Effect of ABA on the contents of proline, polyamines, and cytokinins in the common ice plants under salt stress

The effects of ABA treatment on the contents of proline, polyamines (PA), and cytokinins (CK) in the facultative halophyte the common ice plant (Mesembryanthemum crystallinum L.) subjected to salt stress were studied. Plants grown in the phytotron chamber on Jonson nutrient medium for 6 weeks were subjected to 6-day-long salinity by a single NaCl adding to medium. During first three days of salinity, half plants of each treatment were placed for 30 min on nutrient medium containing 0, 100, or 300 mM NaCl plus ABA in the final concentration of 1 μM. Salinity reduced biomass accumulation and water and chlorophyll contents in plants. This was accompanied by the increase in the levels of MDA, proline, and sodium ions. ABA treatment of salt-stressed plants favored biomass accumulation and photosynthetic pigment protection, reduced the intensity of oxidative stress and the level of NaCl-induced proline accumulation. ABA treatment increased the contents of putrescine (Put) and spermidine (Spd) in the leaves and roots of control plants (not subjected to salt stress), reduced the losses of Put in the leaves and roots and Spd in the roots in the presence of 100 mM NaCl, and suppressed cadaverine (Cad) accumulation in the roots in the presence of 300 mM NaCl. In the presence of NaCl, ABA reduced the contents of zeatin and zeatin riboside and increased the level of zeatin-O-glucoside in the roots and isopentenyladenosine and isopentenyladenine in the leaves. Thus, ABA protective action under salinity can be realized through the weakening of oxidative stress (a decrease in MDA content) and the regulation of PA, proline, and CK metabolism, which has a great significance in plant adaptation to injurious factors.