Promotion of petunia (Petunia hybrida L.) regeneration in vitro by ethylene

The influence of ethylene on shoot and root formation from petunia leaf explants was studied in cultures in test tubes placed in 51 glass jars. Reduction of the endogenously produced ethylene by inclusion of ethysorb (KMnO₄), an ethylene absorbent, caused a decrease of the number of shoots. On the other hand, supplementing the cultures with ethylene (0.01–10 ppm) caused a marked increase of the number of shoots without, however, any effect on the length and fresh weight. Ethylene treatments (1 ppm) were found to be most effective when they were applied in the second week of culturing of petunia explants. Addition of Co⁺⁺ to the medium resulted in a reduction of the endogenously produced ethylene and concomitantly reduced shoot formation. Similarly, inclusion of Ag⁺, an inhibitor of ethylene action, resulted in poor shoot formation. Ethylene also appeared to play a role on rooting of petunia microshoots in vitro in an auxin-free medium. Ethylene at a concentration of 10 ppm induced adventitious root formation considerably, whereas at low levels (0.01–1 ppm) it had no influence on rooting.     

Is dispersal of fish eggs,embryos and larvae an insurance against density dependence?

Synopsis Dispersal of eggs, embryos and larvae appears to be an effective mechanism for maintaining the densities of fish larvae at sea below levels at which competition for food becomes a critical survival factor. A hypothesis that competition is the selective agent for the evolution of dispersal, also involving unfavourable transportation as a trade-off of dispersal, is proposed. The validity of this hypothesis is investigated by seeking for adaptive connections between the dispersal or retention tendencies and the ecological or biological properties of the species.     

Reproductive strategies and early development of three freshwater gobies

Three species of gobiid fish inhabit the freshwater Lake Trichonis of western Greece. Two of these species, Economidichthys pygmaeus and E. trichonis are endemic, and the third is the widespread Knipowitschia caucasica . There are habitat separations between the three species, E. pygmaeus and E. trichonis prefer vegetated areas, the first being fully demersal at all stages of development and the second being semi-demersal. Knipowitschia caucasica prefers sandy bottoms and is distributed in shallower waters. Female E. pygmaeus and E. trichonis spawn in nests prepared by the males in the cavities of broken reeds. The males subsequently guard the eggs until they hatch, with females playing no role in parental care. Economidichthys trichonis is probably the smallest freshwater European species. Its eggs are ovoid, measuring about 0.64 × 0.58 mm, from which tiny, unpigmented and incompletely developed pelagic larvae hatch out after an incubation period lasting less than 1 day at a water temperature of 19.5° C. The eggs of E. pygmaeus are cylindrical and larger, measuring about 2.38 × 0.89 mm, from which relatively large, strongly pigmented and ontogenetically more advanced larvae hatch out after a longer incubation period. Both species reproduce only once in their lifetime, at the age of 1 year, and die shortly after spawning, but the breeding season involves several spawnings by each individual fish. These biological, developmental and reproductive characteristics are discussed in relation to current theories on evolution of life-historics.     

Sodium molybdate increases the amount of progesterone and estrogen receptor detected in certain human breast cancer cytosols

When sodium molybdate is added at a final concentration of 20 mM, additional 85 and 4S progesterone (³ H-R5020) receptor can be detected in the cytosols from a number of human breast cancers. Additional estrogen receptor also could be measured in some cytosols, and a quantitative temperaturedependent conversion of 8S to 4S binding molecules achieved. Sodium molybdate also prevented the loss of binding activity that occurred when cytosols were incubated at 30° in the absence of added estradiol. In addition to increasing the amount of progesterone receptor, and to a lesser extent estrogen receptor that may be detected, elucidation of the mechanism by which this salt stabilized receptors should contribute to further understanding of how cytosol steroid receptor content and function is regulated.     

Direct radioimmunoassay for diethylstilbestrol in serum

A radioimmunoassay method for the measurement of diethylstilbestrol directly on 50 microliters of human serum was established using a tritium-labeled radioligand and a double antibody as a separation reagent. The assay was sensitive (less than 0.17 micrograms/L), reproducible (intra-assay and interassay coefficient of variation values, 8.14% and 8.25%, respectively), and accurate (recovery up to 95%). Factors influencing the assay are identified and discussed.