Comparative anatomical and morphological studies of the epidermal and cortical parenchyma hypocotyl cells of two tomato genotypes (Solanum lycopersicum L.) under sodium chloride stress in vitro

Improving plant resistance to unfavorable environmental factors is one of the important tasks of modern agricultural production. The cultivated tomato is highly sensitive to salinity. Understanding the physiological, biochemical, molecular and genetic adaptive mechanisms of tomato resistance to salinity as a complex trait is an essential part of most fundamental studies, the results of which are increasingly finding practical application during the last decade. However, the data on the effect of sodium chloride on cell organization of different tomato tissues and organs are scarce. Thus, the purpose of the study was to investigate cell organization of the epidermis and parenchyma cortical tissues of tomato hypocotyl ( Solanum lycopersicum L. line YaLF and cultivar Rekordsmen) under chloride salinity in vitro. Fragments of 10-12-day-old aseptically germinated tomato seedlings, whose roots have been removed, were transferred on root induction medium (1/2 МS, 2 % sucrose, 0.2 mg/l indole-3-butyric acid) supplemented with 0-250 mМ NaCl. After 8 days in culture, middle part of hypocotyls were excised from rooted seedlings and prepared for light microscopy. Histological examination revealed significant differences between genotypes in shape and average cross-sectional areas of the epidermal and cortical parenchyma cells of hypocotyl. The addition of Na+ and Cl- ions to culture medium significantly affected the size of the intercellular spaces in the cortical parenchyma as well as the average cross-sectional areas and shape epidermal and cortical parenchyma hypocotyl cells of both tomato genotypes. The average cross-sectional areas of epidermal and cortical parenchyma hypocotyl cells of tomato line YaLF under 50 mM NaCl were significantly less (1,2 and 1,6 times, respectively) compared with control conditions (medium without NaCl). Epidermal and cortical parenchyma hypocotyl cells of tomato cultivar Rekordsmen decreased in size at higher concentrations of NaCl in the culture medium (100 and 150 mM NaCl, respectively). Dramatic increase in the cells areas of both tissue types of tomato line YaLF were observed under 250 mM NaCl salinity. In addition, under high salinity treatments there was a considerable change in the shape of epidermal (cells obtained angular contours) and cortical parenchyma hypocotyl cells (cell flattening) of line YaLF. Unlike line YaLF, the cross-sectional areas of epidermal and cortical parenchyma hypocotyl cells of tomato cultivar Rekordsmen was no statistically significant differences between 0 and 250 mM NaCl treatment. The dramatic difference between the two tomato genotypes was observed by a change in the cross-sectional areas of intercellular spaces in cortical parenchyma hypocotyl cells under salt treatments. Epidermal and cortical parenchyma cells of tomato hypocotyls cultivar Rekordsmen were less sensitive to the presence of NaCl in the culture medium, compared with the line YaLF. The revealed changes in shape and size of epidermal and cortical parenchyma hypocotyl cells can be used as cytological markers for comparative evaluation of tomato genotypes in sensitivity and/or resistance to salinity.