DISTRIBUTION AND REMOBILIZATION OF ZN AND MN DURING GRAIN DEVELOPMENT IN WHEAT

Wheat (Triticum aestivum cv, Aroona) was grown in siliceous sand with essential nutrients for unlimited growth except for the following treatments: controls (sufficient Zn and Mn), low Mn (sufficient Zn) and low Zn (sufficient Mn) until anthesis, Replicate plants were harvested at anthesis; the remaining plants were transferred to a chelate-buffered nutrient solution containing ail essential nutrients except Zn and Mn to allow monitoring of the remobilization of existing Zn and Mn reserves within the plant. These plants were harvested 14 d post-anthesis and at grain maturity, At each harvest plants were separated into individual components. There were no growth differences between any of the treatments at the three harvests. Large amounts of Zn and Mn found in the roots and stems at anthesis were rapidly depleted during grain development. The Zn content of the leaves increased from anthesis to 14 d post-anthesis, but then declined. The Mn content of the leaves increased throughout grain development in the controls whilst remaining constant in the plants pre-grown at low Mn. The Zn and Mn content of the glumes, palea and lemma rose in the controls from anthesis to 14 d post-anthesis; thereafter Zn content declined but Mn content continued to increase, The Zn and Mn content of the grain rose sharply toward grain maturity. We conclude that Mn was not remobilized from the leaves of wheat during grain development, Zinc was remobilized from the leaves, especially the flag leaf and from the leaves of the low Zn plants. The post-anthesis accumulation of Zn and Mn within the glumes will be discussed in relation to the transport pathway that Zn and Mn use to enter the developing seed.