Aminolevulinic acid-induced changes in some key physiological attributes and activities of antioxidant enzymes in sunflower (Helianthus annuus L.) plants under saline regimes

Sodium chloride (150mM) applied through the root growing medium decreased leaf osmotic potential (psi(s)), while it considerably increased accumulation of leaf H2O2, glycinebetaine (GB), MDA contents and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) in sunflower plants. However, salt stress did not affect relative water content (RWC), leaf free proline (Pro) contents, efficiency of photosystem-II (F-v/F-m) and total leaf phenolics in sunflower plants. Foliar-applied 5-aminolevulinic acid (ALA) did not affect leaf psi(s), RWC, F-v/F-m, ratio, Pro, GB, MDA, total soluble proteins and phenolics as well as activities of POD and CAT enzymes. In contrast, varying levels (20, 50 and 80 mg L-1) of ALA considerably decreased leaf H2O2, i.e. 22.41, 54.66 and 77.06% at 20,50 and 80 mg L-1 ALA, respectively, while it increased SOD activity 18.06, 54.07 and 56.13% at 20,50 and 80 mg L-1 ALA respectively. Foliar-applied ALA did not have a substantial role in alleviating the adverse effects of salt stress on most of the physiological attributes associated with salt tolerance of sunflower plants under study. (C) 2012 Elsevier B.V. All rights reserved.