Tumor-Promoting Phorbol Esters Promote Melanogenesis and Prevent Expression of the Adrenergic Phenotype in Quail Neural Crest Cells

Tumor-promoting phorbol esters were used to manipulate the in vitro development of neural crest cells. When plated at clonal density in secondary culture, quail neural crest cells from the trunk region gave rise to three types of colonies, pigmented, unpigmented, and mixed. Pigmented colonies consisted exclusively of melanocytes; up to 50% of the unpigmented and mixed colonies contained adrenergic nerve cells which could be identified by a catecholamine-specific histofluorescence method. Addition of potent tumor promoters to the culture medium shortened the doubling time of neural crest cells and altered their morphologic appearance. It also delayed the onset of pigmentation, prevented the expression of the adrenergic phenotype, reduced the number of unpigmented and mixed colonies, and increased the number of pigmented colonies, most likely by directing progenitor cells preferentially to the melanogenic pathway. There was a clear correlation between the ability of phorbol esters to promote skin tumors in mice and their ability to interfere with the in vitro development of quail neural crest cells. The potent promoters 12–0–tetradecanoyl phorbol 13–acetate (TPA) and phorbol 12,13–didecanoate (PDD) were most effective, phorbol 12,13–diacetate (PDA) was considerably less effective, the nonpromoting analogues 4–0–methyl 12–0–tetradecanoyl phorbol 13–acetate (4–0–Me-TPA) and 4α-phorbol 12,13–didecanoate (4α-PDD) and the parent alcohol phorbol (PHR) had little or no effect.     

Toxicity of Selenium to the Blue-green Algae, Anacystis nidulans and Anabaena variabilis

Selenate, selenite, selenomethionine, and selenopurine are toxicto Anacystis nidulans and Anabaena variabilis. These compoundsare less toxic in culture medium containing sulphate than insulphur-free medium, thus suggesting a protective role of sulphuragainst selenium toxicity Selenite is more toxic in agar plate cultures and less toxicin liquid cultures than selenate. Cells grown in the highestgrowth-permitting concentration of selenite in liquid mediumform a variable number of red granules No such granulation occursin cells treated with other seleno-compounds, indicating therebythat the mode of selenite action in blue-green algae differsfrom that of other selenium compounds     

A Senescence Factor and Foliar Abscission in Catharanthus roseus

Abscission-accelerating activity was found in naturally senescentpetioles, and senescent leaves of Catharanthus indicating thepresence of a senescence factor (SF) in these tissues. No SFactivity was observed in non-senescent petioles, or non-senescentleaves at various defined developmental stages. The resultsare discussed in relation to the auxin-auxin balance theoryfor the control of leaf abscission and the auxin-SF balancetheory.     

THE EFFECT OF PROFLAVINE ON DIFFERENT STRAINS OF THE BLUE-GREEN ALGA ANACYSTIS NIDULANS

The growth of the blue-green alga Anacystis nidulans was inhibitedby relatively low concentrations of proflavine. The durationof the lag phase increased linearly with increasing proflavineconcentrations. The alga neither acquired increased toleranceto the drug during the course of six subcultures in proflavine-supplementedmedia nor was there any shortening of lag-phase or increasein final population density following repeated subculture inproflavine medium. The strain obtained after six subcultures in proflavine wasfound to have become more sensitive to streptomycin than theuntreated stock strain. A comparison of sensitivity to proflavine of two streptomycin-resistantstrains and of untreated stock strain of the alga revealed thatthe streptomycin-resistant strains were less sensitive to proflavinethan the untreated strain. The resistance of a strain resistant to 200 µg streptomycin/mlwas lost after it had been cultured once in streptomycin-freebasal medium that had been supplemented with 1 µg proflavineµml.The results obtained provide some indirect evidence for theexistence of episome in A. nidulans. ¹Present temporary address: Division of Biosciences, NationalResearch Council, Ottawa-2, Canada.     

Cryopreservation of Shoot Tips of Tetraploid Potato (Solanum tuberosumL.) Clones by Vitrification

In vitro-grown shoot tips of five tetraploid potato (SolanumtuberosumL.) clones were cryopreserved by vitrification. Excisedshoot tips (0.5–0.7 mm) were pre-cultured on filter paperdiscs over half strength liquid Murashige and Skoog (MS) mediumsupplemented with 8.7 µMGA₃and different combinationsof sucrose (0.3, 0.5 and 0.7M) plus mannitol (0, 0.2 and 0.4M)for 2 d under a 16 h photoperiod at 24 °C. The pre-culturedshoot tips were either successively loaded with 20 and 60% PVS2 solutions or directly exposed to concentrated vitrificationsolution before physical vitrification during liquid nitrogentreatment. The vitrified shoot tips were warmed rapidly andtreated with dilution mixture (MS+1.2Msucrose) for 30 min beforeplating on regrowth medium. Addition of mannitol to the pre-culturemedium improved survival of vitrified shoot tips. Direct dehydrationof pre-cultured shoot tips with concentrated PVS 2 was detrimentalto survival of vitrified shoot tips. Shoot tips pre-culturedon medium containing 0.3Msucrose plus 0.2Mmannitol, and loadedwith 20% PVS 2 for 30 min followed by 15 min incubation in 60%PVS 2 and 5 min incubation in 100% PVS 2 at 0 °C resultedin up to 54% survival after vitrification. About 50% of vitrifiedand warmed shoot tips formed shoots directly. Post-thaw culturingof vitrified shoot tips on medium containing an elevated levelof sucrose (0.2M) under diffuse light for the first week enhancedthe survival rate. Continuous culturing of vitrified shoot tipson high-sucrose medium induced multiple shoot formation.Copyright1998 Annals of Botany Company Solanum tuberosumL., potato, cryopreservation, germplasm conservation,in vitroconservation, meristems, shoot tips, tissue culture, vitrification.     

Comparative activity of three repellents against the ticks Rhipicephalus sanguineus and Argas persicus

The residual repellent activity of N,N-diethylphenyl-acetamide (DEPA), N,N-diethyl-3-methyl benzamide (DEET) and dimethylphthalate (DMP) against the hard tick Rhipicephalus sanguineus (Latreille) and the soft tick Argas persicus (Oken) from topical application on rabbits and hens respectively in the laboratory have been studied. It was found that a 25% concentration of DEET gave strong repellency (greater than 90%) against larvae and nymphs of R. sanguineus for 15 and 7 days respectively and against A. persicus larvae and nymphs greater than 90% for 11 and 5 days respectively. Strong repellency (greater than 90%) against adults of the hard and soft ticks was observed for 9 and 7 days respectively with 40% DEET. DEPA at 25% concentration showed strong repellency (greater than 90%) against larvae and nymphs of R. sanguineus and A. persicus for 11 and 5 days respectively. Adults of hard and soft ticks were strongly repelled (greater than 90%) for 9 and 5 days respectively by 40% DEPA. DMP was found to be the least effective against all stages of both species of tick.