Re: What does the phosphatase enzyme in plants do?

	Phosphate groups in ALL organisms is the major covalent modification of 
proteins and carbon substrates that allows for the regulation, organization 
and efficency of most biochemical pathways within the cell.  
Phosphate is also a central part of the major molecule within the cell (ATP 
and GTP) that sequesters and stores energy for use in chemical reactions.  
The cell (in both plants and animals) produces many proteins (enzymes) which 
are specialized for transfering phosphate groups.  Phosphatases REMOVE 
phosphate groups and Kinases ADD phosphate groups (by transfering it FROM 
ATP to a substrate). These specialized enzymes are needed to direct the 
transfer of phosphate from one substrate to another.  
	A biochemical pathways are regulated by phosphoryl group transfers.  An 
enzyme required to catalyze a particular reaction in the pathway may only 
recognize and bind to the phosphorylated form of a particular substrate 
compound. Therefore,  the pathway is inhibited until the molecule is 
phosphorylated (or "activated"), and that enzyme is said to be "specific" 
for the phosphorylated form of the substrate.  Also, phosphoryl groups are 
used to "energize" a substrate or reactant in a biochemical pathway.  A 
reaction may not be energenicaly favorable until a phosphate group (ATP) is 
added to the reaction.  The energy stored in the form of a chemical bond 
between the last two phosphate groups of ATP (the beta and gamma phosphates) 
is released and utilized by the enzyme to drive the energenitcally 
unaforable reaction foward.  (the large amount of energy given off by 
breaking this bond and the ease in breaking it are major reasons why ATP is 
the major energy "coin" within the cell).  In the plant cell, for example, 
the Calvin Cycle is a main biochemical pathway the plant uses to produce its 
own "food" from CO2 (called carbond fixation).  In this pathway, Kinases are 
used to add phosphate (from ATP) to Ribulose 1 phosphate to produce 
Ribuloase 1,5 bis phosphate (RUBP). This reaction is required to "activate" 
RUBP for future ("down-stream") reactions.  Phosphatases are also used in 
this pathway such as Fructose 1,6 bisphosphatase to create fructose 6 
phosphate.  
	Once phosphates are removed from a substrate, the free phosphate groups 
add to the concentration of free phosphate within the cell and will soon 
become incorporated into another ATP (or GTP) molecule.  The rate of turn-
over of ATP molecules within the cell is high.  Phosphate groups are rapidly 
being added to ADP and released.  Also, as the concentration of free 
phosphate increases within the cell, the rate of ATP production also 
increases, so that the cell is not depleated of this important molecule.

	I hope this helps!  consult a Biochemistry textbook (I recommend 
Stryer) if you have any further interests/questions.