Shadab panahi

The effect of melatonin application on the physiology and growth of sweet pepper (Capsicum annuum L.) under salt stress

Bell pepper is one of the most important vegetables in the world, with special significance in economy and food. Moreover, a great part of problem in the function and growth of plants could be attributed to environmental stresses, including salinity. Salinity happens as a result of lack of fresh and high-quality water as far as watering the plants is concerned. Salinity in water and soil can cause different morphological, physiological, molecular and biochemical changes in plants. In addition, resistance of salinity is an unchangeable characteristic of every plant species, though it might change in different levels of growth. The present research was carried out to investigate the physiological traits of two cultivars of bell pepper, namely green bell pepper and orange bell pepper; the aim was to investigate the expression of psy gene under salinity as a treatment. This research was conducted in the greenhouse of Isfahan University of Technology, Isfahan, Iran, in summer 2019. To this end, it was designed in the form of factorial experiments, which were completely random, where the first factor included four levels of salinity (watering with normal water, watering with salty water with values of 1.5, 4.5, and 6.5 deci seimens/meter of NaCl) and the second factor included two bell pepper cultivars. The indexes measured in the experiments comprised of expression of psy gene, the consideration of physio-chemical traits such as the amount of chlorophyll, the content of sugar and starch, the amounts of Na, Cl and K in stem and root, the amounts of Proline, transpiration, porous conductance, photosynthesis and the evaluation of changes of Abscisic acid. At the time of salinity stresses, carotenoids acted as the prerequisite for the production of the hormone Abscisic acid; also, psy gene was required for the production of ABA. Five hours after the implementation of the salinity stress, samples were separated from the roots and RNA was extracted. Then, cDNA synthesis was performed so that changes of gene expression would be evaluated in Real-time PCR reaction. To perform Real-time PCR, firstly specific primers were combined from the sequences in the NCBI database and then the initiator design was performed based on the protected areas. It was shown that gene expression was increased by increasing the level of salinity, followed by an increase in the rates of abscisic acid. In addition, results of physiological indexes revealed that increasing the level of salinity increased the rate of ascorbate peroxidase enzymes in orange bell pepper and that the maximum rate of this enzyme was observed for the 6.5 deci seimens/meter treatment of orange cultivar. In all levels of salinity, green bell pepper produced more starch than the amount produced by orange bell pepper and the highest amount of sugar and starch were observed for 6.5 deci seimens/meter treatment in the green cultivar. Moreover, increasing the level of salinity led to increases in the amounts of K in root and stem and the amount of NA in stem, as compared with the control. Furthermore, 6.5 deci seimens/meter treatment had the highest amounts of Na and K in root and stem, as compared with the control. As the levels of salinity, consideration of the content of Proline and the amount of Phenol were significant, with increasing trends. Also, increasing the level of salinity led to significant reduction of indexes such as the amount of transpiration, porous conductance and the carbon dioxide under the pores; however, increasing the level of salinity did have any significant effect on the amount of Chlorophyll, as compared to the control.