# Polyamine Homeostasis and Morphophysiological Responses to Salinity in Dizygostemon riparius: An Endemic Species from Brazilian ‘Cerrado’ Biome

## TL;DR

This study explores how a Brazilian plant species responds to salt stress in a lab setting, revealing its sensitivity and potential for cultivation optimization.

## Contribution

The study provides the first data-driven characterization of salinity effects on Dizygostemon riparius using in vitro culture.

## Key findings

- Salinity significantly reduced biomass and growth parameters in D. riparius.
- Photosystem II efficiency and chlorophyll content declined under salt stress.
- Polyamine metabolism was altered, indicating limitations in defense mechanisms.

## Abstract

Dizygostemon riparius, also known as “melosa”, is a subshrub endemic to the Brazilian ‘Cerrado’ with great medicinal and agrochemical potential due to their essential oils, which have biopesticide activity. Due to its recent cataloging, there is a huge gap regarding its cultivation and responses under adverse conditions, such as salinity, including under in vitro conditions—a biotechnological approach widely used in the production of essential oils, which in some cases can be enhanced by salinity. Thus, this study aimed to address how D. riparius cultured in vitro responds to salinity stress by evaluating the growth, photosynthesis, and homeostasis of polyamines—a group of plant hormones involved in stress responses. Despite the thickening of the leaf epidermis—a common defense response to salinity—our results indicate that this species is sensitive to salinity, as shown by the impairment of growth and photosynthesis, and decreases in chlorophylls and polyamine contents. These findings pave the way for better understanding the in vitro cultivation of this tropical species, helping to optimize cultivation protocols in saline-prone regions, such as the Tropics, and ultimately contributing to the knowledge about the flora of the Brazilian ‘Cerrado’, a unique and emblematic biome.

Dizygostemon riparius is an endemic tropical Brazilian species whose physiological responses to salinity are poorly understood. This study evaluated the effects of NaCl (0, 50, and 100 mM) on in vitro-grown D. riparius by integrating growth, anatomical, photosynthetic, and biochemical analyses. Salinity significantly reduced biomass and growth parameters, indicating impaired development. Photosystem II efficiency declined, as evidenced by decreases in the performance index and chlorophyll content, while anatomical changes such as epidermal thickening and reduced vascular bundles reflected structural adjustments under stress. At the biochemical level, salinity altered polyamine metabolism, with reductions in total free polyamines, suggesting potential limitations in defense mechanisms. Hyperhydricity observed under high salinity indicated a non-adaptive response. Overall, D. riparius displayed limited tolerance to salt stress, with physiological and biochemical impairments outweighing structural plasticity. This study provides the first data-driven characterization of salinity effects in this species and highlights the value of in vitro culture as a tool to investigate stress responses.