The diamine putrescine, the triamine spermidine and the tetramine spermine occur as free cations and as conjugates with phenolic acids and macromolecules in plants. Their levels of concentration increase greatly when the environment suffer changes; specially when there is potassium deficiency, water deficits, salinity stress, anaerobiosis and acid stress ("Polyamines"). Because polyamines are synthesized by amino acid decarboxylation reactions, where H+ is consumed, levels of polyamines may function as a protection method; that is haw they conserve the pH values constant ("Polyamines"). Polyamines are alsoprecursors of various alkaloids that are important in plants defense.

Polyamine	Structure	Occurrence
Putrescine	NH2(CH2)3NH2	Widespread
Cadaverine	NH2(CH2)5NH2	Restricted
Spermidine	NH2(CH2)3NH(CH2)4NH2	Widespread
Spermine	NH2(CH2)3NH(CH2)4NH(CH2)3NH	Widespread

("Polyamines")
    
The first polyamine formed is putrescine. This may happen by decarbosylation of ornithine or arginine.  These reactions are catalyzed by the enzymes orthinine decarboxylase (ODC) or arginine decarboxylae (ADC), respectively. The polyamines spermidine and spermine are formed by adding an aminopropyl moeity to putrescine and spermine, respectively.

Polyamines can occur as free molecular bases in plant cells, but they also occur as conjugates, associated with small molecules like phenolic acids and macromolecules such as proteins.  Polyamines are most commonly conjugated to cinnamic acids, preferentially p-coumaric, ferulic and caffeic acids, and they occur in a wide range of plant families. 

Adequate levels of polyamines are necessary for optimal growth and replication of plants, bacteria and fungi.("Polyamines")
 


Assay of enzyme activities ( ADC, ODC and SAMDC )(Burtin and Michael) :

• Frozen leaf powder is homogenized in 0n1 M Hepes buffercontaining 10 mM dithiothreitol, 10 mM EDTA, 0n1 mM pyri-doxal 5h-phosphate and 0n5% (w\v) ascorbic acid.
• Insolublepoly(vinyl pyrrolidine) (100 mg\g of powder) is added beforehomogenization.
• The homogenates are  centrifuged for 25 minat 17000g and the supernatants loaded on to a PD10 column (Pharmacia) and eluted with the same buffer minus the ascorbicacid.
• The eluates are used for analysis of enzyme activity
• Enzyme reaction mixtures contains 100 µl of extract and 20 µl of radiolabelled substrate
• The ODC assay mixture contains 0n1 µCi of -[1-14C]ornithine (57 mCi\mmol) and unlabelledornithine (2n5 mM). -[U-14C]arginine (0n1 µCi, 307 mCi\mmol) and unlabelled arginine (1n25 mM final concentration) are added for the analysis of ADC activity.
• For SAMDC activity, 20 µl of 5 µCi\mlS-adenosyl- -carboxy[14C]methionine dilutedin 4n5 mM unlabelled SAM is used.
• Each reaction is performed in duplicate at 37 mC for 45 min
• The ADC, ODC andSAMDC activities are determined by measurement of 14CO2 released from substrates

Reference:
Slocum, Robert D.  Flores, Hector E.  “Biochemistry and Physiology of Polyamines in Plants.” CRC PRESS. 1991
"What are polyamines?" The Scottish Agricultural College online: http://www.sac.ac.uk/plantsci/External/Research/Polyamines.htm
Burtin, Daniel and Michael, Anthony J. "Overexpression of arginine decarboxylase in transgenic plants" online: http://www.biochemj.org/bj/325/0331/3250331.pdf
http://www.bspp.org.uk/icpp98/1.2/21.html