Effects of Humic Acid on Antioxidant Defense System and Senescence-Related Gene Expression in Leaves of longiflorum × asiatic of Lilies (LA Lilium Hybrid)

Humic acids are derivatives of natural organic matter that are effective in promoting plant growth and development. Due to the importance of leaf durability in cut flowers, this study was performed on lily flowers with the aim of determining humic acid’s effects on leaves. The plants were treated with humic acid in two stages: bud development and the beginning of flower senescence. The leaves were harvested 72 h after treatment. First, the effect of humic acid on the expression of four senescence-dependent genes, CYP , LOX , NAC2 , and EIN2 , was investigated in leaves. Then, the activity of four enzymes, peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase, was investigated. Also, soluble solids and soluble sugars, protein, and malondialdehyde were measured in leaves. The results showed that the senescence process decreased under humic acid treatment. The expression of the CYP gene decreased by 13.6-fold in the bud development stage and 11.2-fold in the senescence stage. The NAC2 and EIN2 gene expressions increased 7.8- and 8.3-fold in the senescence stage, respectively. The activity of all antioxidant enzymes increased under the effects of humic acid at least one stage of treatment. Catalase activity showed a 100% increase in the senescence stage. Also, soluble solids (7.6%) and soluble sugars (18.5%) decreased. The results of this study indicate the inhibitory role of humic acid in the aging of lily leaves and help to increase the lifespan of the leaf.