Isolation and Characterization of Carrot Cell Mutants Resistant to α-Amanitin

Gene-expression programs in embryogenic and non-embryogenic carrot cultures

Somatic embryogenesis can be synchronized by enriching carrot (Daucus carota L.) suspension cultures for small, dense clusters of cells termed proembryogenic masses (PEMs). Gene-expression programs of PEMs were compared with those of embryonic and mature tissues by in-vitro translation of representative mRNA populations and by nucleic-acid hybridization. Analysis of invitro-translated polypeptides by two-dimensional polyacrylamide gel electrophoresis revealed striking similarities between the mRNA populations of PEM and torpedo-stage embryos; substantial differences, however, were observed when in-vitro translation products of PEMs and torpedo embryos were compared with those of hypocotyls and leaves. Northern blots of RNA isolated from PEMs, staged embryos, and mature carrot tissues were hybridized with cDNA probes for Dc3, Dc5 and Dc13; these cDNA recombinants represent mRNAs that are regulated during carrot somatic embryogenesis. The pattern of expression of these embryo-regulated transcripts was similar in PEMs and somatic embryos but differed in other carrot tissues. These results indicate that many of the molecular processes of embryogenesis are already established in PEMs in the presence of auxin. Additional experiments indicate the utility of Dc3 as a molecular marker for the acquisition of embryogenic potential.

Ethanol production and toxicity in suspension-cultured carrot cells and embryos

The process of carrot (Daucus carota L.) somatic embryogenesis is highly sensitive to exogenously added ethanol, since 5 mM ethanol inhibits this process by 50%, whereas the growth of proliferating carrot cells is inhibited to the same extent by 20 mM ethanol. This is consistent with the fact that proliferating cultures produce ethanol and release it into the medium at concentrations up to 20 mM, whereas embryogenic culture medium contains less than 1 mM ethanol. Data are presented showing the influence of cell density and 2,4-dichlorophenoxyacetic acid on ethanol production and on the presence of an alcohol-dehydrogenase (EC 1.1.1.1.) inactivator in carrot embryos.

Role of permanent dicentric systems in carrot somatic embryogenesis

A permanent dicentric chromosome system was studied on carrot cultures and regenerated somatic embryos at different stages of development. The large chromosomal variability of the cultures and the presence of the breakage-fusion bridge cycle did not interfere with the initial developmental process up to the seedling stage but subsequent growth proceeded only if healing of the broken ends or dicentric loss had occurred. The behaviour of the dicentric chromosome in culture and during somatic embryogenesis is discussed in relation to chromosomal variability, abnormal development and the somaclonal variation that such mechanisms may generate in regenerated plants.

High plating efficiency with plant cell cultures

In this paper we describe a simple method to improve the plating efficiency in plant cell cultures.Two-stage plating is used; in the first stage the cells are inoculated at high density in 0.2% agarized culture medium for ten days to facilitate growth; under this condition, each cell produces a single micro-colony trapped in the agar network. In the second stage the colonies are plated at different densities in 1% agarized medium.These colonies are self-sufficient and able to improve the cell growth by conditioning the medium.

Stimulation of carrot somatic embryogenesis by proline and serine

Serine and proline, when added in a wide range of concentrations to Daucus carota cultures during pre-growth in the presence of 2,4-D(2,4-dichlorophenoxyacetic acid), extended in time and quantity the mitotic divisions and stimulated significantly the number of embryos regenerated when the hormone subsequently was omitted from the medium. A specific effect of these amino acids on regeneration is suggested, since proline (as hydroxyproline) and serine are the two major constituents of the cell wall glycoprotein, extensin, which thus may have a morphoregulatory function. The significant role of the conditions during pregrowth of the cultures in the presence of hormone is underlined by the effect of hydroxyproline and D-proline which also stimulate embryogenesis, but alter markedly the development of the embryos.

Isolation and developmental characterization of temperature-sensitive carrot cell variants

Carrot cell lines multiply indefinitely in the presence of the auxin 2,4-D. If auxin is removed, the cells regenerate plantlets in a process that closely resembles embryogenesis in vivo. We isolated a temperature-sensitive variant, ts 2, which is unable to regenerate at 31 °C (non-permissive temperature), but does form embryos and plants at 24 °C (permissive temperature). The temperature treatment had no effect on fully differentiated ts 2 plantlets. In other variants (ts 5 and ts 11) cell proliferation was inhibited at the restrictive temperature. These lines were leaky with respect to the inhibition of embryogenesis at 31 °C.

Analysis of the heat-shock protein pattern during somatic embryogenesis of carrot

The pattern of proteins synthesized by carrot cells after heat-shock was analyzed by SDS-polyacrylamide gel electrophoresis. A study was made of the time of appearance and disappearance of the heat-shock bands and a comparison was made of the heat-shock proteins present in cell extracts obtained from cell suspensions, callus, protoplasts and the different stages of somatic embryogenesis.From this comparison a number of differences and hence of stage-specific markers could be seen. This type of analysis was also carried out in the presence of α-amanitin in order to get information on the type of control of heat-shock protein synthesis. It turned out that in all stages after the initial globular stage, α-amanitin does not alter the heat-shock protein pattern suggesting pre-existence of the relative mRNA's.

A new method for the purification of the different stages of carrot embryoids

An easy method is presented for the purification of the different stages of carrot embryoids. This is based on a synchronization of the regenerating culture and on a filtration through filters of various pore sizes. A differential sedimentation was used for removing undifferentiated cells. At the end of the process, the different stages: globular, heart- and torpedo-shaped were obtained with a degree of purity that always exceeded 90%. This method can be used for the separation of relatively large numbers of embryoids (from thousands to a million) of haploid and diploid carrot lines and is very gentle on embryoids in that it does not affect their viability or further development.