Nitrogen is contained in all enzymes essential for all plant functions. Phosphorus A component of the compound within plants which supply the energy to grow and maintain the plant. Part of cell membranes, the structures which selectively keep out unneeded compounds and allow in those compounds which are needed for the plant cells to function correctly. A part of DNA and its relatives. Needed for cell division and for reproduction.
Potassium Activates certain enzymes.
It regulates stomate opening, which in turn regulates air flow into the leaf and transpiration of water out of the leaf. It regulates turgor pressure, which helps protect plant cells from disease invasion. In certain plants, potassium can be replaced by sodium. Sulfur Sulfur is a part of certain amino acids and all proteins. It is a part of the flavor compounds in mustard and onion family plants.