بهبود شاخص‌های رشد گیاه پپرومیا هندوانه‌ای (Peperomia argyreia) با افزودن غلظت‌های مختلف سیلیکات پتاسیم و تنظیم‌کننده‌های هورمونی در شرایط کشت درون‌شیشه‌ای

Introduction
Silicon is one of the most abundant mineral elements in the soil, which is widely used in various biological and non-biological fields. Due to its positive effect on the growth of plants and their tolerance to various stresses, this element has received attention in recent years in the production of plants in field cultivation and in vitro culture. One of the most famous silicates in the plant field research is potassium silicate. The present study was designed to investigate the effect of different concentrations of potassium silicate and plant growth regulators on the growth and direct regeneration parameters of watermelon Pepromia plant under in vitro culture conditions.
 
Materials and Methods
The leaf parts of one-year-old Peperomia argyreia mother plant were cultured after disinfection on MS culture medium containing 1 mgl^-1 of Benzyladenine (BA) and 0.5 mgl^-1 of Naphthalene acetic acid (NAA). Three months after cultivation, the regenerated shoots were cultivated in MS culture medium containing 0.5 mgl^-1 of IBA for rooting to produce sterile seedlings. In order to conduct the experiment, nodule explants from in vitro grown seedlings cultured on MS culture medium containing potassium silicate at three levels of zero, 100 and 1000 micromolar along with different concentrations of plant growth regulators BA and NAA at three levels of zero, 1 mgl^-1 BA + 0.5 mgl^-1  NAA and 3 mgl^-1  BA + 1.5 mgl^-1 NAA and the culture dishes were placed in the growth chamber under lighting conditions of 16/8 light/ dark provided by fluorescent lamps with light intensity of 100 μmol m⁻² s ⁻¹ and temperature of  24°C. Three months after applying the appropriate treatment and regeneration of the plants, the morphological and physiological indicators of the plants such as the number of stems, the number of leaves, the number of nodes, the height of the stem, the fresh weight and the dry weight of the plant and the amount of photosynthetic pigments were evaluated.
The experiment was conducted as a factorial in a completely randomized design. The factors included potassium silicate at three levels and different concentrations of plant growth regulators at three levels. Each treatment had three replicates and four explants in each replicate. The data obtained from the examination of each experiment was analyzed using the statistical software Infostat and the comparison of the average data was done by the LSD test. EXCEL software was used to draw graphs and record each data.
 
Results and Discussion
The highest rate of shoot regeneration was observed in all culture media containing plant growth regulators at the rate of 1 mgl^-1 BA + 0.5 mgl^-1 NAA. However, the addition of 100 and 1000 micromolar potassium silicate caused a significant increase in the number of regenerated shoots. The height of regenerated shoots in media with plant growth regulators was not affected by potassium silicate, however, the addition of potassium silicate to the MS culture medium without growth regulators had a significant effect on the height of regenerated stems, in such a way that the addition of 1000 micromolar potassium silicate to the MS culture medium resulted in the growth of regenerated shoots about 4 times. The highest number of nodes was also found in the regenerated shoots cultivated in the culture medium containing 100 micromolar potassium silicate along with plant growth regulators at the rate of 1 mgl^-1 BA + 0.5 mgl^-1 NAA with an average number of 7 nodes. Although the plants in the MS culture medium had a high amount of photosynthetic pigments, the increasing effect of potassium silicate cannot be ignored. It should be noted that the highest amount of fresh weight was observed in the regenerated plants cultivated in the culture medium containing 1000 micromolar potassium silicate along with plant growth regulators at the rate of 1 mgl^-1 BA + 5/ 0 mgl^-1 NAA and 100 µM potassium silicate along with plant growth regulators at the rate of 3 mgl^-1 BA + 1.5 mgl^-1 NAA with an average weight of 0.33 grams.
 
Conclusion
In sum, the results of the present study showed that the use of potassium silicate in the culture medium of Pepromia plant has a positive effect on the regeneration and in vitro growth of this plant.