Synthesis of the flavour precursor, alliin, in garlic tissue cultures.

The path of synthesis of alkyl cysteine sulphoxides, or flavour precursors, in the Alliums is still speculative. There are two proposed routes for alliin biosynthesis, one is from serine and allyl thiol while the other is from glutathione and an allyl source via gamma glutamyl peptides. The routes have been investigated by exposing undifferentiated callus cultures of garlic and onion to potential pathway intermediates. After a period of incubation of 2 days the callus was extracted, and analysed for flavour precursors and related compounds by HPLC. Standards of alliin, isoallin and propiin were synthesised and their identity confirmed by HPLC and NMR. Putative intermediates selected included the amino acids serine and cysteine, as well as more complex intermediates such as allylthiol, allyl cysteine and glutathione. Both garlic and onion tissue cultures were able to synthesize alliin following incubation with allylthiol, and cysteine conjugates such as allyl cysteine. The ability of the tissue cultures to form alliin from intermediates was compatible with the proposed routes of synthesis of alliin.

Electrofusion of plant cells.

Isolated plant protoplasts can be induced to fuse with protoplasts from different species and, therefore, provide an ideal system for genetic modification and for use in plant breeding. Techniques for electrofusion of plant protoplasts have been developed relatively recently, and specialized apparatus is required, although this is now becoming more widely available. Electrofusion offers definite advantages over more commonly used protocols that make use of chemical stimulation to induce fusion. The most valuable aspects of electrofusion techniques are the high fusion frequencies attained, often tenfold higher than analogous chemical systems (1). The use of potentially toxic chemical stimulants is avoided, and the zones of membrane disturbance are limited to regions of membrane contact alone, all of which tends to preserve protoplast viability. Additionally, fusion events can be monitored microscopically, allowing the precise determination of the effects of various electrical parameters and, therefore, the use of optimum electrical values. Such control, together with manipulation of electrodes, allows more precise definition of parentage (2) than previously was possible with other methods.

Dual fungal and plant cell culture.

Plant tissue cultures are now well-recognized as valuable experimental systems for use in the study of host-pathogen interactions. These techniques have obvious major advantages for the examination of obligately biotrophic fungi and also those with a necrotrophic life style, and it is in these areas that much research effort has been concentrated (1). Success with combined fungal-plant cultures has been variable, especially in terms of establishing cultures that may be maintained in a balanced state for prolonged periods, but there is no doubt that such systems are useful places for the study of cell-cell interactions.

Electrofusion of protoplasts from celery (Apium graveolens L.) with protoplasts from the filamentous fungus Aspergillus nidulans.

A method was developed for electrofusion of higher-plant protoplasts from celery and protoplasts from the filamentous fungus Aspergillus nidulans. Initially, methods for the fusion of protoplasts from ecch species were determined individually and, subsequently, electrical parameters for fusion between the species were determined. Pronase-E treatment and the presence of calcium ions markedly increased celery protoplast stability under the electrical conditions required and increased fusion frequency with A. nidulans protoplasts. A reduction in protoplast viability was observed after electrofusion but the majority of the protoplasts remained viable over a 24-h incubation period. A small decline in protoplast respiration rate occurred during incubation but those celery protoplasts fused with A. nidulans protoplasts showed elevated respiration rates for 3 h after electrofusion.

Metal tolerance in tissue cultures of anthoxanthum odoratum.

Tissue cultures were initiated from one non-tolerant (S20) and two zinc and lead tolerant (T92 and T94) clones of Anthoxanthum odoratum. Growth of callus from the non-tolerant clone was reduced by the presence of zinc, lead, copper and nickel, whereas callus from the two tolerant clones showed no reduction of growth in the presence of zinc and lead but growth was reduced by copper and nickel. The specificity of metal tolerance shown by the parental material was maintained in the callus. Tolerant and non-tolerant callus accumulated similar amounts of zinc and lead.