Histocyte distribution and cadmium forms in different rice cultivar seedlings with exogenous cadmium supply

A hydroponic experiment was conducted to study cadmium (Cd) accumulation characteristics in different rice genotypes — low Cd accumulation ('D83A/R527') and high Cd accumulation ('Fuyou838'). The subcellular distribution and chemical forms of Cd in the root and shoot of different rice genotypes were investigated after exposure to Cd concentrations of 5 μmol·L^-1, 10 μmol·L^-1 and 25 μmol·L^-1. The aim of the study was to explore subcellular distribution and chemical forms change of Cd in rice to provide reference for research on Cd absorption mechanisms of rice. The results showed that: 1) the concentrations of Cd in roots and shoots and the transfer rate in 'D83A/R527' were significantly lower than those in 'Fuyou838' (P < 0.05). 2) The contents of Cd in subcellular fractions of two rice cultivars were in the orders of soluble fraction (F3) > cell wall (F1) > organelle (F2) in roots, but cell wall (F1) > soluble fraction (F3) > organelle (F2) in shoots. The proportions of Cd in cell walls (36.76%-51.75%) in both roots and shoots of 'D83A/R527' were higher than those in 'Fuyou838' (31.29%-49.07%). 3) The order of contents of Cd chemical forms revealed by different processing methods was sodium chloride extraction state (F_NaCl-Cd) > acetic acid extractable state (F_HAc-Cd) > deionized water extraction (F_W-Cd) > ethanol extracted state (F_E-Cd) > HCl extractable state (F_HCl-Cd) in both cultivars. When Cd concentration increased, the proportions of F_E-Cd and F_W-Cd (active forms) from root of 'D83A/R527' declined gradually (24.75%-18.34%), but increased gradually in 'Fuyou838' (27.18%-28.68%). The percentages of F_HAC-Cd and F_HCl-Cd (inertia forms) in shoot of 'D83A/R527' (32.41%-38.98%) were higher than those in 'Fuyou838' (28.44%-31.22%). The proportions of F_NaCl-Cd in both root and shoot of 'D83A/R527' (32.71%-51.17%) were higher than those in 'Fuyou838' (32.14%-47.63%). In short, Cd accumulation in 'D83A/R527' was lower than that in 'Fuyou838'. Then cell wall mass fractions of both root and shoot systems were higher in 'D83A/R527' than that in 'Fuyou838'. Also there was lower accumulation of active forms of Cd and higher accumulation of inertia forms of Cd in 'D83A/R527' than that in 'Fuyou838'. Therefore, rice cultivar 'D83A/R527' had a better Cd fixation capacity than 'Fuyou838'.