  The protective effect exerted by polyamines (Put and Spd) against cadmium
(Cd) stress was investigated in Brassica juncea plants. Treatment with CdCl2
(75 micro-Mole) resulted in a rise of Cd accumulation, a decrease of fresh and
dry weights in every plant organ, an increase of free polyamine content at limb
and stem levels as well as a decrease at root level. On the other hand, the
total conjugated polyamine levels in the stem tissues were unaffected by Cd. In
the leaf tissues, this metal caused a reduction of chlorophyll a content, a
rise of guaiacol peroxidase (GPOX) activity and an increase of malondialdehyde
(MDA), soluble glucide, proline and amino acid contents. Exogenous application,
by spraying, of putrescine (Put) and spermidine (Spd) to leaf tissues reduced
CdCl2-induced stress. These polyamines proved to exert a partial, though
significant, protection of the foliar fresh weight and to alleviate the
oxidative stress generated by Cd through reductions of MDA amounts and GPOX
(E.C.1.11.1.7) activity. The enhancement of chlorophyll a content in plants by
Put and those of Chl a and Chl b by Spd both constitute evidences of their
efficacy against the Cd2+-induced loss of pigments. Conversely to Put, Spd
caused a decrease of Cd content in leave tissues and a rise in the stems and
roots; these findings are in favour of a stimulation of Cd uptake by Spd. The
proline stimulation observed with Cd was reduced further to the spraying of Put
onto tissues, but the decrease induced by Spd was more limited. In the plants
treated with Cd, the amino acid contents in the leaves were unaffected by Put
and Spd spraying; on the other hand, Cd2+ disturbed polyamine levels (free and
acido-soluble conjugated-forms); we notice the rise of total free PAs and the
decrease of their conjugated-ones.
