We should be concerned.
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Alcohol Drinking↗
Biomedical subjects
M L Christianson
Publications and source records attributed to M L Christianson.
Phenocritical times in the process of in vitro shoot organogenesis.
Shoot organogenesis occurs when leaf explants of Convolvulus arvensis are cultured on Murashige and Skoog salts, sucrose, vitamins, and 0.05 mg/liter IAA with 7.0 mg/liter 2-isopentenyl adenine. Under the influence of this shoot inducing medium (SIM), the explants become competent for the organogenic effects of SIM and eventually become determined for shoot formation. The induction process includes five separate transient sensitivities to inhibitors. Such stage-specific inhibitions reflect phenocritical times in development rather than general metabolic toxicities. The phenocopying agents are tri-iodobenzoic acid (TIBA), sorbitol, ribose, ammonium ion, and acetylsalicylic acid. The process of in vitro shoot organogenesis from leaf explants is now seen to include a series of discrete steps which precede morphological differentiation. An initial dedifferentiation process results in the formation of competent callus tissue along the cut edges of the explant. Under the influence of the phytohormone balance in SIM, shoot organogenic induction proceeds. This process involves a time which is sensitive to inhibition by salicylates followed by a time sensitive to TIBA which is followed in turn by a time sensitive to sorbitol and culminates in cells or groups of cells determined for shoot formation. This process also includes a time sensitive to inhibition by ribose, although its place in the order of events is not yet firmly assigned. There is also a sensitivity to ammonium ion (or lack of nitrate) at or near the time the explant becomes determined for shoot production.
Aspirin↗
Dental Profession Advisory Program alive and well in British Columbia.
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Adaptation, Psychological↗
Use of haploid plants as bioassay for mutagens.
Results of a pilot program show that suspension cultured polyhaploid Nicotiana tabacum cells can be used to bioassay the effects of mutagens. Reproducible survival curves with significant regression coefficients are obtained. Putative mutation conferring resistance to amino acid analogs is significantly more frequent after exposure to mutagens; in contrast, habituants, cytokinin-independent clones, are significantly less frequent (although the variance of clone size increases!). The maximum spontaneous mutation rate is estimated at 3 X 10(-8); the equilibrium frequency of habituant cells in an otherwise nonhabituated culture is estimated at 5 X 10(-7). An evaluation of the system suggests changes in several and further characterization of other of the parameters involved. The use of haploid tobacco as an in vivo mutagen screen is briefly described, as is the importance of similar in vivo diploid systems for discriminating between various kinds of mutational processes.
Amino Acids↗