Nobuyuki Kitajima

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.

Physiological and Mineralogical Properties of Arsenic-Induced Chlorosis in Barley Seedlings Grown Hydroponically

ABSTRACT The experiment was carried out to investigate the effects of arsenic (As) on the physiological and mineralogical properties of barley (Hordeum vulgare L. cv. ‘Minorimugi’). The plants were grown in nutrient solution treated with 0, 6.7, 33.5, and 67 μ M As (0, 0.5, 2.5, and 5 ppm As, respectively) in the phytotron. Dry matter yield of shoots and roots decreased significantly with the As treatments, indicating that barley plants are As-sensitive and As-toxicity depends on the As concentration in the rooting medium. Necrosis in older leaves and chlorosis symptoms (whitish color) in the fully developed young leaves were observed at the 33.5 and 67 μ M As treatments. Arsenic concentration, accumulation, and translocation increased with the increase of As concentration in the rooting medium. Arsenic was mostly concentrated in roots and a little amount was moved to shoots, indicating that As was not easily translocated to shoots of barley seedlings. Concentrations and accumulations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), zinc (Zn), and copper (Cu) decreased significantly in shoots for 33.5 and 67 μ M As treatments as compared to the 0 μ M As treatment. Concentrations of P, K, Ca, Mg, Mn, and Cu decreased in roots, but Zn concentration increased in roots at 67 μ M As treatment. Accumulations of P, K, Ca, Mg, Mn, Zn, and Cu in roots also decreased significantly at 67 μ M As treatment. Accumulation of P and the cations showed negative relationship with As. Concentration of Fe decreased in shoots at 33.5 and 67 μ M As treatments where chlorosis was induced in the young leaf but increased in roots at 33.5 and 67 μ M As treatments. It was suggested that As might induce iron (Fe)-chlorosis in the plants. Among the micronutrients, Fe translocation was more affected than others by As. Phytosiderophore (PS) accumulation in roots, which is a symptom of Fe-deficiency in grasses, did not change significantly between 0 and 33.5 μ M As treatments; indicating that As-induced chlorosis did not enhance PS accumulation in roots and decreased due to As-toxicity at 67 μ M As treatment.

Effect of arsenic on phytosiderophores and mineral nutrition of barley seedlings grown in iron-depleted medium

Abstract A hydroponic experiment with barley seedlings (Hordeum vulgare L. cv. Minorimugi) grown in iron (Fe)-depleted medium in the presence of added arsenic (As) at the rates of 0, 0.67, 6.7 and 67 µmol L−1 (equivalent to 0, 0.05, 0.5 and 5 mg L−1 As, respectively) showed that increasing the As concentration in the medium lowered the release of phytosiderophores (PS) and their concentration in the roots. This Fe-depleted experiment was conducted to clarify the effect of As on the release and concentration of PS in roots and on the phosphorus (P) and Fe concentrations in plants. The chlorophyll index increased substantially in the 67 µmol L−1 As treatment compared with the other treatments. This result indicated that higher concentrations of As might interrupt the appearance of Fe chlorosis in plants grown in Fe-depleted medium. Arsenic at a level of 67 µmol L−1 increased the Fe concentration and accumulation in shoots disappearing the whitish chlorosis. An increased concentration of Fe in the shoot might also be responsible for lowering the release and concentration of PS in the roots. Increases in the concentration of Fe in the shoot most likely resulted from enhanced Fe translocation from the roots to the shoots. The physiological mechanism of the higher Fe translocation with As needs to be investigated. Arsenic lowered the concentrations of P, potassium (K), calcium (Ca) and magnesium (Mg) in the shoot at the 67 µmol L−1 level. A higher Fe concentration and higher ratio of Fe/P in the shoot might be responsible for the greening of the leaves in the 67 µmol L−1 As treatment. The concentrations of manganese (Mn), zinc (Zn) and copper (Cu) were reduced by the high As levels. There was a concomitant increase in the As contents in shoots with higher As levels in the growth medium. The relationship between the concentrations of As and Fe and between P and Fe in the shoots was the opposite. Thus, higher As level might play a role in increasing the mobility of root Fe in barley tissues grown in Fe-depleted medium. Grasses grown under Fe-deficient conditions might not show Fe chlorosis in the presence of high concentrations of As.

Arsenic–iron interaction: Effect of additional iron on arsenic-induced chlorosis in barley grown in water culture

Abstract The effect of additional iron (Fe) on arsenic (As) induced chlorosis in barley (Hordeum vulgare L. cv. Minorimugi) was investigated. The treatments were: (1) 0 μmol L−1 As + 10 μmol L−1 Fe3+ (control), (2) 33.5 μmol L−1 As + 10 μmol L−1 Fe3+ (As-treated) and (3) 33.5 μmol L−1 As + 50 μmol L−1 Fe3+ (additional-Fe3+) for 14 days. Arsenic and Fe3+ were added as sodium-meta arsenite (NaAsO2) and ethylenediaminetetraacetic acid-Fe3+, respectively. Chlorosis in fully developed young leaves was observed in the As-treated plants. The chlorophyll index and the Fe concentration decreased in shoots of the As-treated plants compared with the control plants. Arsenic reduced the concentration of phosphorus, potassium, calcium, magnesium, manganese, zinc and copper. The additional-Fe3+ treatment increased the chlorophyll index in plants compared with the As-treated plants. Among the elements, Fe concentration and accumulation specifically increased in the shoots of additional-Fe3+ plants compared with As-treated plants, indicating that As-induced chlorosis was Fe-chlorosis. Arsenic and Fe were mostly concentrated in the roots of the As-treated plants. Despite inducing chlorosis in the As-treated plants, phytosiderophores (PS) accumulation in the roots and release from the roots did not increase, rather PS accumulation decreased, indicating that As toxicity hindered PS production in the roots. The PS accumulation in the roots was further reduced in the additional-Fe3+ treatment.

Assessing the potential of Arabidopsis halleri ssp. gemmifera as a new cadmium hyperaccumulator grown in hydroponics

Arabidopsis halleri ssp. gemmifera is a plant recently found in the heavy metal contaminated areas of Japan, and it contained a significant amount of Cd in its shoots. In this study, the potential of A. halleri ssp. gemmifera to accumulate Cd was investigated using hydroponics. The plants were grown for 21 d after Cd (control, 10, 100 and 400 µM) treatment. No reduction in shoot and root dry weight (DW) was observed when plants were grown in a nutrient solution containing up to 400 µM Cd. Cadmium concentrations in the plant parts increased significantly with Cd application rates, and reached a maximum of about 5641, 6643 and 15 967 µg g-1 in the leaves, stems and roots, respectively, at 400 µM Cd in the nutrient solution. Similarly, maximum Cd accumulation (dry weight × concentration) of 17.7 and 10.8 mg plant-1 in the shoots and roots, respectively, was obtained at 400 µM Cd. The ratio of shoot Cd/root Cd decreased with increasing rates of Cd supply from 1.8 at 10 µ M to 0.40 at 400 µM. Cadmium transloca...