Effects of Exogenous Melatonin on Chrysanthemum Physiological Characteristics and Photosynthesis under Drought Stress

Abstract

Melatonin has been confirmed to relieve drought stress in various plant species. However, the mechanism in garden chrysanthemums remains to be elucidated. Here, we examined the putative role of exogenous melatonin application in improving drought-stress tolerance in Chrysanthemum seedlings. Treatment with melatonin (100 µM) significantly mitigated the negative effects of drought stress on the seedling photosynthetic parameters and physiological and biochemical indexes. The increased tolerance conferred by exogenous melatonin was attributable to increased photosynthetic activity, which alleviates drought-induced oxidative damage by reducing malondialdehyde accumulation. In other words, the combined application of MT and PEG was better than their individual applications, as it prevented heat-induced membrane damages by declining the hydrogen peroxide (28%), malondialdehyde contents (38%), and relative electrical conductivity (19%) as compared to PEG. Interestingly, the melatonin application stimulated the activity of major antioxidant enzymes such as superoxide dismutase (21%), catalase (26%) and polyphenol oxidase (35%). In addition, exogenous melatonin promoted photosynthesis. Compared with the PEG drought-stress treatment, the melatonin treatment significantly increased the net photosynthetic rate (39%), stomatal conductance (27%), and transpiration rates (18%), while decreasing the intercellular CO2 concentration (10%). The photochemical quenching coefficient (46%), photosystem II (PSII) maximum photochemical quantum yield (22%), apparent electron transfer rate (37%), and PSII potential photochemical efficiency (18%) showed an upward trend. In summary, exogenous spraying of MT can effectively improve drought tolerance and mitigate the damage caused by drought stress in the “Xuanqiu ninghong” Chrysanthemum.

Melatonin imparts tolerance to combined drought and high-temperature stresses in tomato through osmotic adjustment and ABA accumulation

“…As a result, melatonin-sprayed plants showed an increase in F v /F m , relative water content, and chlorophyll content compared with plants without melatonin spray. Similar findings have been reported in studies conducted on chrysanthemum ( Luo et al., 2023 ) and strawberry ( Manafi et al., 2021 ).…”

Melatonin Mitigates Water Deficit Stress in Cenchrus alopecuroides (L.) Thunb through Up-Regulating Gene Expression Related to the Photosynthetic Rate, Flavonoid Synthesis, and the Assimilatory Sulfate Reduction Pathway

“…Luteolin and its derivatives exhibit exceptional properties in scavenging ROS and protecting cells during water deficit stress [ 44 ]. This experiment combined with previous studies suggested that melatonin may enhance the antioxidant capacity of plants by regulating DEGs in the phenylpropanoid and flavonoid synthesis pathways [ 39 , 43 , 45 , 46 , 47 ]. However, these results need to be further confirmed by rigorous field trials.…”

Impact of Exogenous Melatonin Application on Photosynthetic Machinery under Abiotic Stress Conditions

“…Melatonin treatment through foliar and root irrigation in soybean resulted in a slight increase in chlorophyll levels and a reduction in ABA content compared with control plants, indicating improved drought resistance [ 72 ]. Furthermore, in Chrysanthemum seedlings, exogenous application lessened the impact of drought stress on the photosynthetic mechanism, promoted seedling growth, reduced water loss, preserved chlorophyll levels, increased soluble protein and sugar levels, and enhanced antioxidant enzyme activity, leading to improved drought tolerance [ 73 ]. Finally, foliar treatment on Moringa oleifera enhanced photosynthetic pigment constituents, and the accumulation of IAA and phenolics, resulting in increased photosynthesis [ 74 ].…”