Chemical forms of chromium in rice plants: does this fraction determine its phytotoxicity?

Chemical forms of chromium (Cr) in rice seedlings ( Oryza sativa  L. cv. BX139) exposed to either potassium chromate Cr(VI) or chromium nitrate Cr(III) were clarified using a hydroponic study. Seven chemical fractions of Cr in different rice tissues were extracted using a sequential extraction method. Results indicated that exposures to both Cr valents resulted in significant accumulation of Cr in rice tissues and Cr(III) was more bioavailable for rice seedlings than Cr(VI). However, Cr chemical forms were inconsistent in both plant materials (root/shoots) as well as in two different Cr variants. Although both Cr variants caused dose-dependent inhibition on relative growth rates of rice seedlings, different inhibition mechanisms most likely exited using a partial correlation analysis. Both fractions of Cr in cell wall and in intracellular location in roots significantly inhibited the relative growth rates of rice seedlings exposed to Cr(VI), while inhibition of the relative growth rate of rice seedlings exposed to Cr(III) was largely stemmed from Cr partition in intracellular fraction in shoots.