عنوان مقاله [English]
Introduction: Salinity tolerance in plants can increase the importance of it as a result of the decreasing availability of high-quality irrigation water. Saline irrigation water can have many negative effects on crops. When irrigation water has high salinity, the salt may precipitate on the leaves as the water evaporates. Thus it can result in foliar uptake and phytotoxicity. The irrigation water may also cause accumulation of salt in the substrate, which may lead to salt uptake by the plants. Salt injury occurs when too much NaCl accumulates in the substrate. When excessive concentrations of NaCl are present in the soil, water uptake may be inhibited and it causing a physiological drought stress. However, potassium is required by plants in amounts (in kg unit) of similar or greater than nitrogen (N). K Uptake by the plant is highly selective and closely coupled to metabolic activity. At all levels in plants, within individual cells, tissues and in long-distance transport via the xylem and phloem, K exists as a free ion in solution or electrostatically bound cation. Potassium takes part in many essential processes such as enzyme activation, protein synthesis, photosynthesis, phloem transport, osmoregulation, cation-anion balance, stomatal movement and light-driven nastic movements. Potassium Chloride (KCl) is used as a source of nutrients in agricultural development and also used as relieve salinity stress.
Materials and Methods: In order to study the mitigation effects of KCl on salinity (NaCl) in mustard plant (Parkland and Goldrush), an experiment was carried out at the Research Greenhouse, Faculty of Agriculture, Ferdowsi University of Mashhad, Iran. The experiment was managed as a factorial arrangement based on completely randomized design in three replications. Treatments were included NaCl (0, 30, 60 and 90 mM) and KCl (0 and 20 mM) and two cultivars.
Relative water content was calculated by the following formula using leaf disc obtained from a young leaf of each plant.
(DW+ FW/ DW+ TW)*100FW=fresh weight, DW=dry weight, and TW=turgid weight
Electrolytic leakage was calculated by the following formula:
EL=L1/L2 where L1 is electric conduction of leaf after putting in the deionized water in 25°C and L2 is the electric conduction of the autoclaved samples.
Leaf area was measured by Leaf area meter. Shoot and root dry weights were determined after drying the samples in 75°C for 48 h.
Chlorophyll concentration was calculated by the fallowing formula:
Chla (μg/ml) = 15.65A666 – 7.340 A653
Chlb (μg/mml) = 27.05A653 – 11.21 A666
Analysis of variance was calculated using MSTAT-C.1software and means were compared by LSD test at probability level of 5%.
Results and Discussion: The results showed that the treatments of NaCl, KCl and interactions with cultivars were significantly different on dry weight, leaf area, photosynthesis, stoma conductivity and chlorophyll rate. The maximum shoot dry weight (3.44 g/plant) and photosynthesis rate was obtained from T2 (20 mMKCl and without NaCl). The maximum membrane stability index was obtained in Goldrush cultivar and T2. The minimum of these traits were observed in zero mMKCl and 90 mMNaCl. High level of NaCl (60 and 90 Mm) and increasing application of KCl could not improve all traits. According to the result of the analysis of variance increasing density of sodium chloride in planting areas has a special effect on the size of leaves, weight of dried plant and each leaf and dried root. This effect shows a meaningful variation between the weight of dried leaves and its dried root and shoots. The salty areas have a lot of negative ions like Magnesium, Chlorine, sodium and sulfate. These materials are harmful by themselves or cause affective disorder in plants metabolism. Salinity treatments applied to significant influence (p≤0.01) on the characteristics of photosynthesis, stomatal conductance and number of stomata was read out by SPAD. For example, sodium and potassium competition and chlorine and nitrate competition impairs the absorption of nutrients. The result of this reaction is that the plant needs more energy for producing organic matter so it loses most of its energy to resist against salt. This situation causes a low activity of the root and the growing of shoot consequently reduces. Also, weight and length of plant would reduce too. For example, existing potassium in salty lands causes the reduction of sodium in the shoot of plants. This research was done in a pot with the same amount of salt. Potassium causes the reduction of toxicity effects of sodium. This research showed that the potassium can regulate osmotic pressure and permeability of plant cell membranes and also cause to increase plant tolerance to salinity.
Conclusion: In salty condition, increasing the amount of sodium causes the reduction of potassium, compared with sodium. As a matter of fact this kind of reaction causes the reduction of potassium compared with sodium. We know that potassium can cause a suitable osmotic pressure and reduce the destructive effect of oxidation. So, amount of potassium more than sodium in salty lands is known as the standard resistance. In general, increasing the salinity of sodium chloride can decrease morphological and physiological traits of mustard. The use of potassium chloride in T2 treatment showed the best result. However, Goldrush cultivar showed better results compared with Parkland cultivar in salt tolerance.