Genome plasticity during the acquisition of embryogenic competence

Technique Flower Initiation
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And another oldie. The relevance is that plants regenerated from adventitious shoots (e.g., root cuttings) pass through an embryonic phase, during which the pattern of expressed/unexpressed genes can be altered, resulting in sports. ‘Happenstance’ (from Mermaid) and ‘New Dawn’ (from Dr. W. van Fleet) are examples. Such sports from Dwarf Polyanthas are too numerous to mention.

Genome/Génome 42(6): 1134-1143 (1999)
Genome plasticity during the acquisition of embryogenic competence
Chiara Geri, Alessandra Turrini, Lucia Giorgetti, Elisa Nicoletti, and Vittoria Nuti Ronchi
http://bulbnrose.x10.mx/Heredity/GeriAdvSports1999.html
Abstract: Hypocotyl explants from carrot and other species experience concomitant segregation events and differentiation of homeotic structures during the first 20 days of culture on 2,4-dichlorophenoxyacetic acid (2,4-D). In addition to these cyto-morphological changes, significant amounts of nuclear DNA are lost, the molecular details of which we investigate in this paper. We have developed a slot-blot analysis assay to study the DNA content of a series of carrot samples; besides the leaves, this survey ranged over different culture timepoints: hypocotyls, cell lines, and somatic embryo stages. We carried on to study the relationship between this DNA loss and sequence complexity modulation. Results from probing sequences that correspond to different degrees of complexity, such as medium repetitive and unique sequences as well as sequences belonging to both classes (ribosomal cistrons, ubiquitin, actin, and chalcone synthase), consistently manifested a reduction in DNA levels during the acquisition of embryogenic competence. In some cases, the cultured cells would contain only 10% of the gene copies observed in the reference tissues. Modulation trends also showed that DNA levels of most sequences recover at the torpedo-plantlet stage, which again correlates DNA modulation and the acquisition of embryogenic competence. These results suggest that similar DNA variations may occur in plants in vivo during meiosis, possibly so that meiotic division may be properly completed.

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Mol Gen Genet. 20: 246(6): 657-62. (Mar 20, 1995)
On the occurrence of somatic meiosis in embryogenic carrot cell cultures.
Giorgetti L, Vergara MR, Evangelista M, Lo Schiavo F, Terzi M, Nuti Ronchi V.
Istituto di Mutagenesi e Differenziamento CNR, Pisa, Italy.

Abstract
During the establishment of an embryogenic cell line from a carrot hypocotyl explant, processes closely resembling meiotic divisions are seen. A microdensitometric analysis revealed that the amount of cellular DNA diminished in the majority of cells to the haploid level. However, the diploid level was re-established in a matter of a few days. The genetic consequences of this segregation were studied by analyzing restriction fragment length polymorphisms (RFLP) and randomly amplified polymorphic DNAs (RAPD). The results showed that the great majority of embryos regenerated from segregants and that different segregants had different genetic constitutions.
http://bulbnrose.x10.mx/Heredity/GiorgettiSomMeios1995.html

See also Risley: Roses have satellites, too (1959)
“The number of chromosomes in the cells of one plant are supposed to be constant, and almost always are so. The full compliment of 21 chromosomes of the triploid offspring of Skinner’s Rambler x Yellow Pinocchio are shown in Figure 11. All 21 were not always present in the root-tip cells. Only 33% contained all 21, while the remainder had 20, 19, 18 and 17 chromosomes per cell. This rose should produce an occasional mutation or sport from a bud if this condition of variable chromosomes number exists in all the tissues of the plant.”
[Or if plants are regenerated from root cuttings.]

Burdick (Tomato Haploids, 1951) also observed some peculiar offspring raised from doubled haploids, including some expressing dominant traits that were not present in the original haploid.
http://bulbnrose.x10.mx/Tomato/BurdickHapTomato1951.html