# Visualizing the distribution of various inorganic metals in brown rice by radiotracer experiments

## TL;DR

This study uses radiotracer experiments to visualize how different inorganic metals are distributed in brown rice grains.

## Contribution

The study introduces a direct injection method to reduce costs and enables 3D visualization of metal distribution in rice.

## Key findings

- 63Ni distributes uniformly in the endosperm early on but accumulates in outer layers and embryo later.
- 203Hg entry into embryonic tissue is restricted regardless of rice grain development stage.
- Autoradiography with Imaging Plates allows high-throughput 3D reconstruction of metal distribution.

## Abstract

The distribution of inorganic elements in brown rice has been vigorously investigated for many years using the most advanced instruments of each era. The present study was a challenge to gain new insights into the distribution of various inorganic elements in brown rice by autoradiography using radioisotopes: 22Na, 45Ca, 54Mn, 55Fe, 60Co, 63Ni, 65 Zn, 90Sr, 203 Hg, and 210 Pb. Autoradiography of tissue sections using the Imaging Plate (IP) fully exploited its advantage of high-throughput imaging, enabling three-dimensional reconstruction that encompassed the entire brown rice grain. Consequently, characteristic distribution patterns of individual elements in the peripheral layer, endosperm, and embryo were identified following radiotracer supplementation to the culture solution. For instance, 63Ni was uniformly distributed within the endosperm during the early stages of development but progressively accumulated in the outer layers and embryo as growth advanced; such a pattern was not observed for 54Mn or 55Fe. To minimize the cost of the experiment, a direct injection method into the node was developed. This approach successfully visualized 203 Hg, demonstrating that its entry into the embryonic tissue is severely restricted irrespective of the developmental stage of the rice grain.

Graphical Abstract