Defensive and secondary metabolism in plant tissue cultures,with special reference to nicotinamide,glutathione and oxidative stress

The purpose of the presentation is to interconnect and illuminate certain parts of metabolism regarding stress signalling and defensive functions, including secondary metabolism in intact plants and plant tissue cultures. Increased cell/tissue levels of reactive oxygen species like H₂O₂, O₂ ^- and ·OH and the metabolism of glutathione, are linked to defensive/secondary metabolism and tissue differentiation. Special attention is paid to nicotinamide. A hypothetical role of nicotinamide and its metabolites as stress signals is also put forward especially in connection with hypomethylation of DNA. A role of DNA hypomethylation, as a link between various types of stressors and the induction of plant devensive metabolism, is discussed. We suggest that nicotinamide or nicotinamide based substances may be of value within biotechnology for the production of valuable substances as well as for plant protection.Abbreviations BSO buthionine sulfoximine - CHS chalcone synthase - GSH reduced glutathione - GSSG oxidized glutathione - INA isonicotinic acid - NIC nicotinamide - PADPRP poly(ADP-ribose)polymerase - PAL phenylalanine ammonia-lyase - SA salicylic acid - SAM S-adenosylmethionine - SSB single strand breakage