RESEARCH ARTICLE Uptake and distribution of root-applied or foliar-applied 65 Zn after flowering in aerobic rice W. Jiang 1,2 , P.C. Struik 2 , J. Lingna 3 , H. van Keulen 4,5 , Z. Ming 6 & T.J. Stomph 2 1 Crop Cultivation and Physiology Group, Laiyang Agricultural University, Qingdao, China 2 Crop and Weed Ecology Group, Wageningen University, Wageningen, The Netherlands 3 Crop Cultivation and Physiology Group, Yangzhou University, Jiangsu, China 4 Plant Production Systems Group, Wageningen University, Wageningen, The Netherlands 5 Plant Research International, Wageningen University and Research centre, Wageningen, The Netherlands 6 Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing, China Keywords Grain quality; nutrient distribution; nutrient uptake; Oryza sativa zinc. Correspondence P.C. Struik, Crop and Weed Ecology Group, Wageningen University, PO Box 430, 6700 AK Wageningen, The Netherlands. Email: paul.struik@wur.nl Received: 21 December 2006; revised version accepted: 25 February 2007. doi:10.1111/j.1744-7348.2007.00138.x Abstract 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 65 Zn and unlabelled Zn was started at flowering or 15 days after flowering (DAF). Foliar treatment with 65 Zn applied to the flag leaf or to senescent leaves was carried out at flower- ing. When 65 Zn 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 65 Zn and unlabelled Zn, which either started at flowering or 15 DAF, the absorbed 65 Zn was mainly distributed to roots, stem and grains. Little 65 Zn was allocated to the leaves. Following a week of 65 Zn supply directly after flowering, under suffi- cient Zn or surplus Zn, the proportions of total 65 Zn 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 65 Zn applied to leaves (either the flag leaf or the lowest senescent leaf), both culti- vars showed similar Zn distribution within the plants. About 45–50% of the 65 Zn absorbed was transported out of the 65 Zn-treated leaf. From that Zn, more than 90% was translocated to other vegetative organs; little was parti- tioned 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. Introduction Zinc (Zn) is an essential micronutrient for plants (Barak & Helmke, 1993) and human beings (Buyckx, 1993). Important basic plant processes affected by Zn include photosystem II activity, carboxylation and energy dissi- pation. Zn deficiency may even cause photodamage (Monnet et al., 2005). Moreover, Zn is an essential com- ponent of thousands of plant proteins (Broadley et al., 2007). Zn deficiency in soils is common in many parts of the world, including the rice-growing areas of India (Karak et al., 2006) and China (Gao et al., 2006). Zn defi- ciency in the soil can be remedied by Zn fertiliser sup- ply either applied through the roots or through the leaves. Crop responses to Zn fertiliser can be substantial (Broadley et al., 2007). Annals of Applied Biology ISSN 0003-4746 Ann Appl Biol 150 (2007) 383–391 ª 2007 The Authors Journal compilation ª 2007 Association of Applied Biologists 383