Effect of 5- aminolevulinic acid on changes of water deficit stress tolerance index and catalase activity of sweet pepper seedlings (Capsicum annuum L. cv. red bell pepper)

To study the effect of 5- aminolevulinic acid (ALA) on some physiological responses of sweet pepper under drought stress, a factorial experiment in a randomized complete block design with 5- aminolevulinic acid and water deficit stress treatments was carried out in the greenhouse of the agricultural faculty of Ilam University. Levels of water deficit stresswere stress free conditions (irrigation within the field capacity), moderate stress (irrigation within the 60% field capacity) and severe water deficit stress(irrigation within the 30% field capacity). Four concentrations of AL Aincluding 0 (control), 0.25, 0.5, and 1 mM were applied as foliar application at three to four-leaf stage. The results showed that with increasing ALA concentrations, catalase activity, proline content, relative water content, dry weight, flower and fruit number increased but electrolyte leakage (EL) decreased. The lowest EL and the highest proline content, relative water content, fruit number and shoots fresh weight were observed at 1 mM of ALA while the highest catalase activity, dry weight and flower number were obtained with application of 0.5 mM ALA. Water deficit stressdecreased relative water content, fresh and dry weight, flower and fruits numbers, but increased EL, proline content and catalase activity. ALA with increasing of catalase activity and reducing of EL reduced the stress effects on plant growth and yield. According the results of this experiment, through the impact on growth characteristics and biochemical and physiological parameters, ALA provides better water deficit stresstolerance in pepper plants.