Physiological and proteomic responses to salt stress in chloroplasts of diploid and tetraploid black locust (Robinia pseudoacacia L.)

Salinity is an important abiotic stressor that negatively affects plant growth. In this study, we investigated the physiological and molecular mechanisms underlying moderate and high salt tolerance in diploid (2x) and tetraploid (4x) Robinia pseudoacacia L. Our results showed greater H2O2 accumulation and higher levels of important antioxidative enzymes and non-enzymatic antioxidants in 4x plants compared with 2x plants under salt stress. In addition, 4x leaves maintained a relatively intact structure compared to 2x leaves under a corresponding condition. NaCl treatment didn't significantly affect the photosynthetic rate, stomatal conductance or leaf intercellular CO2 concentrations in 4x leaves. Moreover, proteins from control and salt treated 2x and 4x leaf chloroplast samples were extracted and separated by two-dimensional gel electrophoresis. A total of 61 spots in 2x (24) and 4x (27) leaves exhibited reproducible and significant changes under salt stress. In addition, 10 proteins overlapped between 2x and 4x plants under salt stress. These identified proteins were grouped into the following 7 functional categories: photosynthetic Calvin-Benson Cycle (26), photosynthetic electron transfer (7), regulation/defense (5), chaperone (3), energy and metabolism (12), redox homeostasis (1) and unknown function (8). This study provides important information of use in the improvement of salt tolerance in plants.