# Redox Priming Ameliorates Salinity Tolerance of Seeds and Seedlings of the Coastal Halophyte Grass Urochondra setulosa

## TL;DR

This study shows that redox priming improves salt tolerance in Urochondra setulosa seeds and seedlings, making them more viable for use in coastal saline environments.

## Contribution

The novel contribution is demonstrating that redox priming agents like H2O2 and melatonin enhance germination and seedling vigor under salinity stress in a halophyte grass.

## Key findings

- Hydrogen peroxide priming significantly improved germination metrics under salinity stress.
- Melatonin priming enhanced seedling growth and pigment content under salt stress.
- Redox priming induced temporary dormancy in ungerminated seeds, which recovered fully in non-saline conditions.

## Abstract

Low salinity tolerance during germination and early seedling establishment limits large-scale cultivation of halophytes for forage, food, restoration, and conservation purposes. This study evaluates the potential of redox priming to enhance salt tolerance in the perennial C4 halophyte grass Urochondra setulosa, which could be used as a revegetation and phytoremediation crop for coastal saline lands. Fresh seeds were found to be non-dormant with ~90% mean final germination (MFG) in distilled water. Redox priming, including hydrogen peroxide (H2O2), melatonin (MT), sodium nitroprusside (SNP; a nitric oxide donor), and ascorbic acid (AsA), significantly accelerated the germination rate index (GRI) and reduced mean germination time (MGT) without altering MFG under non-saline conditions. Salinity severely suppressed germination, as unprimed seeds reached only ~1% MFG with ~99% germination reduction (GR) and near-zero germination stress tolerance index (GSTI) at 200 mM NaCl. All priming treatments significantly improved MFG, GRI, and GSTI and decreased GR, with H2O2 priming showing the highest amelioration. Ungerminated seeds from all treatments recovered ~90% germination capacity in water, indicating enforced dormancy owing to osmotic constraints. Salinity did not impair growth in unprimed seedlings. However, MT priming uniquely enhanced total length, leaf area, and seedling vigor index (SVI) at 200 mM NaCl, while MT and SNP priming resulted in the highest chlorophyll and carotenoid contents. Multivariate analyses confirmed MT’s consistent superiority across traits under stress. Thus, H2O2 priming optimizes germination, while MT priming improves seedling vigor and offers a practical, targeted strategy to improve early-stage salinity tolerance in U. setulosa for coastal revegetation and sustainable saline agriculture.