Osmoprotective Mechanisms of Exogenous Proline in Salt-Stressed Physalis ixocarpa: Integrated Morphophysiological, Spectroscopic and Metabolomic Analysis

Soil salinization threatens agricultural sustainability in semi-arid regions where Physalis ixocarpa (Mexican husk tomato) represents an economically important crop. While exogenous proline enhances salt tolerance in various species, the underlying molecular mechanisms and metabolic trade-offs in P. ixocarpa remain unexplored. This study employed integrated morphophysiological, spectroscopic, and metabolomic approaches to elucidate proline's multifaceted protective mechanisms beyond simple osmotic adjustment.

Germination screening established moderate salt stress conditions, where proline pretreatment via seed imbibition substantially restored germination rates and seedling vigor. Subsequent in vitro culture experiments applied proline directly to salt-stressed seedlings, revealing an unexpected strategic trade-off: proline-treated plants prioritized photosynthetic protection over structural growth, achieving chlorophyll levels exceeding even non-stressed controls while reducing root biomass. This resource reallocation represents an energy-efficient stress tolerance strategy.

Infrared spectroscopy demonstrated proline incorporation into plant tissues and restoration of structural polysaccharide conformations disrupted by salinity. Metabolomic profiling uncovered fundamental biochemical reorganization: salt stress triggered shifts in primary carbohydrate identity and synthesis of nitrogenous osmolytes, while proline treatment reversed these changes and generated active proline-derived metabolites.

A key finding challenges conventional understanding of stress protection: phenolic antioxidants disappeared under salt stress and were not restored by proline treatment, yet plants showed enhanced tolerance. This suggests proline operates through preemptive metabolic stabilization rather than reactive antioxidant synthesis—a more cost-effective protective mechanism. These results provide practical protocols for enhancing salt tolerance through both seed priming and seedling treatment, with potential application in marginal growing conditions where water quality and soil salinity limit production.