On the bonding of manganese, copper and cadmium to peptides of the xylem sap of plant roots

Abstract

In the xylem sap of pumpkin roots peptides or peptide similar compounds of M (molecular weight) up to 10,000 were established. The bonding of Mn, Cu and Cd to specific peptide fractions was investigated in root exudates of beheaded pumpkin roots. Fractionation of exudate peptides by gel filtration indicates that Mn is spread all over the peptides. Copper is only found with peptides of M about 1,400 to 5,000. Cadmium is coupled with the same peptide fractions up to M 5,000. The amino acid composition of Cd- and Cu-peptides indicates a higher content of cysteine. Rising nitrate nutrition of the plants resulted in low increases of Mn transport rates and in strong ones of Cu. The substitution of NO₃ ⁻ by NH₄ ⁺ as the only N source of the plants brought about a drastically increased peptide content in the exudate followed by reduced exudation volumes as well as Mn transport rates and followed by unaffected rates of Cu transport.