Multiple paternal genotypes in embryogenic tissue derived from individual immature loblolly pine seeds

Abstract

Pine embryogenic tissue derived from immature zygotic embryos may consist of multiple genotypes due to simple polyembryony. To test this hypothesis, megagametophytes with intact zygotic embryos were cultured from immature loblolly pine (Pinus taeda L.) seeds of clone WV42 control pollinated with a 1:1:1 pollen mix of clones WV44, WV47, and WV48. Each pollen parent contained a marker allele at one or more of the following loci: aconitase, malic dehydrogenase, 6-phosphogluconate dehydrogenase, and shikimate dehydrogenase, allowing determination of the paternal parent. After two to four weeks in culture, embryogenic tissue derived from zygotic embryos extruded from megagametophytes was separated into individual embryos and sectors of embryogenic tissue. The paternal genotype of each resulting cell line was determined by starch gel electrophoresis. Three of thirty-six explants produced multiple cell lines with genotypic differences among the cell lines within each explant. Our results unequivocally show that it is possible to initiate embryogenic tissue from more than one zygotic embryo of a loblolly pine seed and that the resulting cell lines may be genetically different.Abbreviations: ACO -aconitase, MDH -malic dehydrogenase, SKDH -shikimate dehydrogenase, 6PGD -6-phosphogluconate dehydrogenase

Somatic embryogenesis and plantlet development in Pinus sylvestris and Pinus pinaster on medium with and without growth regulators

“…Cultures of intact megagametophytes could result in an extrusion of zygotic embryos from the micropylar end. This phenomenon has been previously described in detail for P. taeda (Becwar et al 1991). The authors demonstrated that somatic embryogenesis could be initiated from more than one zygotic embryo resulting in a chimeric embryogenic cell line if multiple fertilizations took place.…”

“…In P. taeda, Gupta and Durzan (1987) suggested that somatic embryogenesis resulted from the continuation of the zygotic cleavage process. However, for the same species, Becwar et al (1991) observed a cellular proliferation before the formation of somatic embryos. In this study, no observation on the origin of the embryonal masses was made when the zygotic embryos were cultured within the megagametophytes and further histological observations are necessary to mitigate this controversy.…”

Special symposium: In vitro plant recalcitrance transcript profiling: A tool to assess the development of conifer embryos

“…This secondary growth may be stimulated by the embryo proper. Finally, pines and other conifers form welldeveloped suspensors in somatic embryogenic cultures (Jain et al, 1989;Becwar et al, 1991;Behrendt and Zoglauer, 1996) and therefore it is a straightforward matter to isolate suspensor tissue from somatic embryos. By contrast, the suspensor is often absent from somatic embryos of angiosperms or, if present, it typically lacks the features of the zygotic suspensor (Yeung and Meinke, 1993).…”

Plant physiological and genetical aspects of the somatic embryogenesis process in conifers

“…It has been suggested that the SE process in pines occurs by different mechanisms associated with the polyembryogenic process rather than a differentiation process. Indeed, it has been shown that SE cultures established from the same seed of loblolly pine (Pinus taeda) can differ genetically, indicating that more than one embryo was initiated having different fathers (Becwar et al 1991). The yields of the subsequent steps of the pine SE process are considerably lower than in most spruce species, and the complete SE process resulting in a plant is so far only successful for a limited number of clones.…”