Effects of NaHCO₃ stress on growth, photosynthesis and chlorophyll fluorescence characteristics in Populus davidiana × P. bolleana overexpressed TaLEA

In order to find the transgenic poplar which can tolerate soda-saline soil, the lines overexpressed TaLEA gene and the control (NT) were treated with NaHCO₃, the main components of soda-saline soil. And to evaluate salt-tolerant properties, we measured some parameters of different lines, including height and ground diameter, net photosynthetic rate(P_n), intercellular CO₂ concentration(C_i), stomatal conductance(G_s), transpiration rate(T_r), maximal photochemical efficiency(F_v/F_m), photochemical quenching coefficient (qP), non-photochemical quenching coefficient (NPQ), and the actual photochemical electron yield (Φ_PSII). Moreover, the accumulation of superoxide anion and hydrogen peroxide in each line was compared by staining method. The results showed that obvious changes had taken place in height and ground diameter among different lines after NaHCO₃ stress. There was no significant difference before treatment, but after treating for 20 days, significant differences happened. Compared with control, all transgenic lines increased in height and ground diameter, especially the SL2 transgenic line, whose average height and ground diameter were increased by 17.4% and 15.7%, respectively. Furthermore, the salt damage index of wild type was 3.3 times of transgenic lines, and the survival rate of transgenic lines was 2.8 times of wild type. The photosynthetic parameters and fluorescence parameters of the transgenic lines after 20 days stress were also higher than wild type, P_n and T_r were increased by 237.38% and 649.02%, respectively compared with the wild type. Compared with control, G_s and C_i of transgenic lines were increased by 119.05% and 24.56% under 15 days stress, and G_s, C_i of SL2 transgenic line were increased by 150% and 25.81%. Besides, the average F_v/F_m of each transgenic line was 0.68, the wild type was 0.45. The qP and PSII of transgenic plants were only slightly higher than that of the wild type, but the NPQ of wild type was 6 times of wild type.The accumulation of superoxide anion and hydrogen peroxide in transgenic lines was less than that in wild type. All in all, transgenic lines, especially SL2, could maintain rapid growth, strong photosynthetic capacity and lower level of ROS under alkali stress environment, so SL2 was initially selected as an excellent transgenic line of poplar because of salinity tolerance.