Herbicide resistance due to amplification of a mutant acetohydroxyacid synthase gene.

We have selected a tobacco cell line, SU-27D5, that is highly resistant to sulfonylurea and imidazolinone herbicides. This line was developed by selection first on a lethal concentration of cinosulfuron and then on increasing concentrations of primisulfuron, both sulfonylurea herbicides. SU-27D5 was tested against five sulfonylureas and one imidazolinone herbicide and was shown, in every case, to be two to three orders of magnitude more resistant than wild-type cells. The acetohydroxyacid synthase (AHAS) of SU-27D5 was 50- to 780-fold less sensitive than that of wild-type cells to herbicide inhibition. The specific activity of AHAS in the SU-27D5 cell lysate was 6 to 7 times greater than that in wild-type cells. Using Southern analysis, we showed that cell line SU-27D5 had amplified its SuRB AHAS gene about 20-fold while maintaining a normal diploid complement of the SuRA AHAS gene. Genomic clones of both AHAS genes were isolated and used to transform wild-type tobacco protoplasts. SuRB clones gave rise to herbicide-resistant transformants, whereas SuRA clones did not. DNA sequencing showed that all SuRB clones contained a point mutation at nucleotide 588 that converted amino acid 196 of AHAS from proline to serine. In contrast, no mutations were found in the SuRA clones. The stability of SuRB gene amplification was variable in the absence of selection. In one experiment, the withdrawal of selection reduced the copy number of the amplified SuRB gene to the normal level within 30 days. In another experiment, amplification remained stable after extended cultivation on herbicide-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)

[Continuous perfusion of low doses of insulin in severe diabetic decompensation (author's transl)]. / Perfusión contunua de bajas dosis de insulina en la descompensación diabética grave.

Twenty one episodes of severe uncontrolled diabetes, most of them with ketoacidosis, were treated at a Medical Intensive Care Unit with fluid and electrolyte replacement and continuous perfusion of low doses of insulin. The overall results of this therapeutic approach were a progressive and gradual return to normality of all biochemical parameters with a fall of serum glucose levels and no hypoglycemic or hypokalemic accidents. Based on this study and on a review of the literature, an updated protocol for therapy of diabetic ketoacidosis is proposed.