Zinc allocation and re-allocation in rice.
OBJECTIVE
Agronomy and breeding actively search for options to enhance cereal grain Zn density. Quantifying internal (re-)allocation of Zn as affected by soil and crop management or genotype is crucial. We present experiments supporting the development of a conceptual model of whole plant Zn allocation and re-allocation in rice.


METHODS
Two solution culture experiments using (70)Zn applications at different times during crop development and an experiment on within-grain distribution of Zn are reported. In addition, results from two earlier published experiments are re-analyzed and re-interpreted.


RESULTS
A budget analysis showed that plant zinc accumulation during grain filling was larger than zinc allocation to the grains. Isotope data showed that zinc taken up during grain filling was only partly transported directly to the grains and partly allocated to the leaves. Zinc taken up during grain filling and allocated to the leaves replaced zinc re-allocated from leaves to grains. Within the grains, no major transport barrier was observed between vascular tissue and endosperm. At low tissue Zn concentrations, rice plants maintained concentrations of about 20 mg Zn kg(-1) dry matter in leaf blades and reproductive tissues, but let Zn concentrations in stems, sheath, and roots drop below this level. When plant zinc concentrations increased, Zn levels in leaf blades and reproductive tissues only showed a moderate increase while Zn levels in stems, roots, and sheaths increased much more and in that order.


CONCLUSIONS
In rice, the major barrier to enhanced zinc allocation towards grains is between stem and reproductive tissues. Enhancing root to shoot transfer will not contribute proportionally to grain zinc enhancement.
Department of Plant Sciences, Centre for Crop Systems Analysis, Wageningen University Wageningen, Netherlands.
Tjeerd Jan
TJ
Stomph
Crop Cultivation and Physiology Group, Shandong Key Laboratory of Dryland Farming Technology, College of Agronomy and Plant Protection, Qingdao Agricultural University Qingdao, China.
Wen
W
Jiang
Department of Plant Sciences, Centre for Crop Systems Analysis, Wageningen University Wageningen, Netherlands.
Peter E L
PE
Van Der Putten
Department of Plant Sciences, Centre for Crop Systems Analysis, Wageningen University Wageningen, Netherlands.
Paul C
PC
Struik
70Zn; Oryza sativa; re-allocation; rice; stable isotope; zinc allocation