Polyamines have been related to the ''Crassulacean Acid Metabolism'' (
CAM) in higher plants. Such relationship was however observed in plant
s where CAM activity is inducible by external factors. Results present
ed here indicate that, in Opuntia F. indica, cladodes where onset of C
AM is dependent on internal conditions, i.e. leaf age, the concentrati
on of putrescine increases in parallel to the acidity of the cytoplasm
. The parallel increase of putrescine concentration and acidity (malic
acid concentration) can be best evaluated during the onset of CAM (yo
ung cladodes), while such correlation is not observed in mature cladod
es where CAM is already in it's full function. Spermidine and spermine
show no correlation with CAM activity neither during the onset of CAM
nor during it's full function. However, spermidine levels correlate n
egatively to CAM activity when cladodes attain > 30 days of age. The r
esults suggest that putrescine in free form could possibly counteract
the increase of cellular acidity during onset of CAM in Opuntia F. ind
ica; the possible roles of spermidine are discussed.