Soil salinization and alkalization pose significant challenges to global agriculture. Grain amaranth (Amaranthus cruentus) has emerged as a promising crop for land affected by salinity and alkalinity because it can tolerate stress. However, few studies have examined the molecular mechanisms underlying its response to saline and alkaline stress.

In a study published in Plant Nano Biology on Sept. 14, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences found that foliar application of cerium oxide nanoparticles (CeNP) and zinc oxide nanoparticles (ZnONP) can significantly alleviate saline and alkaline stress in grain amaranth.

Through physiological, metabolomic, and transcriptomic analyses, the researchers revealed how the nanoparticles enhance the plant's ability to adapt to saline and alkaline environments by modulating antioxidant defense systems, ion homeostasis, and metabolic pathways.

The researchers used Amaranthus cruentus 'Zhongke Xian No.1' grown hydroponically. Starting two days before exposure to stress, the four-week-old seedlings received five foliar sprays of 75 mg/L CeNPs or ZnONPs at three-day intervals. The plants were exposed to saline stress, alkaline stress, or unstressed control conditions.

The results showed that both stresses inhibited shoot growth, with alkaline stress causing more severe inhibition. Both stresses also caused oxidative damage. Nanoparticle application enhanced antioxidant enzyme activities and reduced oxidative damage. The treatments also modulated proline and soluble sugar accumulation, improved water status, and partially restored endogenous auxin levels under stress.

Transcriptome analysis revealed that alkaline stress caused a greater transcriptional disturbance than saline stress. The application of nanoparticles substantially reshaped these stress-responsive patterns. Key gene networks involved in ion transport, reactive oxygen species detoxification, cell wall remodeling, and osmotic adjustment were enriched.

Overall, these findings suggest that CeNPs and ZnONPs can increase grain amaranth's resilience to saline and alkaline stress by regulating ion homeostasis, antioxidant defense, and metabolism related to carbon, hormones, and transport processes. CeNP was particularly associated with photosynthesis, carbohydrate metabolism, zeatin biosynthesis, and glycerolipid metabolism. ZnONP influenced a broader range of pathways, including amino acid and secondary metabolism, flavonoid biosynthesis, and cutin/suberin/wax pathways.

"Our study provides new insights into nanoparticle–plant interactions and supports the potential of engineered nanomaterials as complementary tools for crop production in saline and alkaline environments," said WAN Jinpeng of XTBG.

Grain amaranth at the saline-alkaline experimental site in Yuli county. (Image by WAN Jinpeng)

Grain amaranth at saline-alkaline experimental site in Alaer city. (Image by WAN Jinpeng)