DNA binding and uptake by nuclei isolated from plant protoplasts: factors affecting DNA binding and uptake

Liposome-mediated delivery of tobacco mosaic virus RNA into tobacco protoplasts: A sensitive assay for monitoring liposome-protoplast interactions

Tobacco mosaic virus (TMV) RNA was encapsulated in large, unilamellar phospholipid vesicles (liposomes), and the encapsulated TMV RNA was shown to be infectious when incubated with tobacco protoplasts under appropriate conditions. Maximal virus production in protoplasts was observed after their incubation with TMV RNA entrapped in phosphatidylserine/cholesterol liposomes. Infection was dependent on the presence of polyalcohols in the incubation mixture. Other parameters, such as the extent of vesicle binding, the cell-induced leakage of vesicle contents, and the degree of liposome toxicity were shown to be important in determining the efficiency of infectivity. Liposome-mediated delivery offers an efficient and reproducible method for introducing RNA into plant protoplasts.

Uptake and binding of cytoplasmic DNA by wheat embryo cell nuclei

Cytoplasmic non-mitochondrial DNA was selectively labelled and isolated In a linear single-stranded form from early wheat embryos. The isolated preparation was readily taken up by wheat embryo cell nuclei and firmly bound to large, chromosome-like structures. Similarly prepared nuclear DNA fragments, although taken up, remained unbound and underwent a rapid degradation within the cell nuclei. The selective binding of the cytoplasmic DNA indicates that it might be integrated into the nuclear genome.

Liposome-mediated delivery of tobacco mosaic virus RNA into petunia protoplast : Improved conditions for liposome-protoplast incubations

Liposome-mediated delivery of TMV RNA into petunia protoplasts and resulting virus antigen production has been used as an assay for determining incubation conditions which favor increased uptake of vesicle contents by plant cells. Vesicle phospholipid composition, incubation buffer divalent metal ion concentration, the type and concentration of polyalcohol used to stimulate vesicle uptake and the RNA content of the liposome preparation were determined to be critical factors influencing the efficiency of delivery. Manipulation of these parameters resulted in a 50-fold improvement in virus antigen production over that obtained with conditions previously used for liposome-protoplast incubations (Proc Natl Acad Sci 79: 1859-1863, 1982). Virus antigen production could be detected following incubation of protoplasts with <0.5 ng of encapsulated TMV RNA, while at higher concentrations of added liposomes, >80% of the protoplasts could be infected. Comparisons with other techniques used to introduce nucleic acids into plant protoplasts indicated that liposome-mediated delivery was 10-to 1 000-fold more efficient than these other methods. The general use of liposomes to introduce RNA and DNA molecules into plant protoplasts is discussed.

DNA Binding and Uptake by Nuclei Isolated from Plant Protoplasts: Fate of Single-stranded Bacteriophage fd DNA

Binding and uptake of exogenous DNA by nuclei isolated from Glycine max L. Merr were studied using (3)H-labeled single-stranded DNA of bacteriophage fd. A comparison of single-stranded with double-stranded DNA for binding and uptake by nuclei was also made.Isolated nuclei were incubated with (3)H-labeled single-stranded bacteriophage fd DNA. Poly-l-lysine or DEAE-dextran at 0.1 and 1 mug/ml stimulated DNA binding. On the other hand, poly-l-lysine at 1 and 5 mug/ml increased DNA uptake but DEAE-dextran did not. Ten to 20 mm Ca and Mg ions were required for DNA uptake. EDTA (1-20 mm) did not differ from the control or the low levels of Ca or Mg ions. These observations on single-stranded fd DNA differed from those obtained with double-stranded DNA of Salmonella typhimurium. Kinetics of single-stranded DNA binding and uptake also deviated from that of double-stranded DNA.Analyses of nuclei-bound DNA by sucrose density gradient and CsCI density gradient centrifugation revealed extensive DNA degradation during a 45-minute incubation period. Poly-l-lysine protected against rapid degradation of bound DNA. DEAE-dextran enhanced DNA binding, but bound DNA was cleaved into much smaller polymers than those detected in control experiments or in the presence of poly-l-lysine. Sucrose density gradient and CsCI density gradient centrifugation analyses on DNA taken up by nuclei also showed extensive DNA degradation. Poly-l-lysine slightly inhibited DNA degradation, but DEAE-dextran appeared to enhance degradation of incorporated DNA. Moreover, nonbound DNA in the incubation medium was completely degraded within a 20-minute incubation period.