Binding of large liposomes to plant protoplasts and delivery of encapsulated DNA

Genetic engineering for cut-flower improvement

The application of modern biotechnological approaches to cut flowers has clearly become instrumental and rewarding for the floriculture industry. In recent years, several gene-transfer procedures have been developed for some of the major commercial cut flowers. Using Agrobactrium or microprojectile bombardment, several basic protocols are now available. However, despite the great progress and interest in gene transfer to these crops, their transformation is routine in only a limited number of laboratories, and its application is still considered to be an "art form". This review summarizes the reported gene-transfer procedures for the main cut-flower crops, with an emphasis on the unique factors of each method and the recent progress in introducing new traits of horticultural interest into these species.

Physiological assay of liposome-mediated transport of a drug across Xenopus intestine: cell-liposome interaction

(1) The antagonistic effect of atropine methyl bromide entrapped in liposomes on contraction of Xenopus intestine in vitro induced by acetylcholine was studied. The results provided some insight into cell-liposome interaction. (2) Acetylcholine (0.1 mM) was added to the medium in the bath (serosal solution), while liposomes containing atropine methyl bromide in their internal and external phases were added on the mucosal side of the intestine. Large multilamellar liposomes were prepared from egg lecithin (phosphatidylcholine, PC) and cholesterol in various molar ratios. Atropine methyl bromide had most effect in liposomes composed of PC and cholesterol in a ratio of 7:3, less in those with a ratio of 4:5, and none in those with a ratio of 9:1. These effects were parallel with the sizes of these liposomes, determined by quasi-elastic light-scattering; that is, the larger the liposomes, the greater was their effect. Addition (to the liposomes) of phosphatidic acid, the negative charge of which increases the distance between the lamellar layers, increased the effect, indicating that atropine methyl bromide in the space between lamellar layers was effective. Another type of liposomes in which atropine methyl bromide was present only in the external phase of liposomes was as effective as liposomes in which atropine methyl bromide was present in both the internal and external phases. (3) From these results the following new model for liposome-mediated stimulation of transport of atropine methyl bromide is proposed. Large multilamellar liposomes have structural defects in their external lamellae through which atropine methyl bromide in the mucosal solution can penetrate into the space between the external lamellar layers and move into intestinal cells through regions of fusion between the outermost layers of the liposomes and the cell membrane.

Liposomes induce chromosome aberrations in human cultured cells

The genotoxic effect of multilamellar lipid vesicles (MLV) was analysed on cultured heteroploid and diploid human cells. Dose-dependent reduction of cell survival and mitotic rate as well as induction of chromosome aberrations were observed. Chromatid and chromosome breaks and chromatid exchanges were found in 24-h culture after liposome treatment, whereas chromosome rearrangements were prevalent at 48 h. Neutral (PC/Chol) and positive (PC/SA) MLV showed a greater damage than negative (PS/PC; PS) MLV. Fibroblasts were the most sensitive cell type. In the case of PC/Chol MLV vesicles, control experiments with PC and Chol of controlled purity ruled out the possibility that the observed chromosome aberrations were caused by toxic oxidation products present in commercial preparations.

Quantitation of the delivery of liposome contents into plant protoplasts

A procedure for the quantitation of the delivery of liposome contents into Catharanthus roseus protoplasts has been developed. The method is based on the uptake of liposome encapsulated methylumbelliferyl beta-D-glucoside and its enzymatic hydrolysis to yield fluorescent methylumbelliferone. Since the free glucoside is not taken up by the protoplasts to a significant extent, the delivery of material in the nanomole range can be measured with ease.

An ultrastructural study of the interaction of liposomes with plant protoplasts

A one-step procedure using a mixture of glutaraldehyde and osmium tetroxide was devised to fix in situ large unilamellar liposomes of phosphatidylserine for transmission electron microscopy (TEM), since the conventional fixation method was found to be inadequate in this respect. The new fixation procedure enabled us to visualize the sequence of events in the interaction of liposomes with protoplasts from Vinca rosea suspension cultures in the presence of polyethylene glycol. Liposomes were thus found adhering to the surface of protoplasts, in association with invaginating plasmalemma, and within intracellular vesicles. These observations showed that liposomes enter plant protoplasts via endocytosis. Ultrastructural profiles indicating fusion of liposomes with protoplasts were not observed.

Infection of cowpea mesophyll protoplasts with cowpea chlorotic mottle virus (CCMV) RNA encapsulated in large liposomes

It has been demonstrated that cowpea chlorotic mottle virus RNA encapsulated in phosphatidyl serine/cholesterol reverse evaporation vesicles (REV) could infect cowpea mesophyll protoplasts under conditions known to enhance liposome-protoplast interactions. Positively charged phosphatidylcholine/stearylamine multilamellar liposomes did not deliver functional CCMV RNA despite their very high nucleic acid trapping capacity and their high affinity for protoplasts.