Sub-Cellular Distribution of Zinc in Different Vegetative Organs and Their Contribution to Grains Zinc Accumulation in Rice Under Different Nitrogen and Zinc Supply

Zinc is an important micronutrient for the growth and development of human body and plants. Proper use of nitrogen fertilizer and foliar application of Zn have been proven to be important agronomic measures to improve zinc accumulation and biofortification in rice grains. However, little is known about the physiological mechanism of remobilization of Zn and characteristics of its subcellular distribution in source organs in response to N/Zn supply. In this study, the distribution of Zn at subcellular level in rice stem-sheaths, leaves, and glumes and their apparent contribution rates were examined; and the accumulation mechanism of Zn in rice grains was further explored. Zn concentration and accumulation, especially the contribution rate of stem-sheaths (43.47%) were higher than that of leaves (12.46%) and glumes (11.13%), indicating the stem-sheaths may be the main organs of Zn storage in rice. The proportions of Zn in soluble fraction in three vegetative organs were increased under N topdressing and N/Zn combined treatment and thus enhances the ability of Zn transportation from these organs to grains. In addition, Zn concentration of brown and milled rice could be increased by applying Zn fertilizer on panicles (ZnS, N + ZnS), which suggests the possibility of applying agronomic measures to enhance Zn translocation from vegetative organs to grains, thus to improve the accumulation of Zn in rice grain.