The biology and physiology of alga-invertebrate symbioses. III. In situ measurements of photosynthesis and calcification in some hermatypic corals

In situ measurements of the rates of photosynthesis and calcification in three species of hermatypic corals were made at Eilat, in the Gulf of Aqaba, Red Sea. Experiments were made at 5, 20 and 35 m depth under unusually poor conditions of submarine illumination for the region, and at the relatively low water temperature (21°C) for coral growth which prevails there all year. Estimates of photosynthetic rates by both the ¹⁴C and oxygen methods indicated that the ¹⁴C method does measure gross photosynthesis in these organisms even at, and below, light compensation points. Substantial rates of carbon fixation in Acropora and Millepora show that, even under bad conditions, these organisms could survive autotrophically to at least 10 m depth, as also could the massive coral Goniastrea although this had much lower photosynthetic rates under the same conditions, compensated for by a much lower respiratory rate than the other two corals.Calcification rates were variable but showed a considerable increase in light as compared with the dark in all three species, and the rates did not decrease with depth as much as might have been anticipated from the reduction in photosynthesis and ambient light energy. Photosynthetic and calcification rates were similar to those reported for similar organisms both in the Caribbean and on the Great Barrier Reef.     

An experiment in enzyme evolution studies withPseudomonas aeruginosa amidase

The regulation of amidase synthesis inP. aeruginosa is under positive control. This review describes the experimental evolution of amidase and its regulator protein for the hydrolysis of novel substrates and experiments to elucidate the mechanism of the control system.     

Metabolic Acclimation to Anoxia Induced by Low (2-4 kPa Partial Pressure) Oxygen Pretreatment (Hypoxia) in Root Tips of Zea mays

Young intact plants of maize (Zea mays L. cv INRA 508) were exposed to 2 to 4 kilopascals partial pressure oxygen (hypoxic pretreatment) for 18 hours before excision of the 5 millimeter root apex and treatment with strictly anaerobic conditions (anoxia). Hypoxic acclimation gave rise to larger amounts of ATP, to larger ATP/ADP and adenylate energy charge ratios, and to higher rates of ethanol production when excised root tips were subsequently made anaerobic, compared with root tips transferred directly from aerobic to anaerobic media. Improved energy metabolism following hypoxic pretreatment was associated with increased activity of alcohol dehydrogenase (ADH), and induction of ADH-2 isozymes. Roots of Adh1⁻ mutant plants lacked constitutive ADH and only slowly produced ethanol when made anaerobic. Those that were hypoxically pretreated acclimated to anoxia with induction of ADH2 and a higher energy metabolism, and a rate of ethanol production comparable to that of nonmutants. All these responses were insensitive to the presence or absence of NO₃⁻. Additionally, the rate of ethanol production was about 50 times greater than the rate of reduction of NO₃⁻ to NO₂⁻. These results indicate that nitrate reductase does not compete effectively with ADH for NADH, or contribute to energy metabolism during anaerobic respiration in this tissue through nitrate reduction. Unacclimated root tips of wild type and Adhl⁻ mutants appeared not to survive more than 8 to 9 hours in strict anoxia; when hypoxically pretreated they tolerated periods under anoxia in excess of 22 hours.     

Modulation of rat granulocyte traffic by a surface active agent in vitro and bleomycin injury

Pluronic F68 (F68) is a nonionic surfactant which has been reported to inhibit the in vitro adherence and migration of polymorphonuclear leukocytes (PMN) obtained from some species. We demonstrated similar effects on PMN obtained from rats, with diminished adherence to nylon wool and diminished chemotaxis toward zymosan-activated serum. We then examined the in vivo effects of 12-hr F68 infusion on the injury induced by intratracheal bleomycin instillation (ITB) in rats. When sacrificed 24 hr following injury, rats demonstrated neutrophilia, neutrophil-prominent lung lavage cellularity, and increased lung weights. F68 decreased lavage leukocyte counts and lung weight gain in ITB-injured animals. Lung weights of ITB-injured animals correlated (r = 0.81, P less than 0.001) with logarithmic values of lavage PMN. F68 also enhanced neutrophilia and decreased spleen weight gain in injured animals. The acute effects of F68 on circulating leukocyte counts, osmolality, and total complement were also examined. The data demonstrate that F68 can affect PMN traffic both in vitro and in vivo. The data also confirm the prominence of PMN in lavage fluid early in ITB injury, and suggest that an influx of relatively few PMN is associated with lung weight gain in this model.     

In vitro culture of adult and juvenile bud explants of Passiflora species

Cultivar E23, an F1 hybrid of P. edulis and P. edulis f. flavicarpa is usually propagated by shoot-tip grafting. Various media were tested to evaluate the potential of E23 for in vitro propagation. Adult tissue was difficult to culture and did not respond to media containing low (<10 µM) concentrations of growth regulators. Growth of adult buds on intact stem sections was promoted by 1 week of dark incubation on MS basal medium plus 150 µM 2iP, 200 µM adenine sulphate and 17.1 µM IAA (3 mg l^–1), and further developed into shoots on MS medium plus 4.9 µM 2iP (1 mg l^–1) and 5.7 µM IAA (1 mg l^–1). By contrast, juvenile shoots of E23, and Passiflora species: edulis f. flavicarpa, edulis, alata, caerulea, mollissima, coccinea, herbertiana and suberosa grew rapidly on MS medium plus 10 µM kinetin and 5 µM IAA. Rapid multiplication was achieved on MS plus 20 µM BA, 10 µM kinetin, 5 µM IAA, and roots initiated on MS plus 5 µM IAA.Abbreviations IAA indole-3-acetic acid - 2iP N6-iso pentenyl adenine - BA N6-benzyl adenine     

Larger adenylate energy charge and ATP/ADP ratios in aerenchymatous roots of Zea mays in anaerobic media as a consequence of improved internal oxygen transport

Internal transport of O₂ from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O₂ transport) in non-aerenchymatous roots.Abbreviation AEC adenylate energy charge     

Echinomycin and distamycin induce rotation of nucleosome core DNA.

When nucleosome cores reconstituted from chicken erythrocyte histones and a 160 bp DNA molecule are exposed to echinomycin, a bis-intercalating antitumour antibiotic, the DNA appears to rotate with respect to the histone octamer by about half a turn. New bands appear in patterns of DNAase I digestion at positions approximately mid-way between those characteristic of control core samples, while the control pattern is largely suppressed. Similar (but not identical) changes are produced when nucleosome cores are exposed to distamycin, a non-intercalating DNA-binding antibiotic. The effects of both ligands can be explained in terms of a change in rotational orientation of the core DNA, so as to place antibiotic binding sites on the inward-facing (concave) surface of the DNA supercoil. Presumably this serves to optimise non-bonded contacts with the polynucleotide backbone. These results establish that the positioning of DNA about the histone octamer is not absolutely determined by its nucleotide sequence, but may be modified by the binding of such relatively small molecules as antibiotics.