Effects of polyamines on cadmium- and copper-mediated alterations in wheat (Triticum aestivum L) and sunflower (Helianthus annuus L) seedling membrane fluidity.

We investigated if wheat (Wh) and sunflower (Sf) plants watering with 1 mM CdCl or CuCl for 5-15 d during germination and seedling altered membrane fluidity (MF) of their leaves and roots, and if plant pre-treatment with the polyamines (PAs) putrescine (Put), spermidine (Spd) or spermine (Spm) prevented those alterations. Cd impaired Wh and Sf growth, while Cu only affected Sf growth. Cu and Cd increased MF of leaves of both plant species, while Cd decreased MF of Sf roots. Plant treatment for 15 d with 0.1 mM Put, Spd or Spm did not affect plant growth and had opposed effects on the MF of both plants. Finally, Wh and Sf were pre-treated with PAs for either 5 or 10 days followed by metal treatment until day 15. While Put did not affect membrane MF, Spd and Spm decreased it between 5 and 10 d of plant treatment. Together, experimental results demonstrate that during plant development (a) Cd and Cu have noxious effects on plants membrane biophysical properties that could be partially responsible of their toxicity, and (b) this deleterious effect could be only partially prevented by plant pretreatment with the PAs.