Subcellular Distribution of Cadmium in Two Paddy Rice Varieties with Different Cooking Methods

Abstract

Cadmium (Cd) is a non-essential element that is highly mobile within organisms where, following plant uptake, subcellular distribution plays an important role in plant tolerance and detoxification. Cd uptake and subcellular distribution were studied in two paddy rice varieties (Japonica and Indica) hydroponically cultivated in Cd-containing solutions. Japonica rice grains containing Cd were also collected from a Cd-contaminated site and subjected to various cooking treatments (boiled, stir-fried, steamed, and control) to determine the influence of cooking method on the subcellular distribution of Cd. Cd treatment inhibited both shoot height and root length, especially in Japonica, where for the same Cd treatment, Japonica accumulated more Cd in roots and shoots than Indica. Most of the accumulated Cd (92% - 99%) was bound to the cell wall and vacuoles, and decreased in the order: soluble fraction (Fs) > cell wall fraction (Fcw) > organelle fraction (Fco). Subcellular Cd concentrations in rice grains were significantly affected by cooking treatment. The proportion of trophically available Cd decreased with increase in cooking duration and temperature, indicating that consuming steamed and stir-fried rice had a lower Cd exposure risk than consuming boiled rice.