Document Type : Full Paper
Authors
1 Department of Horticultural Sciences, Faculty of Agriculture, Lorestan University, Khorramabad, Iran.
2 Department of Horticultural Sciences, Faculty of Agriculture, Lorestan University, Khorramabad, Iran
Abstract
Keywords
Main Subjects
Extended Abstract
Introduction
The use of modifiers in drought stress conditions is an optimal and low cost strategy, therefore understanding the different characteristics of the plant in these conditions leads to achieve appropriate production management methods. Drought stress reduces the size and increases the density of leaf stomata, also causes a decrease in stomatal conductivity. In addition to defense systems, which exist in the plant itself, there are other methods to increase the resistance of plants in deficit water stress condition, such as the use of plant growth regulators. Salicylic acid is a phenolic compound and a natural hormone, which is known as one of the common compounds, to decrease the harmful effects of environmental stresses. The purpose of this research was to investigate the physiological and developmental responses as well as the activity of some enzymes of physalis to deficit water and explore the role of salicylic acid in improving the negative effects of water stress.
Materials and Methods
This research was conducted in 2017 in the research greenhouse of Lorestan University, Faculty of Agriculture, located in Khorramabad city, as a factorial experiment based on a completely randomized design. The greenhouse is located at 48 °22 ´E and 33 °29 ´N and at 1125 meters above the sea level. The relative humidity of the greenhouse was 60-90%, the light intensity 600 µmol/m2/s, the day temperature of the greenhouse 28-30 C° and the night 22-24 C°. The plants were planted at the end of May and two weeks after transplanting were irrigated in 3 levels of field capacity including 95% (control), 85% and 75%. Salicylic acid was applied in four concentrations (0, 0.5, 1 and 2 mM), one week before applying the drought stress. Foliar spraying was done every 10 days. In order to apply drought stress and control the soil moisture, the FC and Permanent Wilting Point were determined using a pressure plate device. All the pots were irrigated in the same way until the 4-leaf stage, when the irrigation treatments were applied.
Results
The results showed that deficit water stress reduced relative water content (RWC), gas exchanges, and changes in stomatal aperture of the plant. Deficit water stress also affected the activity of antioxidant enzymes, the amount of electrolyte leakage and MDA; caused the amounts of these characteristics to increase. Salicylic acid application in this study, reduced the negative effects of water stress. According to the obtained results, in deficit water stress conditions, the length and width of the stomatal guard cells decreased and the stomata density enhanced. Stomatal conductivity, transpiration, carbon dioxide beneath the stomatal chamber (INT Co2), and photosynthesis rate demonstrated a decreasing trend at 85% and 75% field capacity. The highest photosynthesis rate was due to foliar application of salicylic acid at concentration of 1 and 2 mM. Hence, for the cultivation of physalis in arid and semi-arid regions, irrigation levels of 95% and 85% of the field capacity, along with the application of salicylic acid in concentrations of 1 and 2 mM, can be suggested, while the irrigation level of 75% FC is not recommended, due to the negative effect on the measured parameters.
Discussion
With the decrease in the level of irrigation, the rate of photosynthesis decreases drastically due to the decrease in chlorophyll production and the increase in its decomposition. Salicylic acid increases the rate of photosynthesis and dry matter of the plant by increasing the leaf surface, chlorophyll content, and preventing the ethylene production. Water stress causes the stomatal cells to close and the concentration of carbon dioxide in the leaf mesophyll tissue decreases, consequently NADPH accumulates in the chloroplast. In this case, the amount of available NADP+ to carry out photoreactions reduces and oxygen acts as an electron acceptor. This process leads to the production of superoxide radicals and other reactive oxygen species, which will eventually result in oxidative stress. By changing the activity of catalase, peroxidase and ascorbate peroxidase enzymes, and other enzymes involved in the decomposition of hydrogen peroxide, salicylic acid causes a slight increase in the amount of hydrogen peroxide as a secondary messenger that induces resistance and antioxidant capacity. To induce resistance, only a small amount of hydrogen peroxide is needed, because higher amounts will be a factor in creating oxidative stress.
Conclusion
According to the results, with the reduction of irrigation level and FC, physalis showed a negative reaction to the stress by increasing the activity of antioxidant enzymes and changing stomatal aperture. The use of salicylic acid in water stress conditions improved the studied characteristics compared to the control. Considering the non-significant effects of 95% FC and control irrigation levels and also improving effect of salicylic acid on most studied traits, irrigation levels of 95% and 85% of the field capacity along with the application of salicylic acid in concentrations of 1 and 2 mM can be suggested. Although salicylic acid reduced the effects of stress at the irrigation level of 75%, but this level of irrigation is not recommended due to the negative effects on the measured parameters.
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