The study of callus induction and effect of salicylic acid on callus secondary metabolites of Juniperus excels

Juniperus excelsa is a light demanding and long-lived tree species of the Cupressaceae family. This species has been shown good tolerant to harsh conditions such as cold and drought situations.  This research aims to assess the effect of different concentrations of auxin and cytokinin on callus induction of J. excelsa asfactorial based on completely randomized block design and to study the effect of salicylic acid on phenol, flavonoid and inhibition of DPPH radicals of calli. The explants were selected from sound trees with no diseases and pests. Woody plant medium (WPM) was selected with same laboratory conditions (experimental place, temperature, explant age, hormone type). The experimental treatments were auxin with 5 levels (0, 1 mg/l NAA, 2 mg/l NAA, 1 mg/l 2, 4-D, and 2 mg/l 2,4-D), and cytokinin with 3 levels (0, 0.25 mg/l Kin, 0.5 mg/l kin). The results showed the explants gradually swelled after 3 weeks, and completely induced callus after 6 weeks. The interaction of auxin and cytokinin hormones showed that the highest amount of callus induction (80%) was obtained in the interaction of 0.25 mg/l Kin and 1 mg/l NAA. The highest fresh weight of callus was in the interaction of 0.25 mg/l and 1 mg/l NAA as 1.1 gr. Besides, the dry weight of callus was recorded in the interaction of 0.25 mg/l Kin and 1 mg/l NAA. Kin combined with NAA caused the formation of compressed and yellow callus, and Kin combined with 4, 2-D, created a friable and green callus. On the other hand, we found that the total phenol content in 100 µM SA (31.8 mg gallic acid/ grDW) was higher than other treatments. There was no significant difference between control and 50 µM SA. The highest (9.3 mg quercetin / grDW) and lowest (2.05 mg quercetin / grDW) flavonoid contents were found in 100 µM SA and control, respectively.  In addition, the maximum inhibition of DPPH was recorded in 100 µM SA (35.06%), while the minimum was observed in control (25.3%).