Shigeru Kamei

Amelioration of manganese toxicity in barley with iron

The ameliorating effect of additional iron (Fe) on manganese (Mn) toxicity in barley (Hordeum vulgare L. cv. Minorimugi) was evaluated using 1/2-strength modified Hoagland-Arnon nutrient solution. Manganese toxicity (2.50 μM Mn) was expressed as reduced dry matter yield, redistribution of growth, mild interveinal chlorosis on younger leaves, brown spots on older leaves and stems, phytosiderophore (PS) release from roots, and gradual desiccation of older leaves and root browning. The PS released from roots of plants was identified, using high-performance liquid chromatography (HPLC), as mugineic acid. Application of additional Fe (100 μM) to Mn stressed plants fully counteracted Mn-induced Fe deficiency symptoms, recovered total dry matter yield partially, and changed the plants composition and accumulation of essential mineral nutrients. The Mn critical toxicity levels in shoots and roots of Mn stressed plants with 10.0 μM Fe, expressed by reduced growth, were 44 and 147 μg g− 1 dry matter, respectively. The Mn concentrations in shoots and roots of Mn stressed plants with 100 μM Fe were reduced significantly although still above critical toxicity levels, indicating that elevation of Fe could ameliorate Mn toxicity to some extent.

Phytosiderophore release from manganese-induced iron deficiency in barley.

Abstract An experiment was conducted in the phytotron with barley (Hordeum vulgare L. cv. Minorimugi) grown in nutrient solution to compare iron (Fe) deficiency caused by the lack of Fe with manganese (Mn)‐induced Fe deficiency. Dark brown spots on older leaves and stems, and interveinal chlorosis on younger leaves were common symptoms of plants grown in either Mn‐toxic or Fe‐deficient treatments. Dry matter yield was affected similarly by Fe deficiency and Mn toxicity. The Mn toxicity significantly decreased the translocation of Fe from roots to shoots, caused root browning, and inhibited Fe absorption. The rate of Fe translocated from roots to shoots in the 25.0 μM Mn (toxic) treatment was similar to the Fe‐deficient treatment. Manganese toxicity, based on the release of phytosiderophore (PS) from roots, decreased from 25.0>250>2.50 uM Mn. The highest release of PS from roots occurred 7 and 14 days after transplanting (DAT) to Mn‐toxic and Fe‐deficient treatments, respectively; but was always higher in the Fe‐deficient treatment than the Mn‐toxic treatments. The release of PS from roots decreased gradually with plant age and with severity of the Mn toxicity symptoms. The PS content in roots followed the PS release pattern.

Concentrations of iron and phytosiderophores in xylem sap of iron-deficient barley plants

Abstract Barley (Hordeum vulgare L. cv. Minorimugi) plants were grown hydroponically in a greenhouse under natural sunlight. The xylem sap was collected from the barley plants showing iron (Fe) deficiency symptoms in order to determine the concentrations of the mugineic acid family of phytosiderophores (PS) and Fe. The compounds of PS in the xylem sap were identified, using TLC and HPLC, as mugineic acid (MA) and 2′-deoxymugineic acid (DMA). Feeding experiments were conducted to study the effects of PS on the concentrations of Fe and PS in the xylem sap of barley plants grown under Fe-deficient conditions. The concentration of Fe in the xylem sap of the Fe-deficient plants supplied with Fe3+ (30 αM) together with varying concentrations of PS (0 to 30 αM) increased with the increase in the PS concentration in the nutrient solution, indicating the specific role of PS in the acquisition of Fe3+ by the roots. On the other hand, PS concentration in the xylem sap increased at the highest external PS concentration (30 αM). The PS : Fe ratio in the xylem sap decreased with the increase in the concentration of PS supplied to the roots. The effects of the addition of 30 αM Fe3+ and equimolar concentration of PS or ethylene diamine tetraacetic acid (EDTA) to the Fe-deficient plants were compared. Plants supplied with PS showed a higher Fe concentration in the xylem sap than those which received EDTA, suggesting that PS were more effective than EDTA in the absorption and translocation of Fe3+.

Alleviation of Manganese Phytotoxicity in Barley with Calcium

ABSTRACT In order to clarify the mechanism by which calcium (Ca) alleviates manganese (Mn) phytotoxicity, barley plants were grown under the following conditions: (1) nutrient solution alone (control), (2) nutrient solution + 25 μM Mn (Mn-toxic), and (3) nutrient solution + 25 μ M Mn + 20 mM Ca (Ca-alleviated). Feeding experiments using 54Mn and 59Fe (iron) with 2.0 or 20 mM Ca to the plant roots were also conducted. The absorption and translocation of 54Mn in the control plants were lowered by the high-Ca (20 mM) feeding condition. The translocation of 54Mn to shoots of Mn-toxic or Ca-alleviated plants was also lowered by the high-Ca feeding condition, but 54Mn absorption by roots of the plants was unaffected. The absorption and translocation of 59Fe in the plants was unaffected by the high-Ca feeding condition. Calcium alleviation of Mn phytotoxicity in barley may be induced mainly by the inhibition of Mn translocation to shoots.

Effect of Iron Deficiency on the Chemical Composition of the Xylem Sap of Barley

Abstract Barley (Hordeum vulgare L.) plants were grown hydroponically, and the effect of Fe deficiency on the concentration of essential metals, phytosiderophores (PS), organic acids, and amino acids, in the xylem sap was elucidated. The Fe-deficient plants exuded xylem sap at a rate about 2A-fold lower than the Fe-sufficient plants. Under Fe deficiency, the concentration of Fe decreased compared with that of Fe-sufficient plants, while the concentrations of K, Ca, and Mg were not significantly different, and those of Mn, Zn, and Cu increased by Fe deficiency. The concentration of PS in the xylem sap of the Fe-deficient plants was about 24-fold higher than that of the Fe-sufficient plants. The concentrations of citrate, malate, and succinate in the xylem sap increased 7.3-fold, 2.0-fold, and 1.8-fold, respectively, with Fe deficiency compared to those of the Fe-sufficient plants. The xylem concentration of total amino acids increased 1.4-fold by Fe deficiency.

Effect of low phosphorus and iron-deficient conditions on phytosiderophore release and mineral nutrition in barley

Abstract To investigate the effect of low phosphorus (P) conditions on phytosiderophore (PS) release and mineral nutrient status in graminaceous plants, an experiment was conducted in a phytotron with barley plants grown in iron-deficient (Fe0) nutrient solutions with four P levels (0.5, 5, 50, 500 [control]µmol L−1) at pH 6.5 for 21 days after treatment (DAT). The results showed that the growth and chlorophyll index of plants cultured under low P conditions (0.5, 5 and 50 µmol L−1) were higher than those of the control plants. The accumulation amount (mg or µg/plant) of mineral nutrients in shoots was higher for potassium, iron and copper in plants in the low P treatment than in the control plants. The accumulation of PS in roots and the amount of PS released from the roots at 14 DAT were lower in plants in the Fe0 and low P treatments. These results indicated that low P depressed PS release from roots and PS accumulation in roots in Fe0 barley. This might result from the higher Fe content in shoots and the alleviation of Fe chlorosis with low P treatment of plants. These results showed that low P treatment enhanced the growth, chlorophyll index and Fe mobilization to shoots in Fe0 barley. Low P conditions alleviated Fe-deficiency symptoms, suggesting that P is physiologically competing with Fe in plant tissues.

Metal micronutrients in xylem sap of iron-deficient barley as affected by plant-borne, microbial, and synthetic metal chelators

Abstract A greenhouse experiment was conducted to study the effects of phytosiderophore (PS), deferriferrioxamine B (Desferal), and ethylene diamine tetraacetic acid (EDTA) on the concentrations of copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) in the xylem sap of Fe-deficient barley (Hordeum vulgare L. cv. Minorimugi) plants grown in 1/2-strength modified Hoagland-Arnon nutrientsolution. Iron-deficient plants (14 d after transfer) were treated with 25, µM metal chelators for 3 h after which the xylem sap was collected for 3 h. Treated plants were compared with Fe-sufficient and untreated Fe-deficient plants. The concentration and translocation of PS, Mn, and Zn increased, while those of Fe decreased in xylem sap of the Fe-deficient plants compared to the Fe-sufficient plants. The concentrations of PS, Cu, Fe, Mn, and Zn in the xylem sap of the Fe-deficient plants increased by the application of PS to the nutrient solution. This fact suggested that PS solubilized the metal micronutrients in the root tissues and/or root apoplast and contributed to the loading of the nutrients to the xylem tubes, thereby leading to a higher nutrient absorption from the rhizosphere of Fe-deficient plants. On the other hand, Fe-deficient plants treated with EDTA showed a decrease in the PS, Cu, Fe, Mn, and Zn concentrations in the xylem sap. Application of Desferal to the nutrient solution slightly increased only the Fe concentration in the xylem sap of the Fe-deficient plants. Organic acids in the xylem sap of the Fe-deficient plants were in the order of succinate > malate > citrate based on the concentrations, and did not appear to be related to the translocation of metal micronutrients.

Amelioration of Manganese Toxicity in Young Rice Seedlings with Potassium

Abstract A hydroponic experiment was conducted in a controlled‐temperature glasshouse for 14 days to study the effect of additional potassium (K) on the amelioration of manganese (Mn) toxicity in young rice (Oryza sativa L. cv. Kakehashi) seedlings. Reduced growth, rolling of old leaves, brown spots and interveinal chlorosis on young leaves, and root browning were the main symptoms of Mn toxicity in plants grown with high Mn (1.0 mM) and adequate K (1.0 mM). Application of additional K (10 mM) to the nutrient solution increased chlorophyll concentration and dry matter yields of plants grown in high Mn, but did not restore dry matter accumulation to the level achieved in the control plants. Plants grown in 1.0 mM Mn and 10 mM K had lower tissue Mn concentration on a dry matter basis than plants grown in 1.0 mM Mn and 1.0 mM K and did not show leaf injury symptoms, but still showed root browning; however, the accumulation (per plant basis) of Mn was approximately the same, indicating that additional K increased the tolerance of the plant to high Mn. The concentration and accumulation of iron (Fe) in shoots of plants grown at 1.0 mM K with 1.0 mM Mn was lower than in the control plants, indicating an inhibition of Fe translocation to shoots by high Mn. Additional K increased both concentration and accumulation of Fe in shoots and roots of plants grown in high Mn. The higher phosphorus (P), K, zinc (Zn), and copper (Cu) concentrations in shoots and roots of plants grown in 1.0 mM Mn and 1.0 mM K could be a concentration effect because of severe growth reduction, while lower calcium (Ca) and magnesium (Mg) concentrations were probably due to competition with Mn at the absorption sites. Additional K further decreased Ca and Mg concentrations, indicating possible interference of K with the absorption and physiological availability of Ca and Mg. Additional K increased K concentrations and decreased P, Cu, and Zn concentrations in shoots and roots of plants grown with high Mn. These results suggest that additional K can partially alleviate the symptoms of Mn toxicity and Mn‐induced Fe deficiency in rice seedlings and significantly improve plant growth.

Mechanism of Potassium Alleviation of Manganese Phytotoxicity in Barley

ABSTRACT Manganese (Mn) toxicity and potassium (K) deficiency are the major factors that limit plant growth and development in acid soils. The objective of this study was to assess the role of high K on the alleviation of Mn toxicity in barley (Hordeum vulgare L. cv. ‘Minorimugi’) grown in a phytotron for 14 d. Modified half-strength Hoagland-Arnon solution (pH 5.5) was used as the medium. The treatments were (1) 0.25 μ M Mn + 3 mM K (control); (2) 25 μ M Mn + 3 mM K (Mn-toxic); and (3) 25 μ M Mn + 30 mM K (K-alleviated). The Mn-toxic plants showed the symptoms of Mn toxicity and mild iron (Fe) deficiency, whereas in the K-alleviated plants such symptoms were absent. The K-alleviated plants had dry weight, chlorophyll content, and Fe concentration similar to that in the control plants, indicating that high K (30 mM) in the growth medium could alleviate Mn toxicity and Mn-induced Fe deficiency. Roots of plants fed separately with 54Mn and 59Fe in the presence of 3.0 and 30 mM K for 4 h were also studied. Results showed that high K could help in avoiding the accumulation of 54Mn, indicating that K plays an antagonistic role on Mn absorption by roots of barley and its subsequent translocation to the shoots. However, the absorption of 59Fe was not influenced by the high K concentration in a short-term experiment (4 h), indicating that high K does not affect short-term Fe absorption by the roots of barley plants. These results suggested that the alleviating effect of high K could be attributed to the antagonistic effect of K on Mn absorption by roots and translocation into shoots.

RESPONSE OF IRON-DEFICIENT BARLEY PLANTS TO MANGANESE IN NUTRIENT SOLUTION

Barley (Hordeum vulgare L. cv. Minorimugi) plants were cultured in iron (Fe)-deficient nutrient solutions at three levels (0.25, 0.025, and 0.0025 μM) of manganese (Mn). Iron-deficient plants with high Mn (0.25 μM) had brown spots on older leaves and stems characteristic of Mn toxicity. In the nutrient solution at 0.0025 μM Mn, the younger leaves had typical symptoms of Mn deficiency. Iron-deficient plants with 0.025 μM Mn had shoot Mn concentration statistically similar to Fe-sufficient plants with 0.25 μM Mn. Tissue Fe and Mn concentrations were reciprocally related in shoots and roots of plants grown in 0.25 μM Mn with and without Fe. The Mn concentration of Fe-deficient plants decreased with decreasing Mn concentrations in the nutrient solution. In contrast, the Mn levels in the nutrient solution did not significantly affect the Fe concentrations of Fe-deficient plants with identical Fe deficiency symptoms. The highest level of phytosiderophore (PS) released from roots of Fe-deficient plants occurred with 0.025 μM Mn and the least with 0.0025 μM Mn. A deficiency of Fe decreased the translocation of Fe and Cu from roots to shoots, but had little or no effect on the translocation of Mn and Zn.