Involvement of Antioxidative Defense System in Rice Seedlings Exposed to Aluminum Toxicity and Phosphorus Deficiency

Plants growing in acid soils may suffer both phosphorus （P） deficiency and aluminum （Al） toxicity.Hydroponic experiments were undertaken to assess the single and combination effects of Al toxicity and low P stress on seedling growth,chlorophyll and proline contents,antioxidative response and lipid peroxidation of two rice genotypes （Yongyou 8 and Xiushui 132） differing in Al tolerance.Al toxicity and P deficiency both inhibited rice seedling growth.The development of toxic symptoms was characterized by reduced chlorophyll content,increased proline and malondialdehyde contents in both roots and leaves,and increased peroxidase and superoxide dismutase activities in roots,but decreased in leaves.The stress condition induced more severe growth inhibition and oxidative stress in Yongyou 8,and Xiushui 132 showed higher tolerance to both Al toxicity and P deficiency.P deficiency aggravated Al toxicity to plant growth and induced more severe lipid peroxidation.

Performance of tetraploid alfalfa genotypes as exposed to aluminum toxicity

A study was carried out to evaluate the development of 12 tetraploid alfalfa cultivars exposed to Al toxicity in nutrient solution. Newly germinated seedlings of cultivars Alfa 200, Alto, Araucana, Costera, Crioula, Esmeralda, Falcon, F-708, Rio, Romagnola, Valley Plus, and Victoria, were exposed to either 0, 4, 8 or 12 mg·L-1 Al3+. Plants were analyzed regarding root length (RL) and dry matter (RDM), aerial part length (APL), and dry matter (APDM), hypocotyl length (HypL) and dry matter (HypDM), epicotyl length (EpiL) and dry matter (EpiDM), and petiole length (PetL), and dry matter (PetDM). Results indicated that, although all genotypes exhibited detectable sensitivity to such a stress, cvs. Crioula, Victoria and Alpha-200 were tolerant to 4 mg·L-1 Al3+ toxicity. It was also concluded that Al3+ levels up to the 4 mg·L-1 will be effective for screening tetraploid alfalfa genotypes regarding this type of stress, when evaluations are made in nutrient solution. Finally, RL is the most suitable variable for conducting such evaluations, but all variables related to dry matter in the aerial part are also recommended.

Physiological and Proteomic Analyses Reveal Effects of Putrescine-Alleviated Aluminum Toxicity in Rice Roots

The effects of putrescine on improving rice growth under aluminum(Al)toxicity conditions have been previously demonstrated,however,the underlying mechanism remains unclear.In this study,treatment with 50 pmol/L Al significantly decreased rice root growth and whole rice dry weight,inhibited Ca2+uptake,decreased ATP syn thesis,and in creased Al,H2O2 and malon dialdehyde(MDA)con tents,whereas the application of putrescine mitigated these negative effects.Putrescine increased root growth and total dry weight of rice,reduced total Al content,decreased H2O2 and MDA contents by increasing antioxidant enzyme(superoxide dismutase,peroxidase,catalase and glutathione S・transferase)activities,increased Ca2+uptake and energy product!oru Proteomic analyses using data-independent acquisition successfully identified 7934 proteins,and 59 representative proteins exhibiting fold-change values higher than 1.5 were randomly selected.From the results of the proteomic and biochemical analyses,we found that putrescine significantly inhibited ethylene biosynthesis and phosphorus uptake in rice roots,increased pectin methylation,decreased pectin content and apoplastic Al deposit!on in rice roots.Putrescine also alleviated Al toxicity by repairing damaged DNA and increasing the proteins involved in maintaining plasma membra ne integrity and normal cell proliferation.These fin dings improve our understanding of how putrescine affects the rice response to Al toxicity,which will facilitate further studies on environmental protection,crop safety,in novations in rice performance and real-world producti on.

Alleviation of Al Toxicity in Barley by Addition of Calcium

The potential mechanism by which Ca alleviates Al toxicity was investigated in barley seedlings. It was found that 100 Al-alone treatment inhibited barley plant growth and thereby reduced shoot height and root length, and dry weights of root, shoot and leaf; promoted Al accumulation but inhibited Ca absorption in plant tissues; and induced an increase in the activities of superoxide dismutase （SOD）, catalase （CAT）, and peroxidase （POD） and in the level of lipid peroxidation （MDA content） in leaves. Except for the increase in Ca concentration in plant tissues, treatment with 0.5 mM Ca in the absence of Al had less effect on the above-mentioned parameters, compared with the control. Addition of Ca efficiently reduced Al toxicity, which is reflected by the promotion of plant growth, reduction in Al concentration and MDA content, increase in Ca concentration and in SOD, POD, and CAT activities compared with the Al-alone-treatment; with increase in Ca level （3.0 raM）, the ameliorative effect became more dominant. This indicated that the alleviation of aluminum toxicity in barley seedlings with Ca supplementation could be associated with less absorption of Al and the enhancement of the protective ability of the cell because of increased activity of the antioxidative enzyme.

Genotypic Difference in Plant Growth and Mineral Composition in Barley Under Aluminum Stress

Four barley genotypes (Tiantaiyangdamai, Xiyin2, Mimaill4 and Tai94-Ce6) were exposed to 0, 50, 100, and 150μM of Al-containing solution with pH 4.5, to determine the differences in growth inhibition , Al concentration and accumulation and mineral composition among genotypes. The results showed that Mimaill4 and Tai94-Ce6 had significantly higher Al concentration and accumulation than Tiantaiyangdami and Xiyin2, especially in roots, and the growth traits including root and shoot dry weights, shoot height, root length and tillers per plant were more inhibited in the former two genotypes. Al treatments caused a significant reduction of N, P, K, Ca, Mg and Mn content in both roots and shoots, of Cu in shoots; and a significant increase in Fe and Zn content in both roots and shoots, of Cu in roots. The changed rates of mineral content caused by Al treatments, in terms of the content in 150μM Al divided by the content in the control, differed significantly among four genotypes. Two Al-sensitive genotypes, Mimaill4 and Tai94-Ce6 had much greater changes in mineral content than other two Al-tolerant genotypes Tiantaiyangdamai and Xiyin2 when subjected to Al stress in comparison with the control. It is indicated that the Al-tolerant genotype is characterized by less uptake and accumulation of Al in roots and smaller disorders in mineral metabolism and ion homeostasis.

Genetic improvement of legume roots for adaption to acid soils

Acid soils occupy approximately 50% of potentially arable lands.Improving crop productivity in acid soils,therefore,will be crucial for ensuring food security and agricultural sustainability.High soil acidity often coexists with phosphorus(P) deficiency and aluminum(Al) toxicity,a combination that severely impedes crop growth and yield across wide areas.As roots explore soil for the nutrients and water required for plant growth and development,they also sense and respond to below-ground stresses.Within the terrestrial context of widespread P deficiency and Al toxicity pressures,plants,particularly roots,have evolved a variety of mechanisms for adapting to these stresses.As legumes,soybean(Glycine max) plants may acquire nitrogen(N) through symbiotic nitrogen fixation(SNF),an adaptation that can be useful for mitigating excessive N fertilizer use,either directly as leguminous crop participants in rotation and intercropping systems,or secondarily as green manure cover crops.In this review,we investigate legumes,especially soybean,for recent advances in our understanding of root-based mechanisms linked with root architecture modification,exudation and symbiosis,together with associated genetic and molecular strategies in adaptation to individual and/or interacting P and Al conditions in acid soils.We propose that breeding legume cultivars with superior nutrient efficiency and/or Al tolerance traits through genetic selection might become a potentially powerful strategy for producing crop varieties capable of maintaining or improving yields in more stressful soil conditions subjected to increasingly challenging environmental conditions.

Protecting Cell Walls from Binding Aluminum by Organic Acids Contributes to Aluminum Resistance

Aluminum-induced secretion of organic acids from the root apex has been demonstrated to be one major AI resistance mechanism in plants. However, whether the organic acid concentration is high enough to detoxify AI in the growth medium is frequently questioned. The genotypes of AI-resistant wheat, Cassia tora L. and buckwheat secrete malate, citrate and oxalate, respectively. In the present study we found that at a 35% inhibition of root elongation, the AI activities in the solution were 10, 20, and 50 μM with the corresponding malate, citrate, and oxalate exudation at the rates of 15, 20 and 21 nmol/cm2 per 12 h, respectively, for the above three plant species. When exogenous organic acids were added to ameliorate AI toxicity, twofold and eightfold higher oxalate and malate concentrations were required to produce the equal effect by citrate. After the root apical cell walls were isolated and preincubated in 1 mM malate, oxalate or citrate solution overnight, the total amount of AI adsorbed to the cell walls all decreased significantly to a similar level, implying that these organic acids own an equal ability to protect the cell walls from binding AI. These findings suggest that protection of cell walls from binding AI by organic acids may contribute significantly to AI resistance.

Aluminum-activated Oxalate Secretion does not Associate with Internal Content among Some Oxalate Accumulators

Although aluminum （AI）-activated secretion of oxalate has been considered to be an important AI-exclusion mechanism, whether it is a general response in oxalate accumulators and related to oxalate content in roots are still not clear. Here, we examined the oxalate secretion and oxalate content in some oxalate accumulators, and investigated the role of oxalate secretion in AI resistance. When oxalate content in amaranth roots was decreased by about 50% with the increased ratio of NH4^＋-N to NO3^- -N in nutrient solution, the amount of AI-activated oxalate secretion still remained constant. There was no relationship between the content of the water soluble oxalate in four species of oxalate accumulators and the amount of the AI-activated oxalate secretion in roots. Furthermore, oxalate secretion is poorly associated with AI resistance among these species. Based on the above results, we concluded that although all of the oxalate accumulators tested could secrete oxalate rapidly, the density of anion channels in plasma membrane may play a more important role in AI-activated oxalate secretion.

Molecular mechanisms of plant adaptation to acid soils: A review

Acid soils are widespread and limit global plant production.Aluminum(Al)/manganese(Mn)toxicity and phosphorus(P)deficiency are the major limiting factors affecting plant growth and productivity on acid soils.Plants,however,have evolved various strategies to adapt to these stresses.These strategies include using both external and internal mechanisms to adapt to Al toxicity,regulating Mn uptake,translocation,and distribution to avoid Mn toxicity,and orchestrating a set of P transport mechanisms to efficiently take up P from the soil.Here,we review the current state of knowledge about the molecular mechanisms of plant adaptation to these constraints in acid soils,focusing on the roles of transporters involved in Al/Mn tolerance and P efficiency.Gene manipulation combined with other biotechnology will contribute to the development of novel strategies to improve plant adaptation to acid soils.The molecular mechanisms of plant coadaptation to multiple stresses in acid soils are largely unknown and require further investigation.

Management of Aluminium Phosphide Poisoning with a Holistic Approach at NHL Municipal Medical College and Hospital,Ahmedabad

Background:Aluminium phosphide is a usual ingredient of rodenticide and its poisoning is a common cause of suicide in India.Signs and symptoms of its toxicity are well-known.Its toxic effects are mainly due to liberation of phosphine gas which causes cell hypoxia due to inhibition of oxidative phosphorylation and results in circulatory failure.Aims and Objectives:Mortality with aluminium phosphide is high as there is no specific antidote available yet.And hence we need to explore holistic treatment approach to improve patient outcomes in aluminium phosphide poisoning.Materials and Methods:Present study discusses a holistic treatment approach to aluminium phosphide poisoning in this retrospective analysis of 100 cases from a tertiary care hospital in this study.Results:Around 65%patients survived due to the holistic treatment approach and correct treatment protocol with supportive therapy.Conclusions:The aggressive and appropriate management with continuous hemodynamic monitoring and holistic treatment approach can reduce the mortality significantly in aluminium phosphide poisoning.