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Physiology and modelling of zinc allocation in aerobic rice

  • Jiang, W.
Publication Date
Jan 01, 2008
Wageningen University and Researchcenter Publications
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Keywords: Zinc, rice, Oryza sativa, grain, Zn mass concentration, biofortification Zinc (Zn) deficiency in humans is widespread in many regions of the world, especially in the developing world. Rice, the staple food of more than half of the world’s population, is potentially an important source of Zn for people whose diet consists mainly of cereal grain. Therefore, this thesis aimed at exploring the allocation of Zn in rice plants, as a basis for establishing the potential for enhancing their grain Zn mass concentration (ZnMC). Two solution culture experiments, covering wide ranges in Zn supply levels, showed that increased Zn supply resulted in increased plant Zn uptake throughout crop development and in higher ZnMC in all plant organs, but to varying degrees. With higher plant Zn uptake, ZnMC increased most in stems, and least in grains. Two apparent barriers for Zn transport were identified, one between stem and rachis and one between bran and endosperm, since their ZnMCs strongly differed at high plant ZnMC. Using radioactive 65Zn applied to root or leaf after flowering, we found that when rice plants were grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originated from uptake by roots after flowering, rather than from Zn remobilised from leaves. On the basis of the results of the above studies on Zn (re-)allocation in rice plants, and derived relations between Zn mass fractions in different organs, we developed a descriptive simulation model to increase quantitative understanding of the relevant processes involved in grain zinc accumulation. Results from an independent field experiment were used for model validation. Results showed that the model allowed reproduction of recognizable patterns of ZnMC for a wide range of absolute values, and simulated grain ZnMC was in satisfactory agreement with observed values, with a mean normalized gross error of 8–11%. Further testing under different conditions is necessary to build confidence in its general applicability. To assess genotypic variation in grain ZnMC, we proposed two new indices: low-Zn tolerance index for grain yield (TIY) and grain Zn mass concentration (TIZnMC). We found TIY and TIZnMC effective in identifying genotypes that perform well in terms of yield and grain ZnMC, respectively, under both Zn-limited and Zn-sufficient conditions. It is concluded that there is limited scope for enhancing ZnMC in rice endosperm by simply increasing the Zn supply to rice plants, not enough to attain values necessary from a human nutritional point of view, because zinc allocation to the endosperm is limited, while observed genotypic differences indicate scope for improvement through breeding. .

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