Uptake and distribution of ⁶⁵Zn and ⁵⁴Mn in wheat grownat sufficient and deficient levels of Zn and Mn: I. During vegetative growth

The uptake and distribution of ⁶⁵Zn and ⁵⁴Mn by wheat (Triticum aestivum cv. Aroona) was investigated. Plantswere grown in a chelate-buffered 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 plants was dual-labelled with ⁶⁵Zn and ⁵⁴Mn. 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 plant was separated into leaves, main stem, unexposedroots, and tillers. In addition, the crown was separatedfrom the stem in the 14-d-old plantsIn the control plants labelled at 14 d, ⁶⁵Zn was firstdetected and accumulated in the crown of the roots after 40-60 min. Labelled Zn was then detected in the stem, followed by the leaves. The oldest and youngest leaves received less ⁶⁵Zn than the second and third oldest leaves. The plants grown under low Zn conditions accumulated more ⁶⁵Zn in their older leaves and transferred ⁶³Zn to the unexposed roots. Distribution of ⁵⁴Mn was similar in the controls to that of ⁶⁵Zn, except the older leaves received no HMn, At the second harvest, a similar distribution pattern of ⁶⁵Zn and ⁵⁴Mn was observed with regard to leaf age. Large amounts of ⁶⁵Zn and ⁵⁴Mn were detected within the unexposed roots of all treatments. It is suggested that the distribution of root-supplied Zn and Mn may be determined by micronutrient status and its relationship with leaf transpiration rates.