Spermine is not essential for survival of Arabidopsis

Spermine is the final product of the polyamine biosynthetic pathway and is ubiquitously present in most organisms. The genome of Arabidopsis thaliana has two genes encoding spermine synthase: ACAULIS5 (ACL5), whose loss-of-function mutants show a severe defect in stem elongation, and SPMS. In order to elucidate the function of spermine in plants, we isolated a T-DNA insertion mutant of the SPMS gene. Free and conjugated spermine levels in the mutant, designated spms-1, were significantly decreased compared with those in the wild-type, but no obvious morphological phenotype was observed in spms-1 plants. We further confirmed that acl5-1 spms-1 double mutants contained no spermine. Surprisingly, acl5-1 spms-1 was fully as viable as the wild-type and showed no phenotype except for the reduced stem growth due to acl5-1. These results indicate that spermine is not essential for survival of Arabidopsis, at least under normal growth conditions.