# Effects of High Lithium Concentrations on the Growth, Biomass, Mineral Accumulation, Oxidative Stress, Antioxidant and Gene Expression Response, and DNA Methylation in Sunflower Plants

## TL;DR

Sunflower plants respond to high lithium levels with changes in growth, stress responses, and DNA methylation.

## Contribution

The study reveals dose- and organ-specific physiological, molecular, and epigenetic responses to lithium in sunflower plants.

## Key findings

- Lithium concentrations above 5 mM impair germination, growth, and biomass accumulation in sunflower plants.
- Lithium disrupts mineral nutrient homeostasis and induces oxidative stress, with distinct antioxidant responses in leaves and roots.
- Lithium exposure causes organ-specific DNA methylation changes, with hypomethylation in leaves and hypermethylation in roots.

## Abstract

This study demonstrates that sunflower plants display integrated, multilevel responses to excessive lithium (Li) exposure. Li concentrations above 5 mM markedly impair germination, growth, and biomass accumulation. Li is preferentially accumulated in the shoots, showing high translocation and bioaccumulation factors, and disrupts mineral nutrient homeostasis, particularly potassium (K) and sodium (Na) uptake, while inducing oxidative stress. Although photosynthetic pigment contents decline, photosynthetic efficiency is largely maintained, except at 10 mM Li. Li treatment enhances superoxide anion (O2.−) and hydrogen peroxide (H2O2) production exclusively in leaves. Consequently, activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) increase in leaves, whereas only APX and GR are stimulated in the roots. Nitric oxide (NO) accumulation is detected only in leaves, while hydrogen sulfide (H2S) and glutathione (GSH) contents decline. Leaf ascorbate (AsA) levels decrease concomitantly with dehydroascorbate (DHA) accumulation. Expression analyses of catalase, DHAR, DHAR-like, and glutathione S-transferase (GST) genes confirm their involvement in Li stress responses. Moreover, global DNA methylation analyses reveal hypomethylation in leaves and hypermethylation in the roots. Overall, Li exposure induces dose- and organ-specific physiological, molecular, and epigenetic adjustments in sunflower plants under environmentally relevant concentrations and controlled experimental conditions in this study.