Evaluation of aluminium tolerance in grapevine rootstocks

Electronic Journal of Biotechnology, 2010

Plant and Soil, 2004

Shooting stage roots of cereal plants varying in Al tolerance: rye (Secale L.), triticale (Triticale), barley (Hordeum L.) and four wheat (Triticum L.) varieties grown at pH 7 (controls) and stressed during 10 days at pH 4 with aluminium concentrations ranging from 0 to 40 mg dm −3 were back titrated with NaOH. Back-titration data were used for estimation of variable surface charge vs. pH dependencies and apparent surface dissociation constants distribution functions. Roots grown at pH 4 without Al addition had apparently the same charge properties as the control roots. With the increase of the concentration of the aluminium treatment, the variable surface charge of the roots decreased, beginning at 5 mg Al dm −3 for barley, at 10 mg Al dm −3 for wheat and triticale (20 mg Al dm −3 for acid resistant wheat Inia), and at 40 mg Al dm −3 for rye, and a weakening of root surface acidity was deduced from the decrease in average surface dissociation constant of the root surface. The latter was connected with an increase of the relative number of weakly acidic surface sites and a simultaneous decrease in surface groups of medium and strong acidity. During Al stress the density of variable surface charge of the roots decreased markedly. Changes in surface charge properties of Al-tolerant species were less intensive than for Al-sensitive ones.

Stress Responses in Plants, 2015

Achieving sustainable food production to feed the increasing population of the problematic lands of the world is an enormous challenge. Aluminum (Al) toxicity in the acid soil is a major worldwide problem. Liming and nutrient management technologies are worthless due to high lime requirement, and the effect of liming does not persist for long. Besides this, conventional breeding is useful to manage Al toxicity as some plants have evolved mechanisms to cope with Al toxicity in acid soil. Therefore, understanding of Al tolerance mechanisms is prime necessity for improving Al tolerance in crops. Al resistance mechanisms include mainly Al avoidance (Al exclusion) and/or Al tolerance (detoxification of Al inside the cell) mechanisms. In this chapter, we summarize Al behavior in plant root cell. We include recent findings of Al resistance mechanisms and Al-resistant genes which can be useful to produce cultivars adapted to acid soils.

Environmental and Experimental Botany, 2005

The common sorrel, Rumex acetosa L. is well adapted to acid mineral soils with high availability of phytotoxic Al species. The mechanisms of Al resistance in this species are not established. Our goal was to assess the possible implications of organic acids and phenolic substances in Al detoxification in roots and shoots of this plant. R. acetosa plants were exposed in nutrient solution (pH 4.3) to a non-growth reducing Al concentration of 50 M Al for 5 days. Exclusion of Al from root tips was visualized by haematoxylin staining. Tissue Al and Ca concentrations were analysed by ICP ES. Root and shoot concentrations of organic acids and phenolic substances were analysed by HPLC. A time-dependent (model II type) Al exclusion pattern in root tips was observed. Nonetheless, high Al concentrations accumulated in roots (1170 g/g) and shoots (275 g/g). Aluminium supply enhanced root citrate concentrations but decreased shoot organic acid levels. Aluminium induced high levels of anthraquinone in roots and of catechol, catechin and rutin in shoots. Aluminium resistance in R. acetosa implies both exclusion of Al from root tips and tolerance to high Al tissue concentrations. Citrate in roots and phenolics in shoots may bind Al in non-toxic form. Anthraquinones, as strong antioxidants, may play a role in a general defence response to the root stress.

Plant and Soil, 2005

Aluminum (Al) toxicity is the primary factor limiting crop production on acidic soils (pH values of 5 or below), and because 50% of the world’s potentially arable lands are acidic, Al toxicity is a very important limitation to worldwide crop production. This review examines our current understanding of mechanisms of Al toxicity, as well as the physiological, genetic and molecular basis for Al resistance. Al resistance can be achieved by mechanisms that facilitate Al exclusion from the root apex (Al exclusion) and/or by mechanisms that confer the ability of plants to tolerate Al in the plant symplasm (Al tolerance). Compelling evidence has been presented in the literature for a resistance mechanism based on exclusion of Al due to Al-activated carboxylate release from the growing root tip. More recently, researchers have provided support for an additional Al-resistance mechanism involving internal detoxification of Al with carboxylate ligands (deprotonated organic acids) and the sequestration of the Al-carboxylate complexes in the vacuole. This is a field that is entering a phase of new discovery, as researchers are on the verge of identifying some of the genes that contribute to Al resistance in plants. The identification and characterization of Al resistance genes will not only greatly advance our understanding of Al-resistance mechanisms, but more importantly, will be the source of new molecular resources that researchers will use to develop improved crops better suited for cultivation on acid soils.

Abiotic Stress in Plants - Mechanisms and Adaptations, 2011

Acid soils limit crop yields around the world due to nutrient deficiencies and mineral toxicities. Non-adapted plants grown on acid soils typically have smaller root systems because high concentrations of soluble aluminium (Al 3+ ) inhibit root elongation. This restricts their ability to acquire water and nutrients. Plants vary widely in their capacity to tolerate acid soils and even genotypes within species show significant variation. The physiology and genetics controlling this variability have been studied for many years. The analysis of segregating populations and mutants has helped identify the mechanisms and genes controlling aluminium resistance in many species including wheat, rice, Arabidopsis, barley and sorghum. The release of organic anions from roots is an important mechanism of resistance in a wide variety of species. This trait is controlled by genes from two distinct gene families that encode transport proteins. Sufficient information is now available for enhancing the aluminium resistance of important crop species using biotechnology. We will review progress in understanding the mechanisms of Al 3+ resistance in plants, the genes controlling these mechanisms and the application of genetic engineering to increase the Al 3+ resistance of important crop plants. This approach can help maintain and even increase food production on acid soils in the future. Soil pH is an important consideration for agriculture production . Some plants are sensitive to high or low pH, nutrient availability and mineral toxicities are influenced by pH and soil microbial communities are significantly affected by pH . Acid soils present multiple stresses to plants including proton toxicity, nutrient deficiencies (especially calcium, magnesium and phosphorus) and metal-ion toxicities especially aluminium and manganese. The United States Department of Agriculture classifies acid soils into five levels: ultra acid soils (below pH 3.5), extremely acid (pH 3.5 to 4.4), very strongly acid (pH 4.5 to 5.0), strongly acid (pH 5.1 to 5.5), moderately acid (pH 5.6 to 6.0) and slightly acid (pH 6.1 to 6.5). Soils with pH≤5.5 can adversely affect the production of many major food crops.

Plant Cell, Tissue and Organ Culture, 2003

Development of acid soils that limit crop production is an increasing problem worldwide. Many factors contribute to phytotoxicity of these soils, however, in acid soils with a high mineral content, aluminum (Al) is the major cause of toxicity. The target of Al toxicity is the root tip, in which Al exposure causes inhibition of cell elongation and cell division, leading to root stunting accompanied by reduced water and nutrient uptake. Natural variation for Al tolerance has been identified in many crop species and in some crops tolerance to Al has been introduced into productive, well-adapted varieties. Aluminum tolerance appears to be a complex multigenic trait. Selection methodology remains a limiting factor in variety development as all methods have particular drawbacks. Molecular markers have been associated with Al tolerance genes or quantitative trait loci in Arabidopsis and in several crops, which should facilitate development of additional tolerant varieties. A variety of genes have been identified that are induced or repressed upon Al exposure. Most induced genes characterized so far are not specific to Al exposure but are also induced by other stress conditions. Ectopic over-expression of some of these genes has resulted in enhanced Al tolerance. Additionally, expression of genes involved in organic acid synthesis has resulted in enhanced production of organic acids and an associated increase in Al tolerance. This review summarizes the three main approaches that have been taken to develop crops with Al tolerance: recurrent selection and breeding, development of Al tolerant somaclonal variants and ectopic expression of transgenes to reduce Al uptake or limit damage to cells by Al.

2013

Aluminium (Al) is the most abundant metal in the earth's crust, comprising about 7% of its mass. A large amount of Al is incorporated into aluminosilicate soil minerals and very small quantities appear in the soluble form. Aluminium toxicity is one of the major factors that limit plant growth and development in many acid soils which differs strikingly in their chemical form. Al has been shown to interfere with cell division in plant roots, decrease root respiration, increase cell wall rigidity and interfere with the uptake and transport of Ca, Mg, K, P and water supply to plants, alter cell-wall Donnan free space, the plasma membrane, membrane transport proteins etc. Al toxicity is mainly associated with severe changes in root morphology, resulting in curved, swollen, cracked, brownish, stubby and stiff root apices. It has been known that plants which exist in the presence of potentially toxic Al concentrations must be able to avoid direct contact of vital structures and metabolic processes with high activities of Al ions. The physiological mechanisms of Al resistance can either be mediated via exclusion of Al from the root apex or via intracellular tolerance of Al transported into the plant symplasm. The approaches like metal uptake and transportation in various plant parts, mechanism behind the interaction with mineral nutrients, specific genes responsible for tolerance levels and kinds of organic and amino acids which act as metal chelators and detoxifiers, level and forms of enzymes, and changes in root permeabilities to ions and molecules and their mechanisms are used to study Al toxicity in tolerant and sensitive plant genotypes.