Zinc allocation and re-allocation in rice
Stomph, T.J. ; Jiang, W. ; Putten, P.E.L. van der; Struik, P.C. - \ 2014
Frontiers in Plant Science 5 (2014). - ISSN 1664-462X - 12 p.
developing wheat grains - aerobic rice - soil-zinc - zn - biofortification - remobilization - translocation - micronutrients - fertilization - nutrition
Aims: 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 70Zn 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.
Does increased zinc uptake enhance grain zinc mass concentration in rice?
Jiang, W. ; Struik, P.C. ; Keulen, H. van; Zhao, M. ; Jin, L.N. ; Stomph, T.J. - \ 2008
Annals of Applied Biology 153 (2008)1. - ISSN 0003-4746 - p. 135 - 147.
developing wheat grains - deficient calcareous soils - human-nutrition - aerobic rice - hypercholesterolemic men - micronutrient density - edible portions - blood-pressure - phytic acid - brown rice
Rice (Oryza sativa) is the worlds' most important cereal and potentially an important source of zinc (Zn) for people who eat mainly rice. To improve Zn delivery by rice, plant Zn uptake and internal allocation need to be better understood. This study reports on within-plant allocation and potential Zn accumulation in the rice grain in four so-called aerobic rice cultivars (Handao297, K150, Handao502 and Baxiludao). Two controlled-condition experiments were carried out, one with a wide range of constant Zn concentrations in the medium and one with a range of plant growth rate-related supply rates. In both experiments, increased Zn supply induced increased plant Zn uptake rate throughout crop development, when expressed as daily Zn uptake (¿g day¿1) or as daily Zn uptake per gram of plant dry matter (¿g g¿1). Zinc mass concentration (ZnMC) in all plant organs increased with an increase in Zn supply but to various degrees. At higher uptake levels, the ZnMC in stems increased most, while the ZnMC in hulled grains (brown rice) increased least. The increase in leaf ZnMC was generally small, but at toxic levels in the medium, leaf ZnMC increased significantly. It appears that regulation of grain Zn loading differs from regulation of Zn loading to other organs. A milling test on seeds of Baxiludao and Handao502 showed that when ZnMC in brown rice increased from 13 to 45 mg kg¿1, ZnMC in polished rice grains (endosperm) also increased from 9 to 37 mg kg¿1 but remained three to five times lower than that in the bran. Irrespective of the ZnMC in the brown rice, around 75% of total grain Zn was present in the endosperm. In both cultivars, there was a major difference in ZnMC between bran and endosperm (120 and 37 mg kg¿1, respectively), suggesting a barrier for Zn transport between the two tissues. There seems to be a second barrier between stem and rachis, as their ZnMCs also differed greatly (300 and 100 mg kg¿1, respectively) in both cultivars at higher plant ZnMC. It is concluded that there is too little scope from a human nutrition perspective to enhance ZnMC in rice endosperm by simply increasing the Zn supply to rice plants because Zn allocation to the endosperm is limited, while observed genotypic differences indicate scope for improvement through breeding.
Uptake and distribution of root-applied or foliar-applied 65Zn after flowering in aerobic rice
Jiang, W. ; Struik, P.C. ; Lingna, J. ; Keulen, H. van; Ming, Z. ; Stomph, T.J. - \ 2007
Annals of Applied Biology 150 (2007)3. - ISSN 0003-4746 - p. 383 - 391.
developing wheat grains - zinc uptake - zn - plants - accumulation - manganese - iron - cu - phytoremediation - nutrition
We investigated the uptake and distribution of zinc (Zn) either applied to the roots or to the leaves in rice during grain development. Plants of two aerobic rice cultivars were grown in a nutrient solution with either sufficient Zn or surplus Zn. Root treatment with 1 week`s supply of both 65Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with 65Zn applied to the flag leaf or to senescent leaves was carried out at flowering. When 65Zn was applied to roots, plants continued to take up Zn after flowering, even beyond 15 DAF, irrespective of cultivar and Zn nutritional status of the plants. During the 1 week of supply of both 65Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed 65Zn was mainly distributed to roots, stem and grains. Little 65Zn was allocated to the leaves. Following a week of 65Zn supply directly after flowering, under sufficient Zn or surplus Zn, the proportions of total 65Zn uptake allocated to the grains continued to change during grain filling (9¿33%). This Zn mainly came from the roots but under sufficient Zn supply also from the stem. With 65Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both cultivars showed similar Zn distribution within the plants. About 45¿50% of the 65Zn absorbed was transported out of the 65Zn-treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was partitioned to the panicle parts and even less to the grains. These results suggest that in rice plants grown under sufficient or surplus Zn supply, most of the Zn accumulated in the grains originates from uptake by roots after flowering and not from Zn remobilisation from leaves