THE EFFECTS OF EXOGENOUS MELATONIN APPLICATION ON GROWTH RATE PARAMETERS AND BIOACTIVE COMPOUNDS OF SOME SPINACH CULTIVARS (SPINACIA OLERACEA L.) GROWN UNDER WINTER CONDITIONS

. The present study was carried out in order to reveal the effects of exogen melatonin (50MT: 50 µM - 100 MT: 100 µM) treatment on the growth rate characteristic and bioactive compound content variations of three spinach cultivars (Acosta-ACO; Anlani-ANL, and Matador-MTR, respectively) grown under cold conditions. While MTR was the richest variety in terms of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content, ANL was the richest variety in terms of Chl a to Chl b ratio, and xanthophyll content. Ascorbic acid and protein concentration were stimulated by MT in all three variants, but ANL had the highest value. While the proline content of cultivars decreased with only 50 MT in ACO when compared to the control, GB content decreased in MT doses. RWC increased with MT in ANL, whereas it caused to a decrease in RWC of 100 MT in ACO and 50 MT in MTR. MDA concentration was at a lower level and decreased only in ACO with 50 MT when compared to the control, while the H 2 O 2 concentration was higher at MT doses in all three species. MT treatment stimulated SOD activity in ACO and ANL and increased POD activity in all three variants. Considering the growth characteristics such as root/stem length, leaf characteristics, and biomass, exogenous MT doses had positive effects on all three cultivars. These findings suggest that foliar MT treatment can attenuate cold damage by enhancing the enzymatic and non-enzymatic antioxidant capacity of spinach seedlings, as well as the growth rate.