## 4 Discussion  
Soil salinity stresses plants either because high concentrations of salts in the soil make it difficult for roots to extract water or because high concentrations of salts within plants can be toxic [64]. In this study, salinity resulted in lower leaf dry matter weight compared with normal conditions in the control treatment, but not lower shoot and root DW or relative growth rate of apple plants in terms of height. A rise in the salinity of soil is connected with a decreased rate of leaf growth owing to the osmotic effect of salt in the rhizosphere and consequently, leaf cells lose water. However, the loss of cell volume and turgor is transient, since these properties recur due to osmotic adjustment within hours, a finding which is not valid for cell elongation rates [65; 66; 67]. Decreases in cell elongation and cell division lead to a slower leaf emergence and a smaller final size over time [64]. At the same time, in the present experiment, no statistically significant differences in photosynthetic parameters were found between salinity and non-salinity conditions in the control treatment. Stable photosynthesis rates per unit leaf area in plants treated with salt is a frequent occurrence, whereas the changes in cell anatomy, the emergence of smaller, thicker leaves, and the resulting higher chloroplast density per unit leaf area could provide a possible explanation [68]. [PERSON] et al. [69] showed that mild water deficits had no effect on leaf gas exchange parameters in olive trees and, hence, suggested that their photosynthetic apparatus is very resistant to the stress in question. [PERSON] et al. [70] also concluded that the leaf internal CO\({}_{2}\) concentrations in flooded _Taxodium distichum_ seedlings remained relatively unchanged by different salt concentrations in the floodwater, despite reductions in stomatal conductance and photosynthesis. Organic solutes that are compatible with metabolic activity, even at high concentrations, accumulate in the cytosol and organelles, in order to compensate for the osmotic pressure of the ions of Na and Cl, which are confined in the vacuole in plants exposed to saline conditions [71; 72]. The compounds that have been associated with abiotic stress conditions and accumulate most commonly in plant tissues are sucrose, proline, and glycine betaine [64; 73; 74]. In plants under water deficit, proline often acts as an osmoprotectant that protects enzymes and proteins from denaturation [75]. However, in our study, a slight decrease, although not statistically significant, in proline concentration was observed in plants exposed to salinity compared with those grown under normal conditions in the control treatment. In glycopytes, the concentrations of the accumulating compatible solutes are in the order of 10 mM, on a tissue water basis. However, their potential compartmentalization exclusively to the cytoplasm could cause a significant osmotic pressure and an osmolyte function [64]. In parallel, it is considered that the compatible solutes either contribute to the conservation of the tertiary structure of proteins or function as osmoprotectants at low concentrations [76]. Nevertheless, the concentration of carbohydrates in leaves did not display significant differences among the treatments in our experiment, which complies with the assumption that some plants can adapt to salinity if exposed to low concentrations of salt. [PERSON] et al. [77] found that unadapted to salt, _Atriplex numum malaria_ cell cultures showed a dose-dependent inhibition of DW increase in the presence of 50-350 mM NaCl, and cells adapted to 342 or 428 mM NaCl were capable of sustained growth in the presence of salt. In parallel, the dwindling leaf area, which is associated with exposure to salinity, entails that the photosynthesis capability per plant is reduced resulting in a rise in the formation of reactive oxygen species (ROS) and of the activity of the respective detoxifying enzymes [78; 79].