Introduction
In recent years, the application of nanoparticles has been used successfully in plant tissue culture, which has a tremendous impact on the removal of microbial contamination of the explant through the use of these materials and also the positive role of these materials in callus formation, organogenesis, somatic embryogenesis, somaclonal variation and production of secondary metabolites. Proline is a proteogenic amino acid that accumulates as a useful solvent in plants under both stress and non-stress conditions. Recent discoveries indicate that proline plays an important role in plant growth and differentiation throughout the life cycle. Chitosan was found to enhance secondary metabolite production in cell suspensions and calli of various species applied in micropropagation, chitosan could improve plantlet quality in vitro, in consequence facilitating the subsequent acclimatization of plantlets to ex vitro conditions. The aim of this work was to investigate whether the in vitro application of nanocomposite and moderate salinity can improve microtuberization.
 Materials and Methods
After the cultivation, the jars containing the explants were transferred to the growth chamber under absolute darkness and at a temperature of 18±2°C. The cultures were kept in these conditions for 4 months without sub culturing the samples for this purpose. MS medium containing 80 g of sucrose, containing proline at concentrations of 20 and 40 mg L^-1, chitosan at a concentration of 240 mg L^-1, proline 20 and chitosan 240 mg L^-1, proline 40 and chitosan 240 mg L^-1, 120 mg L^-1, proline nanocomposite coated with chitosan 120 and 240 mg L^-1 and control treatment, as well as non-salinity treatments with the same compounds and concentrations mentioned for salinity were cultured. Factorial experiment was conducted base on a completely randomized design with three replications on single nude explants of mentioned cultivar.
 Results and Discussion
The results of this study show that moderate salinity has a significant effect on the first, second, third and last month of microtuberization. (in 1% level). The results of the comparison of mean microtuber yield showed that the highest yield was obtained when 240 mg of chitosan was treated with 20 mg / l of proline at moderate salinity with an average weight of 210 mg. Moreover, a concentration of 20 mg / l proline alone in moderate salinity was not sufficient to stimulate microtubers., but a concentration of 40 mg L^-1 proline in mild salinity was satisfactory. According to the results of this study, it can be suggested that the use of chitosan compounds with proline and the use proline nanocomposite coated with chitosan with moderate salinity can be used to produce suitable microtuberization in the in vitro conditions of potatoes. In order to prove our results with the results of previous researchers, the results of chitosan application experiment on the growth and yield of miniature showed that application of 500 mg L^-1 chitosan produced minituber weighing more than 1.5 g per seedling. Chitosan increased other traits including number of minituber per seedling, number of leaves per seedling and seedling length (Asghari-Zakaria et al., 2009). In the study of the effect of cobalt nanoparticles on the morphological characteristics of Santana cultivar in vitro, it was observed that the presence of cobalt nanoparticles caused the formation of microtubers faster, also the maximum size and function of microtubers from the combination of 2.5 mg. Cobalt nanoparticles with 80 g L^-1 sucrose were obtained (Hamza, 2019).
Conclusions
In this experiment, proline nanocomposite coated with chitosan was successfully synthesized and according to the obtained results, it can be used in plant tissue culture and in vitro microtuberization. In the field of potato microtuberization, the use of nanocomposite showed a significant increase in the number of microtubers compared to the control, which showed a significant effect in the late stages of microtuberization. Also, the use of moderate salinity with treatment nanocomposite is effective for stimulating microtuberization, which increases microtubers yield. Based on the results of this experiment, a concentration of 120 mg L^-1 proline nanocomposite coated with chitosan is a more suitable concentration for potato microtuberization.