Regulation of zinc and manganese transport into developing wheat grains having different zinc and manganese concentrations

Grains of wheat were produced with differing zinc (Zn) or manganese (Mn) co ntents by culturing detached ears from anthesis onwards in solutions of fou r different concentrations of Zn or Mn (0.1, 1.0, 10, and 50 mu M). After 2 0 days, ears were labeled with Zn-65 or Mn-54 at (i) the pretreatment conce ntrations of Zn or Mn, or (ii) at 10 mu M Zn or Mn regardless of the pretre atment. Accumulation of Zn or Mn in the grain was greater as the pretreatme nt concentration of Zn or Mn increased from 1.0 to 10 mu M, however, accumu lation was less in ears cultured at 50 mu M Zn or Mn. Accumulation of Mn in grain of different Mn status labeled at 10 mu M Mn was similar in the 0.1, 1.0, and 10 mu M Mn pretreatments, but accumulation in the grain pretreate d at 50 mu M Mn was reduced. In contrast, accumulation of Zn in grains of d ifferent Zn status when labeled at 10 mu M Zn was highest in ears pretreate d at 10 mu M Zn, but substantially lower in ears of a lower Zn status (thos e pretreated at 0.1 or 1.0 mu M Zn) as well as in those preheated at 50 mu M Zn. These results suggest that Zn-deficient grain was not a strong sink f or Zn, while at high concentrations of solution Zn, a protective barrier ex ists preventing excessive accumulation of Zn in the grain. Proportionally m ore Zn was distributed to the inner pericarp and generally less to the endo sperm, outer pericarp, and embryo as the Zn status of the grain increased. This work demonstrates that loading of Zn and Mn into, and distribution wit hin, wheat grain is regulated by the nutritional status of the grain.