Response of Cleopatra mandarin seedlings to a polyamine-biosynthesis inhibitor under salt stress

Six-month-old, uniform-sized seedlings of Cleopatra mandarin growing in hydroponics in Hoagland nutrient solution under glasshouse conditions were subjected to salinity treatment (NaCl 75 mM). Addition of NaCl to the nutrient medium reduced plant growth (shoot height and leaf number), leaf chlorophyll content, chlorophyll fluorescence yields (Fv/Fm), net photosynthesis, stomatal conductance, transpiration rate, intracellular CO2 concentration, N, K+ and Ca2+ + Mg2+ contents of the leaves; and increased total putrescine (Put), proline and Na+ and Cl− contents of the leaves. Addition of d-arginine (1 mM) to the saline medium further reduced the values of all the parameters except Fv/Fm, photosynthesis and related parameters and Ca2+ + Mg2+ contents of the leaves, and increased total spermine (Spm) content of the leaves. However, total Put contents were decreased; spermidine (Spd) contents and Na+ and Cl− titres of the leaves were unaffected. Weekly spray of d-arginine (5 mM) was less harmful than its addition to the nutrient medium (1 mM). Addition of 0.5 mM Spd to the medium alleviated the adverse effects of d-arginine by improving plant growth, leaf chlorophyll content, total Put, Spd, Spm, N, P, K+ and Ca2+ + Mg2+ contents of the leaves. Weekly spray of Spd (5 mM) was less effective than its addition in the nutrient medium (0.5 mM).