Putrescine metabolism in a fully habituated nonorganogenic sugar beet callus and its relationship with growth

peer reviewedA fully-habituated and nonorganogenic (HNO) sugar beet callus was previously shown to overproduce polyamines, as compared with a normal (N) auxin- and cytokinin-dependent callus of the same strain. Because relationships were established between polyamine levels and metabolism with different growth and development processes, some key enzymes in the metabolic pathways of polyamines were investigated in the HNO callus, and their involvement in growth appraised. Putrescine was found to be the major free and conjugated polyamine in the HNO callus. It was biosynthesised preferentially via ornithine and ornithine decarboxylase (ODC), which is in agreement with the surplus of synthesised ornithine. Diamine (DAO) and polyamine (PAO)-oxidase activities were also highest in the HNO callus, as compared with the normal, with DAO being the more active. Transglutaminase activities (+/- Ca) were also higher in HNO than in normal callus. Addition of different polyamines or of inhibitors of their biosynthesis to the culture medium of the HNO callus modified the level of endogenous polyamines and affected callus growth. The results thus pointed out a higher polyamine metabolism, particularly of putrescine, in the actively growing auxin- and cytokinin-independent callus than in the normal one. They also provided evidence for the sensitivity of a habituated tissue type towards this class of growth regulators