The development of low-alkaloid (LA) tobacco varieties is an important target in the tobacco breeding industry. However, LA Burley 21 plants, in which the Nic1 and Nic2 loci controlling nicotine biosynthesis are deleted, are characterized by impaired leaf maturation that leads to poor leaf quality before and after curing. K E Y W O R D Sethylene, inhibition of biosynthesis, maturation, nic1/nic2 mutation, nicotine, ornithine

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Treatment of tobacco (Nicotiana fabacom) cell-suspension cultures with cryptogein, an elicitin protein from Phytophfhora cryptogea, resulted in the release of a factor(s) that diffused through a 1000-D cutoff dialysis membrane and was capable of inducing sesquiterpene cyclase enzyme activity (a key phytoalexin biosynthetic enzyme in solanaceous plants) when added to fresh cellsuspension cultures. The diffusible factor(s) was released from cells over a 20-h period and induced a more rapid induction of cyclase enzyme activity than did direct treatment of the cultures with pure elicitin protein. The diffusible factor also induced a more rapid accumulation of transcripts encoding for sesquiterpene cyclase, acidic and basic chitinase, and hsr203 (a putative hypersensitive response gene) than did elicitin treatment. l h e diffusible factor(s) was resistant to protease, pectinase, DNase, and RNase treatments, was not extractable into organic solvents, and was not immunoprecipitable when challenged with polyclonal antibodies prepared against elicitin protein. The diffusible factor(s) could not induce the release of more factor, suggesting that it was a terminal signal. These results are consistent with the notion that cells directly challenged or stimulated by pathogen-derived elicitors release diffusible secondary signal molecules that orchestrate the induction of complementary defense responses in neighboring cells.

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