*6.1.5 Ion toxicity*

Salt stress occurs due to accumulation of high amounts of Cl<sup>−</sup> or Na+ ions in soil and causes ion toxicity in plant. Although plant responses against salinity varies from species to species, generally excessive intake of Na+ causes nutrient imbalance [51–57]. Na+ ion has toxic concentration earlier than Cl− ion [4]. While high concentrations of Na+ ions cause negative effects in photosynthetic activity, they may lead to worse results in salt sensitive plants [58]. While the effect of Na+ ions may be negative in some plants, Cl<sup>−</sup> ion may be more negative in plants such as soybean and citrus [59]. Cl− ions can also deteriorate photosynthetic activity and may cause ion toxicity in plants like Na+ ions. In response to ion toxicity ABA hormone, which is produced by plant itself, is important. The amount of synthesis increases during stress, it is used to prevent disruption in the growth and development mechanisms of cell [60–61].
