UPTAKE AND DISTRIBUTION OF ZN-65 AND MN-54 IN WHEAT GROWN AT SUFFICIENT AND DEFICIENT LEVELS OF ZN AND MN .1. DURING VEGETATIVE GROWTH

The uptake and distribution of Zn-65 and Mn-54 by wheat (Triticum aest ivum cv, Aroona) was investigated. Plants were grown in a chelate-buff ered nutrient solution with either sufficient Zn and Mn, low Zn or low Mn. A single representative seminal root from 14-d-old and 42-d-old p lants was dual-labelled with Zn-65 and Mn-54. The 14-d-old plants were harvested every 10 min from 10-140 min of labelling, whilst the 42-d- old plants were harvested after 2 h of labelling, At harvest, each pla nt was separated into leaves, main stem, unexposed roots, and tillers. In addition, the crown was separated from the stem in the 14-d-old pl ants. In the control plants labelled at 14 d, Zn-65 was first detected and accumulated in the crown of the roots after 40-60 min. Labelled Z n was then detected in the stem, followed by the leaves, The oldest an d youngest leaves received less Zn-65 than the second and third oldest leaves, The plants grown under low Zn conditions accumulated more Zn- 65 in their older leaves and transferred Zn-65 to the unexposed roots. Distribution of Mn-54 was similar in the controls to that of Zn-65, e xcept the older leaves received no Mn-54. At the second harvest, a sim ilar distribution pattern of Zn-65 and Mn-54 was observed with regard to leaf age. Large amounts of Zn-65 and Mn-54 were detected within the unexposed roots of all treatments, It is suggested that the distribut ion of root-supplied Zn and Mn may be determined by micronutrient stat us and its relationship with leaf transpiration rates.