morpho-physiological responses and recovery of evening primrose (oenothera biennis l.) to water deficit and re-irrigation

Objective: evening primrose (oenothera biennis l.) is an important oilseed plant in temperate regions, facing challenges from drought and water scarcity. this study examined the effect of drought stress, sampling time, and accession type on vegetative, physiologic, and biochemical characteristics of evening primrose, and its recovery through re-irrigation.methods: experimental plants underwent four irrigation intervals (5 days as control, 10 days, 14 days, and 18 days) in gorgan, iran, using a factorial arrangement based on a randomized complete block design, with three replications. the pot experiment was conducted in a polyethylene-covered outdoor setting and continued until capsule formation. pre- and post-irrigation sampling allowed for the comparison of plant morphological, physiological, and biochemical characteristics in both iranian and german accessions.results: results showed no evening primrose recovery at the 18-day irrigation interval. extended watering cycles led to decreased leaf dry weight and membrane stability, and increased proline, total phenols, total flavonoids, and the activity of antioxidant enzymes catalase (cat), peroxidase (pod), superoxide dismutase (sod), ascorbate peroxidase (apx), and phenylalanine ammonia-lyase (pal). levels of proline, cat, pod, sod, apx, and pal varied significantly across different sampling times. accession differences were evident in antioxidant enzyme activities, reflecting distinct stress and recovery responses. recovered samples exhibited 1.3 times lower antioxidant activity compared to stressed samples. pal activity decreased after recovery, indicating improved photosynthetic efficiency after recovery.conclusion: drought stress decreased the vegetative growth and membrane stability, and increased the activity of various antioxidant enzymes, proline, phenols, proteins, and flavonoids. the increase in proline and antioxidant enzymes during drought stress suggests evening primrose's stress response and recovery capabilities. in gorgan's conditions, optimal evening primrose recovery intervals appear to be around 10 days, with potential recovery even at 14-day intervals. while understanding evening primrose recovery is critical, further investigations are necessary for making informed decisions in the field.