PHLOEM TRANSLOCATION OF FE, CU, MN, AND ZN IN RICINUS SEEDLINGS IN RELATION TO THE CONCENTRATIONS OF NICOTIANAMINE, AN ENDOGENOUS CHELATOR OF DIVALENT METAL-IONS, IN DIFFERENT SEEDLING PARTS

During the first 8 days of germination the Ricinus seedling is supplied with all nutrients by the endosperm via phloem transport. In 4- to 8-days-old seedlings the concentrations and contents of Fe, Cu, Mn and Zn, and nicotianamine (NA) in the endosperm, cotyledons, hypocotyl and roots were estimated. From the data obtained translocation rates and flow profiles for the metals were established. The main sink for Fe, Mn and Zn were the cotyledons whereas Cu was mainly imported into the hypocotyl. Maximum flow rates occurred between days 5 and 7, for Zn between days 6 and 8. The time kinetics of NA and divalent metal ion concentrations and contents are interpreted as co-transport. The role of NA as transport vehicle of micronutrients in the sieve tubes is discussed.