Physiological and mineralogical properties of arsenic-induced chlorosis in rice seedlings grown hydroponically

Abstract

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.

Arsenic Toxicity in Akitakomachi Rice in Presence of Fe3+-Edta

“…Similar trends were also found for the width of leaf blade and leaf number. In this experiment we did not see any new tiller (Shaibur et al, 2006).…”

“…The chlorotic symptoms appeared this time (June-July, 2007) were not as conspicuous as it was in the previous time (August-September; Shaibur et al, 2006). Chlorotic symptoms seem to be clearer in warmer season at 13.4 µM As exposure (August-September; Shaibur et al, 2006) because the growth was higher and Fe concentration might be diluted in the young leaves. At sunlight, seedlings were curled at 26.8 and 33.5 µM As levels and the turgidity decreased with the increasing As and sunlight intensity.…”

“…Solution was renewed every week and was not aerated. The detailed methodology has been described earlier (Shaibur et al, 2006) with some exception. The experiment was carried out in the greenhouse of Iwate University, Japan, with ambient light (roughly 14 hours day/10 hours night).…”

“…Arsenic was measured by using Hydride Generation Atomic Absorption Flame Emission Spectrophotometer. Determination of chlorophyll index, calculation for the parameters and statistical analysis were described elsewhere (Shaibur et al, 2006;Shaibur and Kawai, 2010).…”

“…Ingestion of As can occur through As-contaminated food material especially green leafy vegetable spinach (Ahmad et al, 1999;Farid et al, 2003;Anawer et al, 2002;Shaibur and Kawai, 2010) and water spinach (kalmi; Farid et al, 2003;. Recently, we showed that sodium meta-arsenite (NaAsO 2 ) in the rooting medium could induce whitish chlorotic symptom in the young leaves of Akihikari rice variety (Shaibur et al, 2006) -EDTA and we did this experiment in hydroponic system.…”