Inhibition of deoxyribonuclease activity in the medium surrounding plant protoplasts

Deoxyribonuclease inhibitors

Deoxyribonucleases (DNases) are a class of enzymes able to catalyze DNA hydrolysis. DNases play important roles in cell function, while DNase inhibitors control or modify their activities. This review focuses on DNase inhibitors. Some DNase inhibitors have been isolated from various natural sources, such as humans, animals (beef, calf, rabbit and rat), plants (Nicotiana tabacum), and microorganisms (some Streptomyces and Adenovirus species, Micromonospora echinospora and Escherichia coli), while others have been obtained by chemical synthesis. They differ in chemical structure (various proteins, nucleotides, anthracycline and aminoglycoside antibiotics, synthetic organic and inorganic compounds) and mechanism of action (forming complexes with DNases or DNA). Some of the inhibitors are specific toward only one type of DNase, while others are active towards two or more. Physico-chemical properties of DNase inhibitors are calculated using the Molinspiration tool and most of them meet all criteria for good solubility and permeability. DNase inhibitors may be used as pharmaceuticals for preventing, monitoring and treating various diseases.

Inhibition of deoxyribonuclease activity associated with soybean chloroplasts

The effects of spermidine, pH, ethylene diamine tetracetic acid (EDTA), and adenosine triphosphate (ATP) on deoxyribonuclease (DNase) activity associated with the chloroplasts of soybean (Glycine max (L.) Merr.) were investigated. Chloroplast DNase activity was found to be partially inhibited by either 10 mM spermidine, 20 mM EDTA, or 20 mM ATP. DNase activity was also partially inhibited at non-neutral pH's. Nearly complete inhibition was achieved with use of 30 mM EDTA, pH 10, or a combination of 10 mM spermidine and 10 mM EDTA.

Relationship between Vital Staining and Subculture Growth during the Senescence of Plant Tissue Cultures

The vital staining properties of rose cultures (Rosa cv Paul's Scarlet) of increasing age were compared with their ability to be subcultured. At 4-day intervals beginning on day 14, after cell division and expansion had stopped, cells were stained separately with Evans blue, fluorescein diacetate, and phenosafranine. The degree to which parent cultures stained with each of these dyes was compared to the dry weight of their subcultures harvested after 9 and 21 days of growth.Staining with either Evans blue or fluorescein diacetate was demonstrated to be a good means of establishing when senescing cells died. However, the staining properties of aging cultures did not correlate well with their ability to be subcultured, because an increasing proportion of the living cells appeared to lose their ability to divide as senescence progressed.

Liposome-mediated delivery of DNA to carrot protoplasts

The encapsulation of DNA within liposomes and subsequent fusion of the liposomes with carrot (Daucus carota L.) protoplasts were examined to determine optimum conditions for effective liposome-mediated delivery of DNA to protoplasts. Escherichia coli [(3)H]DNA could be encapsulated with 50% efficiency using encapsulation volumes as low as 0.5 ml. Incorporation of liposome-encapsulated [(3)H]DNA by carrot protoplasts increased linearly for 2.5 h, and increasing the ratio of protoplasts to liposomes increased the total amount of radioactive label incorporated within the protoplasts. Liposome-mediated incorporation of [(3)H]DNA by protoplasts increased over a range of polyethylene glycol concentrations up to 20%, but Ca(2+) did not increase liposome-mediated incorporation when present in the liposome-protoplast incubation mixture. Optimum incorporation was observed when the pH of the liposome-protoplast incubation medium was decreased to 4.8. Encapsulation experiments using DNA of the plasmid pBR322 indicated that an average of 200-1,000 intact copies of pBR322 were sequestered within each nucleus after liposome delivery.

An improved procedure for the isolation and purification of protoplasts from carrot suspension culture

A procedure is reported for the rapid and highly reproducible isolation of protoplasts from carrot suspension culture. The method utilizes Onozuka R 10 cellulase which has been purified by chromatography on Sephadex G75. Protoplast isolation, using this procedure, is quantitative and complete within 1 to 1.5 h. Intact protoplasts were separated from broken ones and other cellular debris by application of a polyethylene glycol/dextran two-phase system. The protoplasts isolated in this manner lack any detectable cell wall and are greater than 95% viable when assayed using fluorescein diacetate. It is concluded that such protoplasts are highly suitable for biochemical studies.

Entrapment of plasmid DNA by liposomes and their interactions with plant protoplasts

Lecithin and lecithin/cholesterol liposomes formed in aqueous solutions of DNA entrap covalently closed circular, open circular and linear DNA molecules of size up to at least 13 kilobases. The sequestered DNA molecules are efficiently protected against exogenous deoxyribonuclease action although nicking and linearization of circular DNA can be observed. The size of these liposomes ranges from approximately 0.5 to 7.5 mu with an average of 2.5--4 mu. DNA filled liposomes strongly interact with plant protoplasts under conditions inducing protoplast fusion. Results suggest that sequestered plasmid DNA can be transferred to protoplast nuclei.

Liposome-Mediated transfer of bacterial RNA into carrot protoplasts

The uptake of liposome-encapsulated E. coli [(3)H]RNA by carrot (Daucus carota L.) protoplasts was examined. [(3)H]RNA extracted from protoplasts that had been incubated with [(3)H]RNA-containing, large, unilamellar lipid vesicles (liposomes) obtained by ether infusion, and examined by sucrose gradient centrifugation and formamide-polyacrylamide gel electrophoresis, appeared substantially degraded, with a total elimination of 23S RNA and a partial loss of 16S RNA. In contrast, no breakdown of the [(3)H]RNA was apparent in the liposomes after sequestration, even in the presence of externally added ribonuclease, or in the unfused liposomes remaining after incubation of protoplasts with liposomes. Thus, the degradation of the [(3)H]RNA extracted from the protoplasts must have occurred within the protoplasts and represents evidence for liposome-mediated RNA uptake. Naked RNA added to the protoplast culture was found to be totally degraded after incubation with the protoplasts. The uptake of liposome-sequestered RNA by protoplasts was demonstrated to be a function both of the lipid composition of the liposomal membrane and of the temperature of incubation of the liposomeprotoplast mixture. Furthermore, the mode of this uptake (fusion versus endocytosis) could be manipulated by adjusting the cholesterol content of the liposomal membrane. The implications of the ability to insert RNA into protoplasts without degradation by extracellular nucleases are discussed.