Salinity effects on protein content, lipid peroxidation, pigments, and proline in Paulownia imperialis (Siebold & Zuccarini) and Paulownia fortunei (Seemann & Hemsley) grown in vitro

We evaluated the effects of saline stress on soluble proteins, lipid peroxidation (TBAR), chlorophyll a, chlorophyll b, beta-carotene, violaxanthin, and proline in Paulownia imperialis and Paulownia fortunei plants grown in vitro. When the propagated plants reached a determined size, they were transferred aseptically to WPM culture medium containing different sodium chloride concentrations (0, 20, 40, 60, 80, and 160 mM) and were sampled at 15 and 30 days. Proline content was determined at 30 days after transfer only. Protein concentration significantly decreased with the highest salt levels in P. imperialis compared to controls in which no sodium chloride was added. In both P. imperialis and P. fortunei, lipid peroxidation significantly increased at 15 days but decreased at 30 days. Chlorophyll a, chlorophyll b, beta-carotene, and violaxanthin significantly decreased with exposure to higher sodium chloride concentrations at 15 and 30 days in both species. Proline content in P. imperialis significantly increased in plants grown in 20 and 40 mM of sodium chloride and decreased in higher sodium chloride concentrations. In P. fortunei, this measure significantly decreased proline content at all salt concentrations in plants exposed to all levels of sodium chloride compared to controls. Our results show that P. imperialis is more tolerant to salt stress at the salinity conditions tested.