Aluminum toxicity and tolerance mechanism in cereals and legumes — A review

Abstract

Aluminum (Al), the third most abundant element overall, after silicon and oxygen, is found virtually in all food, air, soil and water. Under acidic conditions, Al is solubilized into [Al(H 2 O) 6 ] 3+ , which is highly toxic to many plant species. Present paper reviewed Al toxicity and tolerance mechanism in agricultural plants with special reference to cereals and legumes. Even at micromolar concentrations, cell division in the root tip meristem in sensitive plants is quickly inhibited by Al 3+ . Expressing the species-dependent manner of response, growth enhancement at low concentrations of Al 3+ is also reported from some plants such as soybean. Plasma membrane can be identified as the primary target of Al toxicity, where production of higher reactive oxygen species and higher fatty acid peroxidation has been observed due to alteration of plasma membrane integrity. Though, toxicity and the mechanisms attributed to Al-resistance are extremely complex phenomena, exclusion is widely accepted as the key mechanism involved in detoxifying Al 3+ . Exudation of chelating ligands, formation of pH barrier at the rhizosphere or at root apoplasm, cell wall immobilization, selective permeability of the plasma membrane, and Al efflux have been proposed as the possible mechanisms for Al exclusion. Al-induced exudation in cereals and legumes is dominated by citrate, malate, and oxalate in varying degrees depending on the species and/or cultivar. Apart from sensitive cultivars, moderately tolerant or tolerant cultivars can also be distinguished from various kinds of cereals and legumes. However, reliable techniques for screening such resistant genotypes have not been developed for any economically important crops.

Silicon in vascular plants: uptake, transport and its influence on mineral stress under acidic conditions

“…Aluminium is not a plant nutrient nor does it have any known function in metabolism (Arunakumara et al 2013). For a few plant species, however, it has been shown to have a beneficial effect on growth at low concentration (Broadley et al 2012).…”

Deep expression scrutiny of juxtaposed wild and cultivated lentil furnishes new insight into aluminium tolerance mechanism

“…Lentils grown on soils of low pH with Al toxicity suffers from lethal effects on host plant, rhizobia and their interaction, yet it shows no initial visual symptoms on the plant, apart from slow and stunted overall growth [3] It embarks stunting of roots, especially seminal roots and death of lateral roots due to sensitivity of plants, even at micro molar concentrations of Al 3+ . Therefore, cell division in root tip meristem is quickly inhibited [4]. Trimming of root biomass coaxed to impoverished uptake of water and nutrients.…”

“…Under stress condition, operating Al tolerance mechanisms are not same in all the species, besides, in certain species, different mechanisms can operate concomitantly producing tolerance through their amalgamated effects. Even though type of tolerance mechanisms for Al toxicity is disputed, yet exclusion is widely accepted as the key mechanism involved in detoxifying Al 3+ [4]. Thereby, to develop Al stress tolerant cultivars, an in depth understanding of divergent resistance mechanisms operating in lentil is crucial.…”

“…Protein TPX2 which is down-regulated in wild genotype under Al stress has microtubule binding capability and regulates pro-spindle assembly during late prophase and at the onset of mitosis[40,41]. Other down-regulated DEGs involves EXO70B1, which is encompassed in Golgi-independent membrane traffic to the vacuole and is a positive regulator of both abscisic acid (ABA)-promoted and mannitol (drought)-endorsed stomatal closure[42,43] Similarly, Vacuolar protein sorting-associated protein 54 chloroplastic is involved in pollen tube elongation and other polar growth[4]. Octanoyltransferase is essential for de novo plastidial protein lipoylation during seed development[45].…”

The residual effect of gypsum on subsoil conditioning, nutrition and productivity of sugarcane crops

“…These factors hinder development of the root system of several crops due to the fundamental role of calcium in cell division and growth of apical meristems (Marschner, 2012). Furthermore, calcium has low mobility in plants (White and Broadley, 2003), and aluminum, in high concentrations in the soil, is associated with several morphological and physiological abnormalities in the root tissues, resulting in lower absorption of water and nutrients (Arunakumara et al 2013). In the case of sugarcane, the roots play an essential role in the growth of ratoons because after harvest the energy and nutrients needed for regrowth are supplied by the root system, as mentioned by Trivelin et al (2002).…”