Tobacco trichomes produce tobacco gum, which mainly consists of diterpenoids and sugar esters having organoleptic potential. We have utilized RNAi to modify the chemistry of both of these groups of gum compounds in the experimental tobacco T.I. 1068. The degree of knockdown of specific diterpenoids observed varied with all the genes manipulated from low to near complete in T0 populations, and was found to be stable in further generations, where studied. This suggests that levels/mixtures of various diterpenoids may be subject to manipulation by design. However, while in some knockdown studies results were consistent with working models that predict diterpenoid metabolic pathways in tobacco trichome glands, in other cases results appear to reveal unexpected impacts that suggest complex regulation of carbon flow in glands. The possibility that knockdown of endogenous diterpenoid metabolism may provide substrate for enzymes encoded by introduced foreign genes (e.g., diterpene synthases) is being studied.