The use of protoplasts and separated cells in plant virus research

Signal transduction in maize and Arabidopsis mesophyll protoplasts

Plant protoplasts show physiological perceptions and responses to hormones, metabolites, environmental cues, and pathogen-derived elicitors, similar to cell-autonomous responses in intact tissues and plants. The development of defined protoplast transient expression systems for high-throughput screening and systematic characterization of gene functions has greatly contributed to elucidating plant signal transduction pathways, in combination with genetic, genomic, and transgenic approaches.

Optimisation of conditions for infection of isolated potato protoplasts with potato virus X

Conditions for the reproducible infection of potato protoplasts with PVX were determined. Successful virus infection was achieved when potato protoplasts at a concentration of 3 X 10(5) cells/ml were incubated with 20 micrograms/ml PVX and 2 micrograms/ml Poly-L-ornithine (MW 100,000) for 15 minutes at 0 degrees C. Numbers of protoplasts infected varied between 30 and 50 per cent. Preincubation of PVX with PLO for a minimum of 10 minutes was essential for good infection. The type and molecular weight of polycation used had a major effect on virus infection. PLO at 100,000 MW was the most efficient.

Plant Genetics: Increasing Crop Yield

Cell cultures of crop plants provide new opportunities to recover induced mutations likely to increase crop yield. Approaches include regulating respiration to conserve carbon fixed by photosynthesis, and increasing the nutritive value of seed protein. They depend on devising selecting conditions which only desired mutant cells can survive. Protoplast fusion offers some promise of tapping sources of genetic variation now unavailable because of sterility barriers between species and genera. Difficulties in regenerating cell lines from protoplasts, and plants from cells, still hamper progress but are becoming less severe. Recombinant DNA techniques may allow detection and selection of bacterial cell lines carrying specific DNA sequences. Isolation and amplification of crop plant genes could then lead to ways of transforming plants that will be useful to breeders.

Investigation on the infection of cucumber mesophyll protoplasts with cucumber mosaic virus

Isolated protoplasts from the first leaf mesophyll of cucumber plants have been successfully infected in vitro with cucumber mosaic virus (CMV). Virus instability before, during and after inoculation of the protoplasts resulted in low infectivities when extracts were assayed on cowpea; however, viral RNA extraction improved the bioassay technique. Attempts to optimize inoculation and incubation of protoplasts are outlined, incorporating the improved assay.

The infection of cucumber mesophyll protoplasts with tobacco mosaic virus

Protoplasts from the first leaf mesophyll of cucumber plants were isolated by an 18 hours combined petinase/cellulase treatment. Conditions favouring the infection of these protoplasts with tobacco mosaic virus (TMV), and the accumulation of infective virus up to 96 hours after inoculation have been studied. Infection of approximately 5--10 per cent of the protoplats, revealed by indirect fluorescent antibody staining, was achieved by pre-treatment of the cells in 0.01 M citrate-buffered mannitol (CBM), pH 5.2 with 2 mug/ml poly-L-ornithine followed by centrifugation and direct resuspension of the cells in the same mixture together with 2 to 4 mug/ml TMV. Higher concentrations of the polycation and buffer were toxic to the protoplasts. Under the best conditions, virus yields of approximately 10-20 mug TMV/10(6) protoplasts were attained, while after 72 hours incubation, significant amounts of virus could often be recovered from the incubation medium. Addition of actinomycin D to cultures of protoplasts 2 hours post-inoculation partially inhibited development of infectivity.

Cell concentration as a factor in precursor incorporation by tobacco leaf protoplasts or separated cells

Freshly isolated protoplasts or separated cells prepared from leaves of Nicotiana tabacum L. cvs. Xanthincor Turkish Samsun exhibit substantially greater incorporation of [(3)H] leucine and [(3)H] uridine into protoplast protein and RNA, respectively, when dilute rather than concentrated suspensions are incubated. This phenomenon is considered to result from a dilution of the labeled precursors in the incubation medium by nonlabeled precursors of cellular origin.

Ribosomal RNA metabolism in cucumber leaf mesophyll protoplasts

Aspects of the metabolism of RNA have been studied in enzymatically isolated protoplasts from cotyledon and first leaf mesophyll tissue of two cultivars of cucumber. The first leaf mesophyll protoplasts incorporated (3H)-uridine into ribosomal RNA at a constant rate for up to 25 hr in a simple salts medium and for up to 45 hr in a growth medium. Pulse-chase labelling experiments on such preparations showed a rapid dilution of the intracellular (3H)-uridine pool(s) and a high metabolic rate in the cells in one cultivar but not in another. Gel electrophoretic analysis of the RNA from both cotyledon and first leaf protoplasts showed that both protoplast types incorporated either (14C)- or (3H)-uridine into ribosomal RNA species. Incorporation of (3H)-uridine into chloroplasts RNA was minimal in cotyledon protoplasts, but significant in leaf protoplasts. Greater incorporation into the chloroplast RNA species could be achieved by longer pulses. Synthesis of all of the ribosomal RNA species was sensitive to actinomycin D at 10 and 25 mug/ml concentrations in all protoplasts tested.