Journal of Plant Process and Function

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Tuberose flower is one of the aromatic bulbous flowers in tropical and subtropical regions. In order to study the effects of exogenous melatonin (M) on some physiological parameters of cut flower Tuberose, an experiment was performed base on a completely randomized design(CRD) with three replicates and 15 flower per replication. Melatonin (in concentrations of 0 and 250 μL.L-1 for 4 hours) was used as pulse-treatment. Melatonin treatment compared to the control prevented the decrease of Relative water content (RWC), the increase of Electrolyte leakage (EL), and malondialdehyde (MDA) concentrations in the tissues (leaves and petals). In addition, melatonin increased the amount of ascorbate peroxidase (APX) and peroxidase (POD) activities in the 6th day of storage compared to 3rd and 0th days. Peroxidase activity decreased in control treatment on 3rd and 6th days, respectively. While the activity of this enzyme was increased in melatonin treatment. The catalase (CAT) activity content of the tissues (leaves and petals) increased on 3rd day of storage and decreased on the 6th day. Therefore, it seems melatonin may help reduce oxidative stress and the lipids peroxidation and delays process of senescence in Tuberose flower.

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Melatonin plays important and different roles in many aspects of plant growth and development. Recently it has been shown that melatonin has antioxidant properties and plays in processes of germination, maturation, senescence, cytoprotection, resistance to biotic and abiotic stress and etc. However, its role in post-harvest processes and water relations cut flowers has not yet been determined. In this study, the effects of different concentrations of melatonin on five levels (0, 50, 100, 250 and 500 µM) and three times (2, 4 and 6 hours) on the cut tuberose cv. Pearl were investigated as pulse treatments. cut flowers were then transferred to distilled water and evaluated daily for vase life and water relations. However, pulse treatments for 4 h with 250 µM melatonin solutions extended vase life and suppressed a reduction in fresh weight during the post-harvest period. The amounts of water uptake and water loss by the cut flowers decreased upon melatonin treatment. The results showed that melatonin treatment resulted in prolonged vase life, increasing the number of opened florets in the inflorescence, reducing water loss and maintaining the water balance in cut tuberose. Treatment of 250 µM melatonin resulted in a 1.5-fold increase in vase life of cut tuberose compared to control treatment. The highest water uptake and water loss were observed in control treatment and the lowest water uptake and water loss were observed in treatment with 500 µM melatonin. As the melatonin concentration increased, endogenous melatonin levels increased. Melatonin application caused a positive change in chlorophyll and carotenoid levels. The role of melatonin at high concentrations (500 µM) may be similar to the abscisic acid in stomata closure and reduced transpiration, or at concentrations of 100 and 250 µM melatonin, possibly maintaining cells membrane integrity, may cause turgidity of cells

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In order to evaluate the reaction of the peppermint plant (Mentha piperita L.) to water deficit stress and the use of growth-promoting bacteria, a factorial experiment was conducted in the form of a completely randomized design with four replications in the research greenhouses of the Faculty of Agriculture of Lorestan University in 2022. The first factor included water deficit stress (80, 50, and 20% available water content (AWC)), and the second factor included growth-promoting bacteria (without the use of bacteria (control), Pseudomonas putida strain, and Curtobacterium sp. strain wlu). The results of the present experiment show the water deficit stress had a significant effect on the morphophysiological and biochemical indicators, so that at the level of 20% AWC, it increased electrolyte leakage (219%), malondialdehyde concentration (50%) and the activity of antioxidant enzymes such as catalase (1174%), peroxidase (308%) and ascorbate peroxidase (82.7%) compared to the control treatment, but growth components such as plant height, stem number, total fresh and dry weight (29.3%, 37.2%, 56.1% and 55.5%, respectively), relative leaf water content (36.1%), essential oil percentage and yield (38.8% and 71.6%, respectively) decreased compared to the control treatment. Photosynthesis rate, intracellular carbon dioxide concentration, stomatal conductance, and mesophyllic conductance also decreased by 76.5%, 61.8%, 40%, and 38.5%, respectively, under water deficit stress conditions of 20% AWC. The application of growth-promoting bacteria in stress and non-stress conditions improved the growth components by increasing water absorption through root growth, increasing the activity of antioxidant enzymes, and increasing the rate of photosynthesis and stomatal conductance. Also, the percentage of essential oil and the yield of essential oil increased under the influence of the use of growth-promoting bacteria. In general, the results showed that the treatment of growth-promoting bacteria, especially the Pseudomonas putida strain, improved the water balance through increasing water absorption, increased biomass due to increasing the rate of photosynthesis, and also increased the activity of antioxidant enzymes to reduce the negative effects of water deficit stress in peppermint.