MadSci Network: Botany

Re: Why do roots require calcium ions for normal functioning?

Date: Thu Feb 6 20:55:16 2003
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1044446129.Bt

External calcium ions (Ca++) are required to maintain cell membrane integrity. 
Without external calcium, cell membranes become "leaky" and lose ions they 
previously absorbed. Their ion uptake is also reduced. Other positively-charged 
ions (cations) can displace calcium ions from the negatively-charged cation 
exchange sites on the cell membrane.

External calcium also protects roots from low pH injury which is due to 
hydrogen ions (H+) and injury from other cations, such as ammonium (NH4+) and 
sodium (Na+). Plant roots often excrete a lot of H+ to balance out any excess 
postively-charged ions they have absorbed.

Ca++ is a very important ion in many plant cellular processes including 
cytoplasmic streaming and cell division. The latter should not be surprising 
because cell walls contain lots of calcium pectates. 

Calcium is a phloem-immobile mineral nutrient, meaning once absorbed by the 
plant and transported in xylem, it is not redistributed to other parts of the 
plant via the phloem. Mobile mineral nutrients, such as nitrogen and 
phosphorus, can be redistributed in plants via the phloem when there is a 
deficiency. Continuous uptake by the roots is not required for phloem-mobile 
mineral nutrients.  

Calcium deficiency symptoms occur first in growing points, such as shoot tips 
and root tips, which have meristems where cell division occurs. So one reason 
calcium is required in the external solution is that the plant must constantly 
absorb calcium to keep growing. It cannot redistribute calcium already 
deposited in the plant to the growing points. The first website found 
that "calcium ion influx through plasma membrane channels is required for 
normal root hair growth." 

The Ca++ level in the cell cytosol is also very important in signal tranduction 
in plants. Calcium is considered a secondary messenger in many plant processes 
(see second website).

External calcium is also required fro pollen tube germination and growth.


Calcium and plant roots

A Second Messenger: Calcium Ions

Calcium Nutrition of Cotton

Epstein, E. 1972. Mineral Nutrition of Plants: Principles and Perspectives. New 
York: Wiley.

Cation Exchange

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