macrophyte decay to P recycling in the other lakes is greater.Decay of macrophyte species at the end of the growing season appears to affect autumnal nutrient and chlorophyll a levels in the water column of some lakes. The re-establishment of submerged species following lake restoration may increase the importance of this pathway in the lakes.