UPTAKE AND DISTRIBUTION OF ZN-65 AND MN-54 IN WHEAT GROWN AT SUFFICIENT AND DEFICIENT LEVELS OF ZN AND MN .2. DURING GRAIN DEVELOPMENT

We investigated the uptake and distribution of Zn and Mn in wheat during grain development. Plants were grown in a chelate-buffered nutrient solution with one of the following treatments: control, low Zn or low Mn. Plants were dual-labelled with Zn-65 and Mn-54 at 2 and 8 wk post-anthesis for 5 and 24 h, respectively, After labelling, the plants were separated into individual components for analysis. In the plants harvested at 8 wk after anthesis, spikelets were separated into individual structures and analysed for radioactivity. Little or no root-supplied Mn-54 was distributed to the leaves of both the controls and low-Mn plants during the grain development stages studied here, More Mn-54 Was distributed to the head at 8 wk than at 2 wk post-anthesis. In contrast, root-supplied Zn-65 was transported to the leaves at 2 and 8 wk post-anthesis. More Zn-65 was distributed to the leaves of the low-Zn plants than the controls during grain development, More Zn-65 was detected in the head towards grain maturity. Relatively larger amounts of Mn-54 than Zn-65 were found in different parts of the florets, Labelled Mn was found in relatively large quantities in the palea, lemma and in the glumes, even though most Mn-54 was found in the grain, A large percentage of the grain Mn-54 was in the outer pericarp. During grain development leaves may still require Zn but not Mn, which may be due to the requirement of Zn in maintaining membrane structure and function. Distribution of Zn and Mn within the spikelets suggests that Zn may enter the grain via the phloem while Mn may enter the grain via the xylem.