A Review on the Impacts of Drought Stress on Seed Germination and Seedling Establishment in Medicinal Plants

Seed germination constitutes the most vulnerable phase in the ontogeny of medicinal plants, where drought stress simulated via polyethylene glycol (PEG-۶۰۰۰) at osmotic potentials (ψs) ranging from ۰ to -۲.۰ Mpa exerts profound inhibitory effects through reduced water uptake, oxidative burst, and metabolic perturbation. This systematic meta-analysis synthesizes quantitative data from ۷۲ peer-reviewed studies (۲۰۱۰-۲۰۲۵), encompassing ۲۸ medicinal species (e.g., Glycyrrhiza uralensis, Ocimum basilicum, Hyssopus officinalis, Dracocephalum moldavica, Eremosparton songoricum) across arid/semi-arid biomes. Key metrics include germination percentage (GP; ISTA criterion: radicle protrusion ≥۲ mm), germination index (GI = Σ(ni/ti); Ellis & Roberts, ۱۹۸۱), mean germination time (MGT = Σ(ni×ti)/Σni), seedling vigor index (SVI = GP × [radicle + hypocotyl length]), and biochemical markers (proline, MDA, SOD/CAT activity). Random-effects meta-analysis (n=۷,۲۰۰ seeds/experiment; I²=۷۴%) reveals biphasic responses: mild drought (-۰.۲ to -۰.۴ MPa) induces hormesis (+۱۲±۴% GP via antioxidant priming), moderate (-۰.۶ to -۱.۰ MPa) suppresses GP by ۵۲±۷% (Hedges' g = -۱.۶۸, ۹۵% CI: -۲.۰۱ to -۱.۳۵, P<۰.۰۰۰۱), and severe (<-۱.۲ MPa) arrests germination (GP<۱۵%). Tolerant genotypes (e.g., G. uralensis, EC۵۰ ψs = -۱.۱۵ MPa) exhibit ۳-fold proline accumulation (۳۵±۶ µmol/g FW), enhanced PIP۲ aquaporins, and LEA protein upregulation. Mitigation via osmopriming (PEG + ascorbate: +۴۸% GP recovery) and hydropriming (+۳۷%) is quantified. Recommendations integrate thermal time models (θT = ۴۵-۶۵ degree-days adjusted for ψs) with CRISPR-targeted DREB/ABF transcription factors for climate-resilient herbal agroecosystems in drought-prone Iran.

کلیدواژه ها:

Seed germination dynamics ، drought-induced osmotic stress ، polyethylene glycol