THE PLANT-CELL WALL IS ALTERED BY INHIBITION OF POLYAMINE BIOSYNTHESIS

Polyamines (PAs) and the cell wall have important roles in plant morph ogenesis. An interaction between cell wall components (pectic substanc es) and polyamines is known and inhibition of polyamine biosynthesis i nduces inhibition of some morphogenic processes. This is the case of r hizogenesis in tobacco (Nicotiana tabacum L.) thin layers. This paper investigates whether inhibition of polyamine biosynthesis induces modi fications in the structure, shape and size of the primary cell walls i n tobacco thin layers cultured on a rhizogenic medium, and whether pol yamines (putrescine and spermidine) administered in combination with t heir corresponding inhibitors DL-alpha-difluoromethylornithine + DL-al pha-difluoromethylarginine (DFMO + DFMA), cyclohexylamine (CHA), methy lglyoxal-bis(guanylhydrazone) (MCBG) restore cell wall characteristics . In treatments with polyamine inhibitors, cell hypertrophy occurred i n the lowermost layer of the explant in contact with the medium. Many unusual features were observed in the walls of the hypertrophic cells: an amorphous structure, loosening of the fibrillar component; detachm ent between contiguous cells, lysis of wall components and an uneven t hickness often giving a wavy appearance (in transverse walls). The inh ibitors reduced cell wall thickness, and caused a weak positive PATAg reaction for polysaccharides. Polyamines restored cell wall thickness and, in general, the other wall features. Our results show that polyam ines are necessary for maintaining cell wall characteristics by streng thening the links between cell-wall components.