Long-distance translocation of polyamines in phloem and xylem of Ricinus communis L. plants
1998
Antognoni, F. | Fornale, S. | Grimmer, C. | Komor, E. | Bagni, N.
Polyamine content and enzyme activities in the biosynthetic and degradative pathways of polyamine metabolism were investigated in sieve-tube sap, xylem sap and tissues of seedlings and adult plants of Ricinus communis L. Polyamines were present in tissues and translocation fluids of both seedlings and adult plants in relatively high amounts. Only free polyamines were translocated through the plant, as indicated by the finding that only the free form was detected in the phloem and the xylem sap. Removal of the endosperm increased the polyamine content in the sieve-tube exudate of seedlings. The level and pattern of polyamines in tissue of adult leaves changed during leaf age, but not, however, in the sieve-tube sap. Xylem sap was relatively poor in polyamines. Polyamine loading in the phloem was demonstrated by incubating cotyledons with [14O]putrescine and several unlabelled polyamines. Feeding cotyledons with cadaverine and spermidine led to a decrease in the level of putrescine in sieve-tube sap, indicating a competitive effect. Comparison of polyamine content in the tissue and export rate showed that the export would deplete the leaves of polyamines within 1-3 d, if they were not replenished by biosynthesis. Polyamine biosynthesis in Ricinus proceeds mostly via arginine decarboxylase, which in vitro is 100-fold more active than ornithine decarboxylase. The highest arginine decarboxylase, ornithine decarboxylase and diamine oxidase activities were detected in cotyledons. while in sieve-tube sap only a slight arginine decarboxylase activity was found.
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