Isabel Corrales

A glance into aluminum toxicity and resistance in plants.

Aluminum toxicity is an important stress factor for plants in acidic environments. During the last decade considerable advances have been made in both techniques to assess the potentially toxic Al species in environmental samples, and knowledge about the mechanisms of Al toxicity and resistance in plants. After a short introduction on Al risk assessment, this review aims to give an up-to-date glance into current developments in the field of Al toxicity and resistance in plants, also providing sufficient background information for non-specialists in aluminum research. Special emphasis is paid to root growth and development as primary targets for Al toxicity. Mechanisms of exclusion of Al from sensitive root tips, as well as tolerance of high Al tissue levels are considered.

Different Effects of Aluminum on the Actin Cytoskeleton and Brefeldin A-Sensitive Vesicle Recycling in Root Apex Cells of Two Maize Varieties Differing in Root Elongation Rate and Aluminum Tolerance

A relationship between aluminum (Al) toxicity, endocytosis, endosomes and vesicle recycling in the root transition zone has recently been demonstrated. Here the importance of filamentous actin (F-actin)-based vesicle trafficking for Al tolerance has been investigating in maize varieties differing in their Al sensitivities. More Al was internalized into root tip cells of the Al-sensitive variety 16x36 than in the Al-tolerant variety Cateto. The actin cytoskeleton and vesicle trafficking were primary targets for Al toxicity in the root tips of the sensitive variety. Visualization of boron-cross-linked rhamnogalacturonan II (RGII)-containing brefeldin A (BFA) compartments revealed that Al inhibited the formation of these compartments, especially in variety 16x36. The time sequence of Al effects on pectin recycling matches the growth effects of Al in this sensitive variety. These results support the hypothesis that Al binding to pectin-rich cell walls can contribute to reversible inhibition of root elongation. Al-induced alterations on F-actin were most evident in the central part of the transition zone of Al-sensitive 16x36, where Al was localized inside the nucleoli. In relation to this observation, a role for symplastic Al in both irreversible growth inhibition and amelioration of BFA-induced inhibition of root elongation is discussed.

Influence of silicon pretreatment on aluminium toxicity in maize roots

The influence of Si pretreatment on Al toxicity in an Al sensitive maize variety (Zea mays L. var. BR 201 F) was investigated using root elongation rates (RER) and hematoxylin staining as stress indicators. Plants pretreated with 1 mt M Si (+ Si) and then exposed for 24 h to Al in nutrient solution without concurrent Si supply in the rooting medium exhibited higher RER than plants that were not pretreated with Si (-Si). The ameliorative effect of Si was due to lower Al uptake and to the exclusion of Al from the root tips in + Si plants. Lower Al uptake in + Si plants was not a consequence of decreased Al availability in the bulk solution. The possible mechanisms of Si-induced increase of Al resistance are discussed

Phosphorus Efficiency and Root Exudates in Two Contrasting Tropical Maize Varieties

ABSTRACT Nutrient solution culture and quartz sand amended with or without rock phosphate, were used to compare the short-term responses to phosphorus (P) deficiency of two contrasting maize hybrids, L3x228-3 (P-efficient) and HS 2841x5046 (P-inefficient). In solution-grown seedlings, the rapid P deficiency-induced enhancement of root growth and of the root/shoot ratio was a sign of P deficiency stress rather than of P efficiency. In sand culture, uptake of P from sparingly soluble rock phosphate was higher in P-efficient plants than in P-inefficient maize. In the variety L3-228-3, P efficiency seemed due to enhanced P acquisition rather than to an enhanced P use efficiency. In sand, but not in solution culture, higher citrate concentrations were detected in the rhizosphere of P-efficient than of P-inefficient maize. Quartz sand amended with rock phosphate was a better substrate than nutrient solution for revealing the varietal differences in P acquisition efficiency in short-term experiments.

Root Behavior in Response to Aluminum Toxicity

Roots have an extraordinary capacity for adaptive growth which allows them to avoid toxic soil patches or layers and grow into fertile sites. The response of roots to aluminum toxicity, a widespread problem in acid soils, is an excellent model system for investigating the mechanisms that govern this root behavior. In this review, after a short introduction to root growth movement in response to chemical factors in the soil, we explore the basic mechanisms of Al-induced inhibition of root growth. The actinomyosin network and endocytic vesicle trafficking are highlighted as common targets for Al toxicity in cell types with quite different origins: root tip transition zone cells, tip-growing cells like root hairs or pollen tubes, and astrocytes of the animal or human brain. In the roots of sensitive plants, the perception of toxic Al leads to a change in root tip cell patterning. The disturbance of polar auxin transport by Al seems to be a major factor in these developmental changes. In contrast, Al activates organic acid efflux and the binding of Al in a nontoxic form in Al-resistant genotypes.