Physiological and mineralogical properties of arsenic-induced chlorosis in rice seedlings grown hydroponically
2006
SHAIBUR, Molla Rahman | KITAJIMA, Nobuyuki | SUGAWARA, Reiko | KONDO, Toshihito | HUQ, S.M Imamul | KAWAI, Shigenao
A hydroponic experiment was conducted to observe the effect of arsenic (As) on a number of physiological and mineralogical properties of rice (Oryza sativa L. cv. Akihikari) seedlings. Seedlings were treated with 0, 6.7, 13.4 and 26.8 μmol L⁻¹ As (0, 0.5, 1.0 and 2.0 mg As L⁻¹) for 14 days in a greenhouse. Shoot dry matter yield decreased by 23, 56 and 64%; however, the values for roots were 15, 35 and 42% for the 6.7, 13.4 and 26.8 μmol L⁻¹ As treatments, respectively. Shoot height decreased by 11, 35 and 43%, while that of the roots decreased by 6, 11 and 33%, respectively. These results indicated that the shoot was more sensitive to As than the root in rice. Leaf number and width of leaf blade also decreased with As toxicity. Arsenic toxicity induced chlorosis symptoms in the youngest leaves of rice seedlings by decreasing chlorophyll content. Concentrations and accumulations of K, Mg, Fe, Mn, Zn and Cu decreased significantly in shoots in the 26.8 μmol L⁻¹ As treatment. However, the concentration of P increased in shoots at 6.7 and 13.4 μmol L⁻¹ As levels, indicating a cooperative rather than antagonistic relationship. Arsenic and Fe concentration increased in roots at higher As treatments. Arsenic translocation (%) decreased in the 13.4 and 26.8 μmol L⁻¹ As treatments compared with the 6.7 μmol L⁻¹ As treatment. Arsenic and Fe were mostly concentrated in the roots of rice seedlings, assuming co-existence of these two elements. Roots contained an almost 8-16-fold higher As concentration than shoots in plants in the As treatments. Considering the concentration of Mn, Zn and Cu, it was suggested that chlorosis resulted from Fe deficiency induced by As and not heavy-metal-induced Fe deficiency.
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