Isotopic fractionation of zinc in field grown tomato

Many of the world's soils are deficient in zinc (Zn), and this has implications for plant and human nutrition. Consequently, there is a need to better understand plant uptake and allocation of Zn. Natural abundances of stable isotopes have been used to gain insight into uptake, assimilation, and allocation of various elements by plants. Inductively coupled plasma mass spectrometry was used to study the fractionation of Zn isotopes in the shoots and fruits of mature tomato plants (Solanum lycopersicum L.) grown on an organic farm. Effects of mycorrhizal colonization of roots on Zn fractionation were studied by growing a tomato mutant with reduced mycorrhizal colonization, and its mycorrhizal wild-type progenitor. Fruits of both genotypes were enriched in ⁶⁴Zn and ⁶⁶Zn and depleted in ⁶⁷Zn and ⁶⁸Zn isotopes, based on calculations that expressed the concentration of each isotope as a percentage of total Zn. The reverse was true of the shoots. Furthermore, shoots of the mycorrhizal genotype were very slightly enriched in ⁶⁴Zn and ⁶⁶Zn isotopes relative to those of the reduced mycorrhizal colonization genotype. Possible explanations for fractionation of Zn between shoots and fruits, including differential bonding of Zn to cellular components, processes affecting Zn-phytate-protein complexes, and Zn transport and translocation processes are discussed.