Re: Aquatic Plants Digest V2 #480

Marshall Wilkinson writes:

>Best of luck on your substrate draft. As to your question about
>the effects of K in water and substrate. Assuming that ion
>transport in plants obeys the same laws as in animal cells the
>effects of accumulating K will be to depolarize the cell
>membranes. The potential difference (in mV) across the membrane
>provides the energy gradient for the transport of ions in and out
>of cells. So when external K gets high (> 10mM) membrane
>transport should be effected. In fish high potassium will cause
>their muscles to work poorly and with increasing concentrations
>eventually death. I could be way off here assuming the
>predominate membrane potential producing ion in plants is K, it
>certainly is in animals.
>Any hardcore botanists out there that can educate me (us)?

In plants and even algae, the predominate membrane potential producing ion is 
the hydrogen ion. There is actually an enzyme in the cytoplasmic membrane (the  
membrane that encloses the cell) called hydrogen-ATPase (ATP stands for 
adenosine triphosphate. ATPases are enzymes that use ATP, the energy source 
in all living cells, to carry out their cellular functions). Its function is to pump 
hydrogen ions to the outside of the cell. A charge difference is set up by the 
difference in concentration of H+ ions between the inside and the outside of the 
cell. This creates the membrane potential needed to supply energy for the 
transport of other nutrients, etc., into or out of the cell via other enzymes in the 
cytoplasmic membrane. Alot of people are working on the characterization of this 
enzyme in many species of plants and algae because of its important role. Most 
researchers are interested in how its activity is regulated, among other things.

Just my 2 cents worth.

Robb D. VanPutte
Dept. of Biology
Texas A&M University