Effect of Drought Stress and Short-term Recovery on Proline and Polyamine Metabolism in Lotus japonicus

Environmental issues, particularly drought and soil salinity, severely limit plant productivity. This study aimed to examine the general reaction of legumes, specifically Lotus japonicus, against drought stress and their recovery following rehydration. After a 5-week culturing period, drought stress was simulated by withholding irrigation for 7 days. Stress response and recovery were evaluated through bioassays, and measurements of chlorophyll, proline and polyamine (stress reactants), and hydrogen peroxide and malondialdehyde (oxidative stress indices). Drought stress inhibited overall growth and decreased relative water content, but a recovery to control levels was observed after 8 h of re-watering. Hydrogen peroxide and malondialdehyde levels increased under drought stress, but showed no significant difference from control levels upon recovery. The accumulation of proline and polyamines was also observed, suggesting that they are effective responses to drought stress in plants. Furthermore, gene expression of key enzymes involved in proline and polyamine metabolism was regulated by stress conditions. By a short 8-h recovery period, the expression levels of metabolism-related genes of proline and polyamine returned to the pre-stress level, but the accumulation of functional substances was not induced. This study provides insight into the physiological and biochemical changes that occur in plants under drought stress and highlights the importance of proline and polyamine metabolism in plant adaptation to drought stress.