SUMMARY
In order to investigate the effects of some plant growth regulators on photosynthetic pigments and growth of fennel plants, a greenhouse experiment was conducted based on the randomized complete block design with three replicates in 2017. Treatments were the application of methyl jasmonate (25, 50, 100 and 200 µM), putrescine (0.25, 0.5, 1 and 2 mM) and 24-Epibrassinolide at 0.001, 0.01, 0.1 and 1 µM and distilled water as a control. The results indicated that application of 0.5 Mm putrescine, exhibited significant effects on the chlorophyll a (62%), b (104%), total chlorophyll (72%), carotenoids (51%), flavonoids (51%), anthocyanin content (-14%), phenolic compounds (13%) and maximum quantum efficiency (17%) in dark condition and in light condition. Application of 24-Epibrassinolide resulted in a significant increase of chlorophyll a and total chlorophyll, carotenoids, phenol content, maximum quantum efficiency in the dark condition and photochemical quenching of fluorescence. The highest chlorophyll content and carotenoids were observed in treated plants with 0.1 µM 24-Epibrassinolide, while the maximum phenol content was obtained by application of 0.01 µM 24-Epibrassinolide. The application of methyl jasmonate significantly affected the major chlorophyll and accessory pigments (except phenol) of fennel. Plants treated with 50 µM methyl jasmonate exhibited higher concentrations of chlorophyll a (3.25 mg per g FW-1), total chlorophyll (4.35 mg per g FW-1), carotenoids (0.87 mg per g FW-1) and flavonoids (4.75 µg per g FW-1). A significant dry weight increased after the application of methyl jasmonate and it can be concluded that the most effective treatment in this regard for fennel plants was 50 µM methyl jasmonate.