Özet:

Today, drought stress threatens the world seriously. Determining the effects of some exogenous stimulators in acquiring resistance against stress will contribute to agriculture under drought stress. In this regard, we investigated the effects of melatonin (MEL) on Morus nigra cv. 'Eksi Kara' (black mulberry) in challenging drought. To reach this object, we reproduced 'Eksi Kara', which is registered in Turkey and has economic importance, in tissue culture by using the meristem culture method. Plants were then transferred in a medium containing polyethylene glycol (PEG) 8000, which causes -1.5 MPa drought stress, and 20 μl MEL has applied. Leaf samples were taken on the 5th, 10th, and 15th days after treatments in groups of plants grown in a different medium (Control, Control+MEL, PEG and PEG+MEL). The changes in the pigment system, relative water content (RWC) and antioxidant system were evaluated comparatively between the groups to assess plants' growth and determine their roles in coping with stress. Our findings showed that RWC decreased in leaves under drought. Exogenous MEL added in MS medium had a mitigation effect on stress. The reduction was detected in the chlorophyll and carotenoid content of leaves. Moreover, MEL+PEG combination improved the chlorophyll level. It was seen that exogenous MEL application promoted the plant defence mechanism of M. nigra plants, which exposed to drought stress, by increasing the accumulation of non-enzymatic antioxidants; total glutathione (GSH), total phenolic, proline) and activities of antioxidant enzymes; catalase (CAT), superoxide dismutase (SOD), Glutathione-S-transferase (GST), glutathione reductase (GR), peroxidase (POD), ascorbate peroxidase (APX). This study also indicates that the application of MEL+PEG composition partially prevented membrane lipid peroxidation by decreasing (malondialdehyde) MDA content.

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