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  Section: Plant Nutrition » Macronutrients » Calcium
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Other Effects of Calcium on Plants

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

It has been known for a long time that calcium is essential for the growth of pollen tubes. A gradient of cytoplasmic calcium concentration occurs along the pollen tube, with the highest concentrations being found in the tip. The fastest rate of influx of calcium occurs at the tip, up to 20 pmol cm-2 s-1, but there are oscillations in the rate of pollen tube growth and calcium influx that are approximately in step (32). It seems probable that the calcium exerts an influence on the growth of the pollen tube mediated by calmodulin and calmodulin-like domain protein kinases (25), but the growth and the influx of calcium are not directly linked as the peaks in oscillation of growth precede the peaks in uptake of calcium by 4 s (32). Root hairs have a high concentration of Ca2+, and root hair growth has a similar calcium signature to pollen tube growth (24). Slight increases in cytoplasmic Ca2+ concentration can close the plasmodesmata in seconds, with the calcium itself and calmodulin being implicated (33). Many sinks, such as root apices, require symplastic phloem unloading through sink plasmodesmata, so this action implies that calcium has a role as a messenger in the growth of many organs.

It seems that calcium can be replaced by strontium in maize to a certain extent (34), but despite the similarities in the properties of the two elements, this substitution does not appear to be common to many plant species. In general, the presence of abundant calcium in the soil prevents much uptake of strontium, and in a study on 10 pasture species, the concentration of strontium in the shoot was correlated negatively with the concentration of calcium in the soil (35).

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