The ameliorative effect of salicylic
acid (SA: 0.5 mM) on sunflower (Helianthus
annuus L.) under Cu stress (5 mg l
–1
) was studied.
Excess Cu reduced the fresh and dry weights of
different organs (roots, stems and leaves) and
photosynthetic pigments (chlorophyll a, b and
carotenoids) in four-week-old plants. There was a
considerable increase in Chl a/b ratio and lipid
peroxidation in both the roots and leaves of plants
under excess Cu. Soluble sugars and free amino
acids in the roots also decreased under Cu stress.
However, soluble sugars in the leaves, free amino
acids in the stems and leaves, and proline content
in all plant organs increased in response to Cu
toxicity. Salicylic acid (SA) significantly reduced
the Chl a/b ratio and the level of lipid peroxida-
tion in Cu-stressed plants. Under excess Cu, a
higher accumulation of soluble sugars, soluble
proteins and free amino acids including proline
occurred in plants treated with 0.5 mM SA.
Exogenous application of SA appeared to induce
an adaptive response to Cu toxicity including