Salinity is one of the most important plant stresses which affects growth of the plant. 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, with the aim of considering the behavior of psy gene under salinity as a treatment. This research was performed in the form of factorial experiments, which were completely random, where factors 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 two bell pepper cultivars. 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. Therefore, sampling was conducted 5 hours after the implementation of the salinity stress and then RNA was extracted. After the confirmation of the quality and quantity of the extracted RNA, cDNA synthesis was performed so that changes of the expression of gene would be evaluated in Real-time PCR reaction. To perform Real-time PCR, first a specific primer was combined from the sequences in the NCBI database, using the MEGA 4.0 software; then the initiator design was performed based on the protected areas. It was shown that that increasing expression of gene was increased by increasing the level of salinity, followed by an increase in the rates of abscisic acid and the carotenoids. In addition, it was revealed that increasing levels of salinity increased the rate of ascorbate peroxidase enzymes in orange bell pepper and that the maximum rate of this enzyme was dedicated to treatment. General findings indicated that, at 5% of significance level, the variability and salinity levels were significant in chlorophyll b and the total chlorophyll, respectively. In all levels of salinity, green bell pepper produced more starch than that produced by the orange bell pepper and the highest and starch were observed in treatment with 6.5 deci seimens/meter. Moreover, increasing level of salinity led to increase in Na and Cl elements. At 5% of significance level, these elements were significant in proline and phenol with an increasing upward trend. In addition, the effect of salinity levels on weights of both the dry and wet were not significant. Level of salinity led to significant effect on variables such as photosynthesis, trairation, porous conductance and the carbon dioxide under the pores; also, it had no significant effect on the chlorophyll. Keywords: Bell pepper, psy gene, Carotenoids, Abscisic acid.
