Interactions with Phytohormones


Historical Information
  Determination of Essentiality
Functions in Plants
  Effects on Membranes
  Role in Cell Walls
  Effects on Enzymes
  Interactions with Phytohormones
  Other Effects
Diagnosis of Calcium Status in Plants
  Symptoms of Deficiency and Excess
  Concentrations of Calcium in Plants
    - Forms of Calcium Compounds
    - Distribution of Calcium in Plants
    - Calcicole and Calcifuge Species
    - Critical Concentrations of Calcium
    - Tabulated Data of Concentrations by Crops
Assessment of Calcium Status in Soils
  Forms of Calcium in Soil
  Soil Tests
  Tabulated Data on Calcium Contents in Soils
Fertilizers for Calcium
  Kinds of Fertilizer
  Application of Calcium Fertilizers

An involvement of calcium in the actions of phytohormones seems likely as root growth ceases within only a few hours of the removal of calcium from a nutrient solution (22). The element appears to be involved in cell division and in cell elongation (27) and is linked to the action of auxins. The loosening of cellulose microfibrils in the cell wall is controlled by auxins, giving rise to excretion of protons into the cell wall. Calcium is involved in this process, as discussed earlier. Furthermore, auxin is involved in calcium transport in plants, and treatment of plants with the indoleacetic acid (IAA) transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA), results in restricted calcium transport into the treated tissue (28). As the relationship is a two-way process, it cannot be confirmed easily if calcium is required for the action of IAA or if the action of IAA gives rise to cell growth, and consequent cell wall development, with the extra pectic material in the cell wall then acting as a sink for calcium. It is also possible that IAA influences the development of xylem in the treated tissue (29).

Increase in shoot concentrations of abscisic acid (ABA) following imposition of water-deficit stress leads to increased cytoplasmic concentration of Ca2+ in guard cells, an increase that precedes stomatal closure (24). Further evidence for an involvement of calcium with phytohormones has come from the observation that senescence in maize (Zea mays L.) leaves can be slowed by supplying either Ca2+ or cytokinin, with the effects being additive (30). There is also a relationship between membrane permeability, which is strongly affected by calcium content and ethylene biosynthesis in fruit ripening (31).