Aluminum-Accumulating Plants


Aluminum-Accumulating Plants
Beneficial Effects of Aluminum in Plants
  Growth Stimulation
  Inhibition of Plant Pathogens
Aluminum Absorption and Transport within Plants
  Phytotoxic Species
  Aluminum Speciation in Symplasm
  Radial Transport
Aluminum Toxicity Symptoms in Plants
  Short-Term Effects
    - Inhibition of Root Elongation
    - Disruption of Root Cap Processes
    - Callose Formation
    - Lignin Deposition
    - Decline in Cell Division
  Long-Term Effects
    - Suppressed Root and Shoot Biomass
    - Abnormal Root Morphology
    - Suppressed Nutrient Uptake and Translocation
    - Restricted Water Uptake and Transport
    - Suppressed Photosynthesis
    - Inhibition of Symbiosis with Rhizobia
Mechanisms of Aluminum Toxicity in Plants
  Cell Wall
    - Modification of Synthesis or Deposition of Polysaccharides
  Plasma Membrane
    - Binding to Phospholipids
    - Interference with Proteins Involved in Transport
      - H+ -ATPases
      - Potassium Channels
      - Calcium Channel
      - Magnesium Transporters
      - Nitrate Uptake
      - Iron Uptake
      - Water Channels
    - Signal Transduction
      - Interference with Phosphoinositide Signal Transduction
      - Transduction of Aluminum Signal
    - Disruption of the Cytoskeleton
    - Disturbance of Calcium Homeostasis
    - Interaction with Phytohormones
      - Auxin
      - Cytokinin
    - Oxidative Stress
    - Binding to Internal Membranes in Chloroplasts
    - Binding to Nuclei
Genotypic Differences in Aluminum Response of Plants
  Screening Tests
Plant Mechanisms of Aluminum Avoidance or Tolerance
  Plant Mechanisms of Aluminum Avoidance
    - Avoidance Response of Roots
    - Organic Acid Release
    - Exudation of Phosphate
    - Exudation of Polypeptides
    - Exudation of Phenolics
    - Alkalinization of Rhizosphere
    - Binding to Mucilage
    - Binding to Cell Walls
    - Binding to External Face of Plasma Membrane
    - Interactions with Mycorrhizal Fungi
  Plant Mechanisms of Aluminum Tolerance
    - Complexation with Organic Acids
    - Complexation with Phenolics
    - Complexation with Silicon
    - Sequestration in Vacuole or in Other Organelles
    - Trapping of Aluminum in Cells
Aluminum in Soils
  Locations of Aluminum-Rich Soils
  Forms of Aluminum in Soils
  Detection or Diagnosis of Excess Aluminum in Soils
    - Extractable and Exchangeable Aluminum
    - Soil-Solution Aluminum
  Indicator Plants
Aluminum in Human and Animal Nutrition
  Aluminum as an Essential Nutrient
  Beneficial Effects of Aluminum
    - Beneficial Effects of Aluminum in Animal Agriculture
    - Beneficial Uses of Aluminum in Environmental Management and Water Treatment
  Toxicity of Aluminum to Animals and Humans
    - Toxicity to Wildlife
    - Toxicity to Agricultural Animals
      - Toxicity to Ruminants (Cattle and Sheep)
      - Toxicity to Poultry
    - Toxicity to Humans
      - Overview of Aluminum Metabolism
      - Overview of the Biochemical Mechanisms of Aluminum Toxicity
Aluminum Concentrations
  In Plant Tissues
    - Aluminum in Roots
    - Aluminum in Shoots
  Soil Analysis
Relative to aluminum accumulation, there appears to be two groups of plant species: aluminum excluders and aluminum accumulators (8). Most plant species, particularly crop plants, are aluminum excluders. Aluminum contents in most herbaceous plants averaged 200 mg kg-1 in leaves (Hutchinson, cited in [9]). Chenery (10,11) analyzed leaves of various species of monocots and dicots for aluminum content, and defined aluminum accumulators as those plants with 1000 mg Al kg-1 or greater in leaves. Aluminum accumulation appears to be a primitive character, found frequently among perennial, woody species in tropical rain forests (9,12).

Masunaga et al. (13) studied 65 tree species and 12 unidentified species considered to be aluminum accumulators in a tropical rain forest in West Sumatra and suggested that aluminum accumulators be divided further into two groups: (a) those with aluminum concentrations lower than 3000 mg kg-1; and (b) those with higher aluminum concentrations. For trees with foliar aluminum concentrations greater than 3000 mg kg-1, positive correlations were noted between aluminum concentrations and phosphorus or silicon concentrations in leaves.

Although Chenery (11) did not consider gymnosperms to be aluminum accumulators, Truman et al. (14) proposed that most Pinus species are facultative aluminum accumulators. In Australia, values of foliar aluminum ranged from 321 to 1412 mg kg-1 for Monterey pine (Pinus radiata D. Don), 51 to 1251 mg kg-1 for slash pine (Pinus elliotii Engelm.), and 643 to 2173 mg kg-1 for loblolly pine (Pinus taeda L.) (15). In addition, foliar aluminum concentrations≥1000 mg kg-1 were reported in Monterey pine and black pine (Pinus nigra J.F. Arnold) grown in nutrient solutions containing aluminum (14,16,17).

Tea (Camellia sinensis Kuntze) is one crop plant considered to be an aluminum accumulator, with aluminum concentrations of 30,700 mg kg-1 in mature leaves, but much lower concentrations of only 600 mg kg-1 in young leaves (18). Most of the aluminum was localized in the cell walls of the epidermis of mature leaves (18).

Another well-known aluminum-accumulating plant is hydrangea (Hydrangea macrophylla Ser.), which has blue-colored sepals when the plant is grown in acidic soils and red-colored sepals when grown in alkaline soils. The blue color of hydrangea sepals is due to aluminum complexing with the anthocyanin, delphinidin 3-glucoside, and the copigment, 3-caffeoylquinic acid (19). Two excellent reviews of aluminum accumulators are by Jansen et al. (9) and Watanabe and Osaki (8). Possible mechanisms of aluminum tolerance will be discussed in later sections.