LONG-DISTANCE TRANSLOCATION OF POLYAMINES IN PHLOEM AND XYLEM OF RICINUS-COMMUNIS L. PLANTS

Polyamine content and enzyme activities in the biosynthetic and degrad ative pathways of polyamine metabolism were investigated in sieve-tube sap, xylem sap and tissues of seedlings and adult plants of Ricinus c ommunis L., Polyamines were present in tissues and translocation fluid s of both seedlings and adult plants in relatively high amounts. Only free polyamines were translocated through the plant, as indicated bs; the finding that only the free form was detected in the phloem and the xylem sap. Removal of the endosperm increased the polyamine content i n the sieve-tube exudate of seedlings. The level and pattern of polyam ines in tissue of adult leaves changed during leaf age, but not, howev er, in the sieve-tube sap. Xylem sap was relatively poor in polyamines . Polyamine loading in the phloem was demonstrated by incubating cotyl edons with [O-14]putrescine and several unlabelled polyamines. Feeding cotyledons with cadaverine and spermidine led to a decrease in the le vel of putrescine in sieve-cube sap, indicating a competitive effect. Comparison of polyamine content in the tissue and export rate showed t hat 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 arginin e decarboxylase. ornithine decarboxylase and diamine oxidase activitie s were detected in cotyledons, while in sieve-tube sap only a slight a rginine decarboxylase activity was found.