Putrescine accumulation in maize roots treated with spermidine: evidences for spermidine to putrescine conversion

Exogenous spermidine applied to maize seedlings through the roots increases the endogenous putrescine titer of primary roots during the first hour of treatment. The putrescine increase was due neither to a transfer from bound and conjugated pools into the free form nor to de novo synthesis. When 1 mM ['4C]spermidine was added to the growth medium, endogenous putrescine contained 44% of the total 14C detected in the dansylated fraction after 18 h of treatment. Treatment with 1 mM spermine labelled with [14C]spermine gave ['4C]spermidine and ['4C]putrescine. After treatment of maize seedlings with ['4C]y-aminobutyraldehyde, a degradation product of spermine and spermidine, no radioactivity was detected in endogenous putrescine, which excludes the hypothesis that degradation products are involved in putrescine synthesis. Up to now the biochemical steps of the interconversion pathway were unknown.