A simple experimental approach to simulate drought stress conditions in agar Petri dishes: characterization of the response in Medicago truncatula plantlets

Drought stress is the major factor in the reduction of crop yields causing significant economic losses. However, this stress is difficult to standardize under controlled conditions for research purposes. For molecular biology studies, which usually need highly standardized protocols for screening of large populations, PEG, mannitol or NaCl are employed to apply water deficit conditions. However, these osmolites do not properly simulate drought stress effects. In the present study, a simple experimental approach employing different agar concentration to simulate drought stress conditions in Petri dishes is tested with Medicago truncatula seedlings. The response of root morphology, respiration and drought stress markers is characterized under mild (≈ -1.0 MPa) and moderate drought (≈ -1,5MPa). Mild drought provoked an increase of root length that was not observed under moderate drought. Root area, volume and diameter decrease progressively with the increase of drought severity. Respiration rate was only significantly affected under moderate drought conditions, without changes in cytochrome and alternative pathways capacity. According to this, sucrose, malate and -ketoglutarate content decreased concomitantly with the increase of stress severity. Typical drought stress markers, as proline and amino acids, were also accumulated. Overall, these results validate this simple protocol to study drought stress response of seedlings under controlled conditions.