Impacts of priming on seed germination and seedling emergence of Cleistogenes songorica under drought stress

Cleistogenes songorica is an important native grass in northern China mainly used for regeneration of degraded land and in the grass-livestock industry. However, it is sensitive to drought stress during germination and early growth stages. Seed priming is a good approach to enhance germination and seedling establishment under stress conditions. Laboratory, greenhouse and field experiments were conducted to investigate the role of hydropriming, osmopriming and spermidine priming in enhancing germination, emergence and drought tolerance of C. songorica. Drought stress led to decreased germination and emergence, poor seedling growth, higher levels of lipid peroxidation and reactive oxygen species (ROS) accumulation. However, all seed priming treatments assuaged the detrimental effects of drought stress. Such improvements were associated with lower lipid peroxidation and generation of ROS (H2O2 content), and greater antioxidant enzyme activity in primed seeds under drought. Furthermore, an increase in the nuclear DNA contents of seeds from 2C to 4C occurred during priming, indicating progression from the G(1) to G(2) phase of cell cycle, the positive effect of priming was closely related to the percentage of cells at the G(2) stage of the cell cycle and to the G(2)/G(1), ratio.