Endangered Salvia daiguii Has Evolved Drought Tolerance Through Photosynthetic, Antioxidant, and Respiratory Adaptations: Implications for Ex Situ Propagule Reintroduction

Abstract

Salvia daiguii is an endangered plant species with medicinal potential, whose ex situ conservation and reintroduction are essential for population restoration. However, drought tolerance, critical to the survival and establishment of reintroduced populations, remains poorly understood for S. daiguii. Using PEG-simulated drought treatments (0–15%), we evaluated physiological drought tolerance mechanisms of S. daiguii with its drought-tolerant congener Salvia meiliensis as a reference. Drought injury indices increased with rising PEG concentrations in both species, yet S. daiguii showed stronger drought tolerance across 5–15% PEG, as evidenced by milder injury, less thiobarbituric acid-reactive substances (TBARS), and higher relative water content in aboveground tissues. Though both species exhibited adaptive drought responses, their response patterns and magnitudes differed. At 10% PEG, S. daiguii had higher peroxidase (POD) and ascorbate peroxidase (APX) activities. It accumulated more ascorbate (AsA), soluble sugar, and soluble protein at 10% and 15% PEG and maintained advantages in chlorophyll accumulation and respiratory enzyme activation across all PEG treatments. Higher glutathione reductase (GR) activity in S. daiguii at 10% and 15% PEG accelerated glutathione (GSH) regeneration, strengthening its antioxidant capacity. Collectively, the superior drought tolerance of S. daiguii involves integrated modulation of photosynthetic, antioxidant and respiratory systems, supporting its conservation and reintroduction.