Responses of antioxidant defense system of <Emphasis Type="Italic">Helianthus annuus</Emphasis> to abscisic acid treatment under drought and waterlogging

The effect of abscisic acid (ABA) treatment on growth pigments and antioxidant defense system were investigated in seedlings of Helianthus annuus (cvs. Nantio F1 and Özdemirbey) subjected to drought and waterlogging stress. In addition, seedlings were sprayed with 10 M ABA three times every other day. Relative growth rate (RGR) was significantly reduced in both genotypes under drought stress, however, this growth inhibition was less in ABA-treated plants. Total chlorophyll content increased by drought stress in both genotypes. Ascorbate was not influenced by drought, while α-tocopherol increased in cv. Nantio F1. Ascorbate and α-tocopherol increased with drought stress in cv. Özdemirbey. ABA treatment decreased ascorbate and β-carotene contents while it increased α-tocopherol and xanthophylls contents under drought stress. The activity of superoxide dismutase (SOD) in both genotypes increased under drought stress-ABA combinations. Catalase (CAT) activity decreased under drought stress and drought-ABA combinations while it increased under waterlogging stress. Glutathione reductase (GR) activity decreased under drought stress but recovered with ABA treatment. The results suggested that ABA treatments have different effects on the components of antioxidant defense system in H. annuus genotypes and ABA may contribute drought-induced oxidative stress tolerance but not effects under waterlogging stress.