We have constructed a physical map of the human genome by using a panel of 90 whole-genome radiation hybrids (the TNG panel) in conjunction with 40,322 sequence-tagged sites (STSs) derived from random genomic sequences as well as expressed sequences. Of 36,678 STSs on the TNG radiation hybrid map, only 3604 (9.8%) were absent from the unassembled draft sequence of the human genome. Of 20,030 STSs ordered on the TNG map as well as the assembled human genome draft sequence and the Celera assembled human genome sequence, 36% of the STSs had a discrepant order between the working draft sequence and the Celera sequence. The TNG map order was identical to one of the two sequence orders in 60% of these discrepant cases.
We present evidences that ultrastructural electron microscope findings are valuable ways to understand the in vitro regeneration process, in particular in the yellow passion fruit. Shoot-regeneration was induced in hypocotyl and leaf-derived explants using 4.44 lM BAP, and the entire organogenic process was analyzed using conventional histology, scanning and transmission electronic microscopy. Both direct and indirect regeneration modes were observed in hypocotyl explants, but only direct regeneration occurred in leaf-derived cultures. In the direct pathway from both explant types, meristemoids developed into globular structures, here called protuberances. The peripheral meristematic layers of the protuberances displayed ultrastructural characteristics indicative of a high metabolic activity, and only these cells originated shoots and leaf primordia, the latter being frequent when leaf explants were used. Moreover, the peripheral cells of the protuberances derived from leaf explants lost adhesion during the culture, diminishing the regeneration rates. We recommend the use of hypocotyls as a source of explant to obtain shoots as well as a genetic transformation system for the yellow passion fruit. However, the direct pathway is preferred because a type of amitosis occurred in the peripheral cells of hypocotyl-derived calli, which has the potential to result in genetic instability of the regenerating plants/tissue.
A comparative anatomical analysis of somatic embryogenesis in two soybean (Glycine max (L.) Merrill) genotypes was carried out. The somatic embryos were originated from cotyledonary explants obtained from immature zygotic embryos. The medium used for somatic embryogenesis induction was Murashige and Skoog, 1962, salts and Gamborg et al., 1968, vitamins (MSB) supplemented with 0.8 mg.L-1 of 2,4-D for genotype PI 123439 and 40 mg.L-1 of 2,4-D for ‘Williams 82’. Globular structures, constituted by meristematic cells, originated from subepidermal cell divisions of the cotyledonary mesophyll. In PI 123439, the globular structures presented tracheary differentiation among meristematic cells and they could follow distinct morphogenetic process depending on their location along the explant. For ‘Williams 82’ it was observed globular structures along the cotyledonary explant surface. They gave rise to somatic embryos. These embryos showed different morphologies and they were classified based on their shape and number of cotyledons. The ability of these morphological types to convert to plantlets was discussed.
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