Histological events leading to somatic embryo formation in cultured petioles of alfalfa

Summary An optimum 10-day exposure of petioles of alfalfa [Medicago sativa ssp.falcata (L.) Arcangeli] to 2,4-dichlorophenoxyacetic acid or 2,4,5-trichlorophenoxyacetic acid results in the semisynchronous production of somatic embryos starting about 4 days after transfer to a non-auxin-containing medium. The timing of cell division induction in the petiole explants was found to vary depending on the petiole tissue type. Cells adjacent to the vascular bundles divide first at about 48 h after exposure to auxin, closely followed by those of the inner parenchyma, whereas most of the cells of the subepidermal and epidermal layers start to divide later, between 72 and 120 h. Two different sources of callus were also evident. Cells adjacent to the vascular bundles and the inner parenchyma cells were the primary source of callus when a short, 2-day (non-embryo-producing) exposure to auxin was used. In contrast, the subepidermal and epidermal cells were the primary source of callus tissue when a longer, 10-day (embryo producing) exposure was used. It is concluded that the source of somatic embryos is primarily the daughter cells of the subepidermal or epidermal tissue or both.     

Difference of two dependent sensitivities and specificities: Comparison of various approaches

In diagnostic studies, a new diagnostic test is often compared with a standard test and both tests are applied on the same patients, called paired design. The true disease state is in general given by the so‐called gold standard (most reliable method for classification), which has to be known for all patients. The benefit of the new diagnostic test can be evaluated by sensitivity and specificity, which are in fact proportions. This means, for the comparison of two diagnostic tests, confidence intervals for the difference of the dependent estimated sensitivities and specificities are calculated. In the literature, many comparisons of different approaches can be found, but none explicitly for diagnostic studies. For this reason we compare 13 approaches for a set of scenarios that represent data of diagnostic studies (e.g., with sensitivity and specificity ?0.8). With simulation studies, we show that the nonparametric interval with normal approximation can be recommended for the difference of two dependent sensitivities or specificities without restriction, the Wald interval with the limitation of slightly anti‐conservative results for small sample sizes, and the nonparametric intervals with t‐approximation, and the Tango interval with the limitation of conservative results for high correlations.