## 1 Introduction  
Salt concentration in saline soils has a negative effect on the biochemistry, anatomy and productivity of plants [1; 2; 3; 4; 5]. The increasing concentration of salt in soils is causing a considerable loss of agricultural potential worldwide, covering around 15% of the total agricultural area due to its increasing extent [6]. Salt and drought stress influence the accumulation of osmolytes and antioxidant compounds, such as flavonoids, at the cellular level. The stress effect of different concentrations of NaCl reduces the amount of chlorophyll, unlike drought stress [7]. Researchers have shown that high concentrations of NaCl decrease the mitotic index and increase the number of chromosomal aberrations [8; 9]. In addition, the effect of different amounts of NaCl leads to altered metabolic functions in plant tissues and a reduction in flavonoids [10]. Some studies have shown that foliar application of KNO\({}_{3}\) fertilizer has positive effects in combating salt stress [11]. These positive effects on NaCl stress have also been demonstrated using agmatine treatments [12]. Phytohormones also play an important role in abiotic stress tolerance, including salt tolerance. Previous studies have shown that the application of salicylic acid improved the growth of maize plants under salt stress [13; 14]. Several studies indicate that the effect of salt stress plays a role in the accumulation of reactive oxygen species (ROS), which leads to abnormalities in cellular cycles and influences plant growth [15; 16; 17]. Current research indicates a correlation between the increased accumulation of ROS and programmed cell death (PCD) in response to the effect caused by saline solutions [18; 19]. A cytological phenomenon correlated with abiotic or biotic stress in plant cells has been observed in the form of irreversible vacuolization of the cells. The initial physiological signal of vacuolization is determined by the presence of a greater number of provacuoles in plant cells when osmotic processes malfunction [20; 21]. Salt stress influences the vacuole formation process in plants cells [22]. However, vacuolization also occurs in animal cells in response to stress caused by various chemicals or by viral or bacterial infections [23]. Concerning studies showing that vacuolization is a characteristic phenomenon in the identification of cellular stress, including salt stress, numerous authors have described vacuolization in response to various stress factors in rice [24], wheat [25], vegetables [26], cotton [27], rapeseed [28], soybean [29] and maize [30]. Researchers have also observed that diets containing oil from the world's three main oil crops--rapeseed [31], soybean [32] and sunflower [33]--induced hepatocyte vacuolization. The sunflower (_Helianthus annuus_ L) belongs to the _Asteraceae_ family, and it is known for its quality and ease of oil extraction compared to other oilseed species [34]. The sunflower crop is used not only for oil extraction but also for seed production in human food [35; 36; 37] and as an ornamental plant [38]. All these reasons have led to the very large-scale cultivation of this species. Current sunflower breeding programs focus on the development of new genotypes, using in vitro biotechnology to develop genotypes tolerant to salt stress [39]. The aim of this research was to elucidate cellular physiological activities that can be used as starting points for identifying sunflower genotypes tolerant to different stresses, especially NaCl, in sunflower breeding programs. Cytological examinations of sunflowers and the use of biotechnological methods in sunflower breeding programs enable rapid cytological diagnosis and the selection of genotypes tolerant to salt stress. Vacuolization has not been used at all as a breeding method, nor has it been established whether it occurs under salt stress in the sunflower.