Zinc mobility in wheat: Uptake and distribution of zinc applied to leaves or roots

Little is known about transport of Zn from leaves to other plant organs. The present study tested a range of Zn forms applied foliarly for their suitability to provide adequate Zn nutrition to wheat (Triticum aestivum L.). Transport of Zn-65 applied either to leaves or to one side of the root system was also studied. Inorganic (ZnO, ZnSO4) and chelated sources of Zn (ZnEDTA, glycine-chelated Biomin Zn) applied foliarly provided sufficient Zn for vigorous growth. Zinc concentrations in roots and shoots were in the sufficiency range, except in the -Zn control. Foliar treatments with ZnSO4 and chelated Zn forms resulted in shoot Zn concentrations in 7-week-old plants being about two-fold greater than those in plants supplied with Zn in the root environment or via foliar spray of ZnO. Adding surfactant to foliar sprays containing chelated forms of Zn did not cause negative growth effects, but surfactant added to ZnO or ZnSO4 foliar sprays decreased shoot growth. Adding urea to the ZnO foliar spray had no effect on shoot growth. Foliarly-applied Zn-65 was translocated to leaves above and below the treated leaf as well as to the root tips. Stem girdling confirmed that Zn-65 transport reward lower leaves and roots was via the phloem. Split-root experiments showed intensive accumulation of Zn-65 in the stem and transport to all leaves as well as to the root tips in the non-labelled side of the root system. Foliar application of Zn in inorganic or organic form is equally suitable for providing adequate Zn nutrition to wheat. Phloem transport of Zn from leaves to roots was demonstrated. (C) 2001 Annals of Botany Company.