PHLOEM TRANSLOCATION OF STRONG ACIDS GLYPHOSATE, SUBSTITUTED PHOSPHONIC AND SULFONIC-ACIDS IN RICINUS-COMMUNIS L

The mobility in phloem of several substituted phosphonic acids and a s ulfonic acid was studied in the castor bean plant, Ricinus communis L. For a series of C-14-labelled phosphonate mono-esters applied to the petioles of mature leaves, phloem transport was modest, becoming poor over longer distances in the plant. Substituted phenylphosphonic acids were more efficiently moved in phloem; uptake from the petiole and su bsequent redistribution were slow, but these dibasic compounds were ve ry stable in plants and substantial amounts reached the roots after 72 to 120 h. Glyphosate was very efficiently transported to phloem sinks even within 24 h, with high concentrations in phloem sap. Toluene-4-s ulfonic acid moved predominantly in the xylem to the mature leaves and its phloem transport was poor. Transport patterns are considered in r elation to the physico-chemical properties of the compounds. Ion trapp ing appears to play little part in the phloem transport of these stron g acids, though the good accumulation and transport in phloem of the c omplex molecule glyphosate cannot at present be explained.