Organ-specific changes in the content of free and conjugated polyamines in Mesembryanthemum crystallinum plants under salinity

The content of free and conjugated polyamines (PA) was studied in the leaves of secondary shoots and in roots of the facultative halophyte Mesembryanthemum crystallinum L. under salinity. Plants were grown in water culture and at the age of 10 weeks were subjected to salinity stress by a single introduction of NaCl into nutrient medium to a final concentration of 400 mM. In 0, 6, 24, and 48 h, the content of free, HClO4-soluble, and HClO4-insoluble conjugates of PA were measured in leaves and roots. The levels of free and conjugated PA in the roots of control plants and plants subjected to salinity stress were higher than in the leaves. In response to salinity shock, the content of all forms of spermine (Spm), particularly its HClO4-soluble conjugates, increased in roots and leaves. In contrast, the content of Spm precursors, putrescine (Put) and spermidine (Spd), as well as their HClO4-soluble conjugates, decreased. Salinity treatment elevated the content of free cadaverine both in roots and leaves, whereas the content of its conjugated forms decreased, which might suggest transition of conjugated forms of cadaverine into the free form. The product of oxidative degradation of Spm and Spd, 1,3-diaminopropane (Dap), was absent in leaves, whereas the content of free and conjugated forms of this diamine in roots increased under salinity conditions. The obtained data indicate organ specificity for the content of free and conjugated forms of PA, as well as their active role in adaptation of Mesembryanthemum crystallinum to salinity shock.