Genetic transformation of cereals by direct DNA delivery via microprojectile bombardment has become an established procedure in recent years. But the derivation of functional transgenic plants, especially in wheat, is still problematic, mainly due to low efficiency of DNA delivery and the reduced regeneration capability of microprojectile-bombarded tissue. We focussed on these two aspects and found that the regeneration of scutellar calli of wheat can be rendered highly efficient and considerably accelerated by a liquid culture phase in screen rafts. We also found that the expression of a reporter gene following DNA delivery by microprojectile can be improved by maintaining the scutellar calli in 0.25 M mannitol before and after bombardment, by bombardment in the presence of silver thiosulfate and Ca(NO3)2 (rather than CaCl2) and by the elimination of spermidine from the DNA/microprojectile mixture. A protocol that includes all these features leads to several-fold higher transient expression of the reporter gene than have previously published procedures.

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Antihistamine-resistant anaphylactic bronchospasm in guinea pigs is increased with increasing doses of antigen (ovalbumin, OA) challenge. This was observed in passively and actively sensitized animals, and by both i.v. and aerosol routes of antigen challenge. At a challenge concentration of 100 mg/kg OA, antihistamines were virtually inactive. Indeed, the resulting bronchospasm was inhibited by isoproterenol, theophylline and ketotifen but not any anticholinergics, anti-5HT, SRS-A antagonists, arachidonic acid lipoxygenase inhibitors or antiallergic drugs. However, in the presence of chlorpheniramine, the response was antagonized by SRS-A antagonists (FPL 55712 and isamoxole), but not the lipoxygenase inhibitors (BW 755C, ETYA, NDGA and phenidone). This suggests that the antihistamine-resistant bronchospasm produced in guinea pigs challenged with high antigen concentrations might be the result of SRS-A release. This is by no means certain since the currently available SRS-A antagonists possess other mechanisms of action; furthermore, the failure of lipoxygenase inhibitors to influence this response is not consistent with a role for SRS-A. Elucidation of the mechanism of the antihistamine-resistant bronchospasm awaits development of more specific SRS-A antagonists.