The conversion of spermidine to putrescine and 1,3-diaminopropane in the roots of Limonium tataricum

Abstract

Spermidine degradation has been studied in Limonium tataricum because it was suspected to be involved in β-alanine and β-alanine betaine biosynthesis, the typical betaine of this species. When supplied to the root medium of L. tataricum seedlings, spermidine was absorbed and accumulated especially in the roots, while the amount of spermidine in the shoots slightly increased. This indicates either a poor translocation of the triamine to the shoots or a high rate for its degradation at this level. In the roots of spermidine-treated plants, 1,3-diaminopropane and putrescine levels increased possibly relying on two different pathways for spermidine degradation. In response to incubating in the presence of spermidine, 1,3-diaminopropane accumulated in the external medium to a much higher extent than putrescine. Pulse-chase experiments performed with [1,4- 14C]-spermidine demonstrated the expected conversion of this amine to spermine in the roots. In addition, the labelling of putrescine and γ-aminobutyric acid indicated the interconversion of spermidine into putrescine, itself further oxidised to γ-aminobutyric acid. Pulse-chase experiment using [1,4- 14C]-putrescine showed that this amine was more rapidly translocated to the shoots than spermidine and that it was metabolized to spermidine, spermine and γ-aminobutyric acid in these organs. Our data related to the polyamine profiles of the roots of seedlings supplied with spermidine and those showing the release of 1,3-diaminopropane to the external medium suggested that two different polyamine oxidases could be involved in the spermidine degradation in the roots of L. tataricum. According to their ability to generate 1,3-diaminopropane or putrescine, they could be located in the apoplast or in the symplast of the roots, respectively.