An efficient plating system for rapid isolation of mutants from plant cell suspensions

Patterns of protein synthesis in dividing and auxin-starved soybean cell suspensions. Differential expression of a major group of Mr-17000 peptides

Auxin starvation of soybean cell suspensions results in the arrest of cell growth after about 4 days. The addition of 4 μM 2,4-D enables cells to divide again after a lag phase of 1 day. By comparing the patterns of in vivo and in vitro protein synthesis, we have identified two sets of polypeptides whose synthesis is positively or negatively regulated by auxin. Several major peptide bands (17, 26, 31, 35, 38 kD) are characteristic of auxin-starved cells. The 17 kD peptide group, containing one major (75%) component, accounts for 6% and 25% of the radiolabeling in vivo of proteins from respectively dividing and auxin-starved cells. Our results suggest the 17 kD major component to be a direct translation product whose synthesis is regulated by the abundance or the activity of the relevant mRNA. The soybean suspension culture system here described provides a model to study auxin-mediated control of gene expression.

Changes in methylation of tissue cultured soybean cells detected by digestion with the restriction enzymes HpaII and MspI

Each of the tandemly arranged 5S RNA genes of soybean contain two CCGG sites which, if unmethylated, can be digested by both MspI and HpaII. Methylation of the internal cytosine (CmeCGG) prevents digestion by HpaII but allows digestions by MspI.Suspension cultures were prepared from soybean plants and the DNA from these cultures was examined for the susceptibility of 5S RNA genes to digestion by MspI and HpaII. 5S genes from DNA extracted from intact plants can be partially digested with MspI but not at all by HpaII. In contrast, shortly after cells were cultured the 5S RNA could be hydrolyzed by both HpaII and MspI. After prolonged cell culture, the 5S genes from some cell lines were found to have become partially or even completely resistant to HpaII digestion. The results suggest that lack of methylation can occur when cells are cultured and that such methylation may play a role in the heritable changes observed in cell culture.

High cytotoxicity and membrane permeability of Et3Pb+ in mammalian and plant cells

Cells of mammalian origin as well as those of higher plants appear to be very sensitive to triethyllead ion (Et3Pb+). Neuroblastoma cells kept in the presence of 1 microM Et3Pb+ lost their viability within 6 h. Growth of suspension culture cells of soybean (G. max(L.)Merr.) was inhibited by 1 microM Et3Pb+, and finally the cells died. Morphologically, Et3Pb+ caused the complete breakdown of microtubular structures in neuroblastoma cells; thus microtubules appeared to be the main target for the toxin. While in a previous study the effect of Et3Pb+ on microtubules has been well documented at concentrations of 50-200 microM 1, the present study demonstrates that the formation of microtubules from pig brain tubulin is disturbed at concentrations of Et3Pb+ as low as 0.5 to 1 microM. We conclude from these data that Et3Pb+ freely permeates the plasma membranes of mammalian as well as plant cells.

Isopropyl-N(3-chlorophenyl) carbamate (CIPC) induced chromosomal loss in soybean: a new tool for plant somatic cell genetics

The properties and uses of tissue culture partial haploid soybean cell lines are explored. Partial haploid lines were prepared by CIPC treatment of a genetic heterozygote, and compared to this heterozygote and to homozygous cell lines corresponding to the parental genotypes from which the heterozygote was derived. Cell lines which lack chromosomes were characterized physiologically and with respect to a variety of isozyme markers. Often the loss of chromosomes revealed a phenotype corresponding to a recessive parental genotype. In some cases, however, new phenotypes were observed indicating a complex genotype and suggests the interaction of several genes. The implications of this for plant breeding are discussed.CIPC also was used as a tool to dissect a complex phenotype which arose as the result of mutagenesis. A mutant cell line which required asparagine for growth but also had acquired the ability to grow on allantoin as a sole source of nitrogen was treated with CIPC to remove chromosomes. The requirement for asparagine could be separated from the ability to use allantoin, demonstrating that these phenotypes were the result of separate mutations.

Isolation of an auxotrophic cell line of soybean (Glycine max) which requires asparagine or glutamine for growth

A suspension culture of haploid soybean cells was treated with ultra-violet light. From the mutagenized culture an auxotrophic cell line was isolated which grows on 1-B5 media supplemented with asparagine or glutamine. In the absence of these additives the cells cease to grow and die. Asparagine is unable to serve as a sole source of nitrogen, i.e., cannot substitute for nitrate and ammonia.

Isolation of sodium dependent variants from haploid soybean cell culture

Following ultraviolet mutagenesis, we have isolated two Na(+) dependent variants from haploid suspension cultures of soybean cells. No selection was used in the isolation procedure. These cells cannot grow in 1 mM Na(+) but can grow in 17 mM Na(+). The strains also grow in 33 or 65 mM Na(+), concentrations in which the parent cell line dies. [(22)Na] was used to measure the accumulation of Na(+) by parent and variant cell lines. Two- to three-fold less Na(+) is retained by the variant cell lines.

Nutritional requirements of protoplast-derived, haploid tobacco cells grown at low cell densities in liquid medium

Preliminary attempts to define a completely synthetic medium able to support divisions of haploid tobacco mesophyll protoplasts at low initial densities have failed. High protoplast concentrations together with large amounts of naphtaleneacetic acid in the medium (3 mg l(-1) NAA) were required for maximal induction of protoplast division. However, cell suspensions derived from haploid protoplasts after four days of preculture at high initial cell densities could be diluted to densities as low as 1-4 cells ml(-1), provided the concentration of NAA in the medium was lowered to below 0.3 mg l(-1). The optimal NAA supply for low cell density growth was affected by the nature of the nitrogen source.A simple minimal medium which supports the growth of these haploid cells with a plating efficiency of 30-40%, independent of the cell density in the range of 1-4 to 3·10(4) cells ml(-1), has been established. In this medium inositol was the only vitamin stringently required for growth.Growth of cells at low densities was also possible in a medium initially containing 3 mg l(-1) NAA, provided it was conditioned by the growth of protoplasts at high densities. Preliminary experiments with [(14)C]NAA showed that the amount of free NAA remaining in the medium after preincubation at high densities was drastically reduced. Simultaneously, NAA conjugates accumulated in the medium. The implications of these results are discussed.