Effect of exogenously applied spermidine on growth and physiology of citrus rootstock Troyer citrange under saline conditions

The aim of this study was to assess the effects of spermidine (Spd) on ameliorating adverse effects of salinity in Troyer citrange seedlings. For this purpose, 6-month-old, uniform-sized seedlings of Troyer citrange were transplanted to plastic containers containing Hoagland nutrient solution. Addition of 75 mM NaCl into the nutrient solution reduced the plant growth, leaf chlorophyll content, chlorophyll fluorescence yield (Fv/Fm), net photosynthetic rate, respiration rate, and total Spd, N, and Ca2+ + Mg2+ contents of the leaves. It increased the leaf proline, total putrescine (Put), total spermine (Spm), Na+, and Cl- contents of the leaves. Addition of Spd (0.1 or 0.5 mM) to the saline nutrient solution and its weekly sprays (1 or 5 mM) on NaCl-stressed plants improved leaf number, chlorophyll content, Fv/Fm, net photosynthetic rate, and N content; increased total Spd and Spm contents; and reduced Na+ contents of the plants. Leaf Ca2+ + Mg2+ contents were slightly improved only when Spd (0.5 mM) was added to the saline nutrient solution. Leaf P and K+ contents were not significantly affected by the salinity or Spd treatments. Among the polyamines, Put content was least affected, while there was a sharp increase in Spm content due to the salinity and Spd treatments. These results suggest involvement of Spm in the salinity tolerance of citrus rootstock Troyer citrange.