Re: what effects does detergent have on plants?

The effect of detergent on plants varies depending on how the plant is 
exposed to it.  Lets take two examples:

1)  Plant is sprayed with detergent solution, to cover all the leaves.

    The detergent will remove the waxy coating on the leaves of the plant. 
 The plant uses this wax to make the leaves waterproof, and to stop 
pathogens getting at the leaf.  If a high concentration of detergent is 
used, the detergent will remove the cell membrane of the the leaf cells, 
killing them.  Even at lower concentrations, death of the leaves is likely 
as they will dry out without their protective waxes. Have a look at the 
picture of a plant leaf - you can see this wax as a fuzzy coat (especially 
in the third picture). 

Scanning electron micrographs of a plant leaf

2) Plant is watered with detergent solution.

   This time the detergent goes straight to the roots.  The roots don't 
have any waxy cuticle, as their function is to absorb water.  They also 
have to absorb a number of other things, and make sure that water doesn't 
leak out of the plant to the soil.  The detergent will dissolve the lipid 
membrane that surround the root cells.  This will kill these outer cells, 
and stop the plant absorbing water and nutrients.  The root hair cells 
absorb all of the water and nutrients the plant needs, and these will be 
the first to be killed by detergent.  Without its' supply of water and 
nutrients, the plant will die.  Have a look here at some root hair cells at 
this site:

A group of scientists working on root hairs

Hope this helps,
Carl