A. K. M. Zakir Hossain

Aluminum-Induced Lipid Peroxidation and Lignin Deposition Are Associated with an Increase in H2O2 Generation in Wheat Seedlings

Wheat (Triticum aestivum cv. Kalyansona) seedlings were exposed to 0, 10, 50, and 100 μM Al in a 250 μM CaCl2 solution for 24 h at pH 4.5. Root elongation decreased gradually, while the Al content markedly increased with increasing supply of Al in the solution. The generation of H2O2 during Al stress was investigated biochemically and histochemically, as well as other events related to the decomposition of H2O2. After 24 h treatment, root elongation inhibition was detected at all the concentrations of Al. The level of lipid peroxidation at 10 μM Al after 24 h treatment was similar to that of the control, while a significant increase in lipid peroxidation was detected at 50 and 100 μM Al. H2O2 generation was higher at 50 and 100 μM Al than that at 10 μM Al. These results suggest that Al-inducible lipid peroxidation may require excessive yield of H2O2. Time course experiment with 10 μM Al indicated that there is a strongly positive correlation between root elongation inhibition and cellular H2O2 yield. There were no significant changes in the activities of catalase (CAT) and ascorbate peroxidase (APX) in roots at 10 μM Al after 24 h treatment. However, a significant decrease in the activities of CAT and APX and a large increase in the activities of oxalate oxidase (OXO), guaiacol peroxidase (GPX), and coniferyl alcohol peroxidase (CA-POX) as well as lignin deposition were observed at 100 μM Al. These results suggest the possible involvement of OXO in the production of a large amount of H2O2 under severe Al stress, whereas GPX and CA-POX may be involved in the degradation of H2O2, leading to lignin deposition.

Effects of aluminum and boron supply on growth of seedlings among 15 cultivars of wheat (triticum aestivum L.) grown in Bangladesh

Abstract Aluminum toxicity and boron deficiency are the major factors that limit plant growth and development in acid soils and in B-deficient soils. Root growth inhibition is an early symptom of AI toxicity and B deficiency. Effects of AI and B supply and their interaction on the growth of wheat (Triticum aestivum L.) seedlings were investigated using hydroponics. Fifteen wheat cultivars commonly grown in Bangladesh were used and found to differ considerably in their tolerance to AI toxicity and B deficiency. The relative root length of all the wheat cultivars at 50 µM AI (pH 4.5) ranged from 27 to 71% relative to the control (0 µM AI). Among the cultivars, Inia66 and Kalyansona were found to be the most Al-tolerant and sensitive cultivars, respectively, based on the data of relative root length, malate exudation and AI content of roots. Malate was detected in all the cultivars in the presence of 100 µM AI (pH 4.3). Inia66 exuded a 6-fold larger amount of malate and the AI content of roots was 4 times lower than that in Kalyansona. The vigorous seedling growth was observed at 40 µM B among the series of B treatments. Considerable cultivar differences in response to 40 µM B were observed among the 15 cultivars. Kalyansona was considered to be the most sensitive and Kheri the most tolerant to B deficiency. The interaction effects of B ( 40 and 200 µM) and AI (50 µM) on seedling growth were also examined in Inia66 and Kalyansona. Root growth was inhibited in the presence of Al but B supply especially at 200 µM B in the Kalyansona cultivar caused a slight improvement.

Combined effects of Mg and Ca supply on alleviation of Al toxicity in wheat plants

Abstract A Bangladeshi wheat (Triticum aestivum) cultivar, Kalyansona, was exposed to 100 J.µ Al with varying concentrations of Ca (250, 500, 2,500 J.µM) and Mg (103, 1,029, 4,115 J.µ) in the nutrient solution for 14 d. Exposure to Al along with low concentrations of both Ca and Mg caused severe damage to the root apex. Under AI-stressed conditions, an increased supply of Mg from 103 to 1,029 J.µ enhanced the root length by 44, 22, and 3% at 250, 500, and 2,500 J.µ Ca, respectively. Root growth at 2,500 J.µ Ca was not affected by additional Mg concentration. Again, an increased supply of Mg from 103 to 4,115 J.µ enhanced the root length by 56% at 500 J.µ Ca. Under the Al-stressed conditions, the increase in the root length was correlated with the decrease in the Al content in roots. Our results suggest that Mg alleviates Al toxicity efficiently in the presence of Ca at a low level in the culture solution by decreasing Al accumulation in roots.

Role of Accumulated Calcium in Alleviating Aluminum Injury in Wheat Plants

Aluminum (Al) sensitive wheat cultivar kalyansona was grown for 14 d in a range of Ca solution (125, 625, and 2500 μM) plus other nutrients without Al. At 14 d after Ca treatment, half of these plants were harvested (H1), and the rest of the plants were exposed to 100 μM Al for additional 6 d and harvested (H2). Severe Al injury was found only in the plants with the lowest supply of Ca before Al treatment. Aluminum concentration in the apoplastic fluid was very high at 125 μM Ca probably because the plasma membrane of some of the cells was destroyed due to the attack of 100 μM Al. Aluminum content in roots decreased with increasing supply of Ca before Al treatment. Calcium content decreased drastically at harvest (H2) in the plants with 100 μM Al. Under Al stress conditions, the plant responded to Al in different ways due to not only the different Ca supply but also the variation of Ca content in the plant tissues. Actually, the plants having the largest Ca content in the roots before Al treatment can receive less Al injury during Al treatment. To substantiate this idea, a companion study was conducted to investigate the effects of 2500 μM Ca supply during, before, and after 100 μM Al treatment on root growth. The results indicated clearly that exogenous Ca supply before Al treatment is able to alleviate Al injury but less effective than Ca supply during Al treatment.

Boron-Calcium Synergically Alleviates Aluminum Toxicity in Wheat Plants (Triticum aestivum L.)

The effects of B and Ca treatments on root growth, nutrient localization and cell wall properties in wheat (Triticum aestivum L.) plants with and without Al stress were investigated. Seedlings were grown hydroponically in a complete nutrient solution for 7 d and then treated with B (0, 40 μM), Ca (0, 2,500 μM), and Al (0, 100 μM) in a 500 μM CaCl2 solution for 8 d. The cell wall materials (CWM) were extracted with a phenol: acetic acid: water (2:1:1 w/v/v) solution and used for subsequent pectin extraction with trans-1,2-diami-nocyclohexane-N,N,N,N-tetraacetic acid (CDTA) and Na2CO3 solutions. Boron, Ca, and B + Ca treatments enhanced root growth by 19.5, 15.2, and 27.2%, respectively, compared to the control (pH 4.5). Calcium and B+Ca treatments enhanced root growth with Al stress by 43 and 54%, respectively, while B did not exert any effect. The amounts of CWM and pectin per unit of root fresh weight increased by Al treatment, whereas the Ca and B+Ca treatments slightly reduced the contents of these components. Seventy-four percent of total B, 69% of total Ca, and 85% of total Al were located in the cell wall in the B, Ca, and Al treatments, respectively and 32% of total B, 33% of total Ca, and 33% of total Al were located in the CDTA-soluble and Na2CO3-soluble pectin fractions. A more conspicuous localization of B was observed in the presence of Al. Aluminum treatment markedly decreased the Ca content in the cell wall as well as pectin fractions, mainly in the case of the CDTA-soluble pectin fraction. Boron + Ca treatment decreased the Al content in the cell wall and pectin fractions compared to the Ca treatment alone in the presence of Al. It is concluded that the B+Ca treatment enhanced root growth and, B and Ca uptake, and helped to maintain a normal B and Ca metabolism in the cell walls even in the presence of Al.