Polyamines in chloroplasts: identification of their glutamyl and acetyl derivatives

Incubation of chloroplasts of Helianthus tuberosus with labelled putrescine and/or spermidine and proteolytic digestion of their trichloroacetate-soluble and -insoluble proteins revealed the presence of N-(gamma-glutamyl)-putrescine, N1,N4-bis-(gamma-glutamyl)-putrescine and N1,N8-bis-(gamma-glutamyl)spermidine. This finding may be regarded as unequivocal proof of the presence of transglutaminase activity in chloroplasts. In addition, the recovery of spermidine or putrescine and acetylspermidine from chloroplasts incubated with [3H]putrescine or [3H]spermidine respectively indicates the existence of biosynthetic and oxidative pathways. These results suggest that polyamines may have an important function in chloroplasts both in their free form and by covalently binding to proteins.