RESUMO
Selection of kochia (Kochia scoparia) biotypes resistant to the sulfonylurea herbicide chlorsulfuron has occurred through the continued use of this herbicide in monoculture cereal-growing areas in the United States. The apparent sulfonylurea resistance observed in kochia was confirmed in greenhouse tests. Fresh and dry weight accumulation in the resistant kochia was 2- to >350-fold higher in the presence of four sulfonylurea herbicides as compared to the susceptible biotype. Acetolactate synthase (ALS) activity isolated from sulfonylurea-resistant kochia was less sensitive to inhibition by three classes of ALS-inhibiting herbicides, sulfonylureas, imidazolinones, and sulfonanilides. The decrease in ALS sensitivity to inhibition (as measured by the ratio of resistant I(50) to susceptible I(50)) was 5- to 28-fold, 2- to 6-fold, and 20-fold for sulfonylurea herbicides, imidazolinone herbicides, and a sulfonanilide herbicide, respectively. No differences were observed in the ALS-specific activities or the rates of [(14)C]chlorsulfuron uptake, translocation, and metabolism between susceptible and resistant kochia biotypes. The K(m) values for pyruvate using ALS from susceptible and resistant kochia were 2.13 and 1.74 mm, respectively. Based on these results, the mechanism of sulfonylurea resistance in this kochia biotype is due solely to a less sulfonylurea-sensitive ALS enzyme.
RESUMO
The growth characteristics of soybean (Glycine max [L.] Merr.) embryos in culture and seeds in situ were found to be similar, but developmental differences were observed. Embryos placed in culture when very small (<2 milligrams dry weight) failed to attain the maximal growth rates attained by embryos which were more mature when placed in culture. When nutrient levels were maintained in the culture medium, embryos continued to grow indefinitely, reaching dry weights far in excess of seeds matured in situ. Apparently, maternal factors were important in early and late development during the determination of maximum growth rate and the cessation of growth. Embryo growth rate was not affected by substituting glucose plus fructose for sucrose in the medium, nor by hormone treatments, including abscisic acid. Glutamine was found to give substantially better growth than glutamate, however. Contrary to prior reports, the response of soybean embryo growth rate to irradiance was found to be primarily an artifact of the effect of irradiance on media temperature. Across seven genotypes the correlation coefficient between seed growth rate in situ and embryo growth rate in vitro was 0.94, indicating essentially all of the variability of in situ seed growth rate between cultivars could be attributed to inherent growth rate differences associated with the embryos. The response to temperature was very similar for both embryos in culture and seeds in situ at temperatures below 30 degrees C. Beyond that temperature, embryo growth rate continued to increase, while seed growth rate did not. The implication is that in situ seed growth rate is determined by the inherent growth potential of the embryo at low to moderate temperatures; however, at higher temperatures, the maternal plant is unable to support the rapid growth rates that the embryo is capable of attaining under conditions of unlimited assimilate supply.
RESUMO
Establishing credentials in nursing is the subject of intense controversy and research. Decisions regarding advanced education pose more complex problems for some nurses than for others. Social changes tempt many to take for granted today's freedom of choice in life style, but persons still in very responsible and productive periods of their lives grew up in a different time. Life styles were formed under the pressures of narrower opportunities for self-esteem and social approval. Many chose to devote themselves to a combination of direct patient care and the long-term commitment of traditional family rearing. They must speak out lest their viewpoint be ignored by others whose pursuits may have gained them more verbal, organizational, and political skills.
