The effect of polyamines on leaf senescence in two diverse rose speciesN

Polyamines (PAs) retarded the senescence of leaf discs of two diverse species of rose viz., Rosa bourboniana and Rosa damascena, while polyamine biosynthetic inhibitors difluoromethylornithine (DFMO), difluoromethylarginine (DFMA), methylglyoxal-bis (guanylhydrazone) (MGBG) and abscisic acid (ABA) promoted senescence. Spermine was significantly the most effective polyamine in retarding senescence in R. bourboniana while MGBG and DFMA were more prominent in accelerating senescence in R. damascena and R. bourboniana respectively. Protein and RNA content were significantly higher in polyamine treated leaf discs compared to those treated with polyamine biosynthetic inhibitors and ABA. Total and reducing sugars decreased under all treatments while the starch content increased significantly only in polyamine treated leaf discs. Peroxidase and cellulase activities were retarded by polyamine treatments and accelerated by polyamine biosynthetic inhibitors and ABA. The role of PAs is discussed in relation to senescence