Co-ordinated inhibition of squalene synthetase and induction of enzymes of sesquiterpenoid phytoalexin biosynthesis in cultures of Nicotiana tabacum

摘要: Abstract Treatment of log-phase cell suspension cultures Nicotiana tabacum with the biotic elicitor cellulase completely inhibited cellular growth within a few hours and caused rapid accumulation sesquiterpenoid phytoalexins capsidiol debneyol. Acetosyringone (an unrelated phenolic compound) was also produced by elicited cultures. Capsidiol levels fell to low concentrations after period had ceased whereas level debneyol maintained that acetosyringone bi-phasic. Growth resumed 24 hr paralleled control When or were supplied unelicited they rapidly catabolized levels. Elicitor treatment catabolism three but did not affect metabolism A cell-free preparation obtained from cells 12 elicitation efficiently catalysed formation two uncharacterised sesquiterpenoids (one which [unknown I ] may be an eremophilane hydrocarbon) when incubated either [1- 14 C]IPP 3 H 2 ]FPP as substrate. In presence NADPH O , system amount unknown being proportionately reduced. None above biosynthetic capabilities present in extracts cells. The total radioactivity incorporated into capsidiol, unknowns provided indirect estimate activity FPP-carbocyclase, enzyme catalysing first committed step biosynthesis these compounds. time course rate synthesis preparations showed detectable cellulase. Thereafter, both rose maximum for each phytoalexin preceding its accumulation. II at all points elicitation. Squalene synthetase (EC 2.5.1.21) underwent decline over six remained until about 48 hr. apparent K m values (FPP substrate) squalene debneyol, 10, 2, 12, 10 μm respectively.The inhibition operate channel FPP away sterol (which is required growth) towards FPP-carbocyclase involved part more general response plant elicitors. accumulated lower than those capsidiol. These differences are thought due inhibitory effect on results indicate co-ordinated sequence changes involving regulation several enzymic activities occurs tobacco upon Studies have wider implications other eukaryotic systems.