Integrated morphological, physiological and biochemical responses of parsley under drought stress

Abstract

Drought stress is a major abiotic factor affecting parsley (Petroselinum crispum) by disrupting its physiological and biochemical balance. This study aimed to investigate the integrated morphological, physiological, and biochemical responses of parsley cultivars differing in leaf morphology under contrasting irrigation regimes. Two irrigation levels—full irrigation (100% field capacity) and deficit irrigation (25% of full irrigation)—were applied to broad- and narrow-leaf cultivars under controlled growth conditions. Key parameters included relative leaf water content (RLWC), total phenolic and flavonoid contents, antioxidant activities (DPPH, ABTS), hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and the activities of antioxidant enzymes (SOD, APX, CAT) and polyphenol oxidase (PPO).

Drought stress reduced growth-related traits, with mean root length decreasing from 9.7 cm under full irrigation to 7.6 cm under water stress. Relative leaf water content (RLWC) was highest in the fully irrigated narrow-leaf cultivar (93.1%). Drought stress was associated with increased oxidative stress, with the highest numerical H₂O₂ content (6.85 ng mL⁻¹) and the highest MDA content (1.80 µmol mL⁻¹) recorded in the water-stressed narrow-leaf cultivar. SOD and APX activities decreased under water-deficit conditions, whereas PPO activity showed a predominantly cultivar-dependent pattern and CAT activity did not exhibit a consistent drought-induced increase. In contrast, flavonoid accumulation increased under water-deficit conditions. Treatment differences were evaluated using ANOVA followed by Tukey’s HSD test (p < 0.05).

These findings indicate that drought-induced reductions in plant water status were accompanied by increased oxidative stress and differential changes in enzymatic and non-enzymatic antioxidant responses, together with substantial growth inhibition in parsley. The broad- and narrow-leaf cultivars exhibited distinct response patterns, particularly in oxidative stress indicators and antioxidant-related traits, indicating cultivar-dependent responses to severe water deficit. Overall, the results highlight the importance of integrating morphological, physiological, and biochemical traits when evaluating parsley responses to drought stress. Nevertheless, further studies involving a wider range of genotypes and additional anatomical, physiological, yield-related, and field evaluations are needed to clarify and generalize the observed drought-response patterns.