A study on the photosynthetic pigments and phenolic compounds of safflower in response to foliar application of melatonin under water deficit condition

In order to study the effect of melatonin foliar application on photosynthetic pigments’ composition, phenolic compounds and soluble sugars on plants grown from different seed quality of safflower under water deficit condition, two field trials were conducted at Aburaihan Campus, University of Tehran in 2017 and 2018 growing seasons. The experimantal design was split-factorial randomized complete block design with four replicates. The treatments consisted of two levels of drought stress (1- normal irrigation (no-stress) and 2- irrigation after reaching 85% of soil moisture depletion of field capacity at flowering stage (drought stress)) were randomized to the main plots. Subplots were 4 treatments in number and consisted of a factorial combination of seed quality (1-stored seed and 2-recently harvested seeds) and foliar application (1-control (distilled water foliar application) and, 2- melatonin foliar application at 0.2 Mm concentration). The results showed that plant grown from recently harvested seed positively response to melatonin foliar application and this led to increase in chlrophyll a content by 33.33 % in comparison with control (distilled water foliar application). Also the results indicated that melatonin foliar application was successful to increase the flavonoids content only under non-stress condition over two seed quality treatments but on the contraty decreased flavonoids content under water deficit condition. The results demonstrated that melatonin foliar application decreased soluble sugars over both water deficit treatments. It’s seems that melatonin foliar application ameliorated the severity of stress because of its antioxidative charachteristic and provide an unstressed environment for plant so that there is no need to increase the level of metabolites that usually increased under drought condtition.