Exogenous melatonin improves pear resistance to Botryosphaeria dothidea by increasing autophagic activity and sugar/organic acid levels

Pear is a perennial deciduous fruit tree of the Rosaceae Pyrus genus, and is one of the main fruit trees worldwide. The pathogen Botryosphaeria dothidea infects pear trees and causes pear ring rot disease. According to our research, exogenous melatonin application enhanced resistance to B. dothidea in pear fruit. Melatonin treatment of pears significantly reduced the diameter of disease spots and enhanced the endogenous melatonin content under B. dothidea inoculation. Compared with H2O treatment, melatonin treatment suppressed the increase in ROS and activated ROS-scavenging enzymes. Treatment with exogenous melatonin maintained AsA-GSH at more reductive status. The expression levels of core autophagic genes and autophagosome formation were elevated by melatonin treatment in pear fruit. The silencing of PbrATG5 in Pyrus pyrifolia conferred sensitivity to inoculation, which was only slightly recovered by melatonin treatment. After inoculation with B. dothidea, exogenous melatonin treatment increased the contents of soluble sugars and organic acids in pear fruits compared with H2O treatment. Our results demonstrated that melatonin enhanced resistance to B. dothidea by increasing the autophagic activity and soluble sugar/organic acid accumulation.

Melatonin increases growth and salt tolerance of Limonium bicolor by improving photosynthetic and antioxidant capacity

Background Soil salinization is becoming an increasingly serious problem worldwide, resulting in cultivated land loss and desertification, as well as having a serious impact on agriculture and the economy. The indoleamine melatonin (N-acetyl-5-methoxytryptamine) has a wide array of biological roles in plants, including acting as an auxin analog and an antioxidant. Previous studies have shown that exogenous melatonin application alleviates the salt-induced growth inhibition in non-halophyte plants; however, to our knowledge, melatonin effects have not been examined on halophytes, and it is unclear whether melatonin provides similar protection to salt-exposed halophytic plants. Results We exposed the halophyte Limonium bicolor to salt stress (300 mM) and concomitantly treated the plants with 5 μM melatonin to examine the effect of melatonin on salt tolerance. Exogenous melatonin treatment promoted the growth of L. bicolor under salt stress, as reflected by increasing its fresh weight and leaf area. This increased growth was caused by an increase in net photosynthetic rate and water use efficiency. Treatment of salt-stressed L. bicolor seedlings with 5 μM melatonin also enhanced the activities of antioxidants (superoxide dismutase [SOD], peroxidase [POD], catalase [CAT], and ascorbate peroxidase [APX]), while significantly decreasing the contents of hydrogen peroxide (H2O2), superoxide anion (O2•−), and malondialdehyde (MDA). To screen for L. bicolor genes involved in the above physiological processes, high-throughput RNA sequencing was conducted. A gene ontology enrichment analysis indicated that genes related to photosynthesis, reactive oxygen species scavenging, the auxin-dependent signaling pathway and mitogen-activated protein kinase (MAPK) were highly expressed under melatonin treatment. These data indicated that melatonin improved photosynthesis, decreased reactive oxygen species (ROS) and activated MAPK-mediated antioxidant responses, triggering a downstream MAPK cascade that upregulated the expression of antioxidant-related genes. Thus, melatonin improves the salt tolerance of L. bicolor by increasing photosynthesis and improving cellular redox homeostasis under salt stress. Conclusions Our results showed that melatonin can upregulate the expression of genes related to photosynthesis, reactive oxygen species scavenging and mitogen-activated protein kinase (MAPK) of L. bicolor under salt stress, which can improve photosynthesis and antioxidant enzyme activities. Thus melatonin can promote the growth of the species and maintain the homeostasis of reactive oxygen species to alleviate salt stress.

Role of Exogenous Melatonin, Hydrogen Sulfide and Nitric Oxide on Organic Acid Content of Eruca sativa L. under Salt Stress

Salt stress affects agricultural output by influencing numerous internal metabolisms in plants and disrupting physiological and biochemical activities such as photosynthesis, translocation, respiration, and growth stimulants. The role of exogenous melatonin, hydrogen sulfide and nitric oxide application on the organic acid contents of rocket plants under salt stress was examined in this study. Different salt doses (0, 150 and 250 mM NaCl) and exogenous applications (0, 50 and100 µM) were made to rocket plants under the greenhouse conditions. Plants leaves and roots exhibited a decline in the organic acid contents under salinity stress. Application of the amendments, however, was found significant in mitigating the negative effect of salt stress. Melatonin and hydrogen sulfide treatments had a stronger anti-salt action in the leaves. On the other hand, nitrous oxide role was more obvious in the roots followed by melatonin. With this, exogenous applications to the plant mitigated the harmful effects of salt stress on organic acid contents depending on the dose.

FIBRINOLYTIC ACTIVITY IN HEART TISSUE IN HYPOTHYROID AND HYPERTHYROID RATS UNDER THE INFLUENCE OF EXOGENOUS MELATONIN AND BLINDING CONDITIONS (ENUCLEATION)

The aim of our scientific work was to study the effect of exogenous melatonin on the indicators of fibrinolytic processes in the heart tissues and to analyze the changes in fibrinolytic activity occurring in the heart tissues of enucleated hyper- and hypothyroid white rats. The experiments were carried out on white nonlinear male rats weighing 0.12-0.14 kg. 4 experimental groups of animals were formed. The control group consisted of 11 normothyroid rats, which were injected with a melatonin solution in appropriate volumes. The animals were euthanized under light ether anesthesia. Samples of the examined heart tissue were ground in a glass homogenizer with borate buffer (pH 9.0). The homogenate was used in biochemical analysis. Determination of the total, enzymatic and non-enzymatic fibrinolytic activity (TFA, EFA, NFA, respectively) in the heart tissues was carried out by the method of azofibrin lysis (LLC "Simko", Ukraine). Statistical processing of the results was carried out by the method of variation statistics using the Student's test. Experimental studies on nonlinear male white rats have shown that the introduction of exogenous melatonin, as well as modeling the conditions of endogenous melatonin overproduction by blinding (enucleation) cause an increase in the intensity of enzymatic and non-enzymatic fibrinolysis in heart tissue in normotyroid animals. At other hand, enucleation causes an increase in the intensity of fibrinolysis in the tissues of the heart in hypothyroid rats, but not in hyperthyroid.