Cadmium (Cd) causes serious damage to plants. Although calcium (Ca) signal has been found to respond to certain stress, the localization of Ca and molecular mechanisms underlying Ca signal in plants during Cd stress are largely unknown. In this study, Ca²⁺-sensing fluorescent reporter (GCaMP3) transgenic duckweed showed the Ca²⁺ signal response in Lemna turionifera 5511 (duckweed) during Cd stress. Subsequently, the subcellular localization of Ca²⁺ has been studied during Cd stress by transmission electron microscopy, showing the accumulation of Ca²⁺ in vacuoles. Also, Ca²⁺ flow during Cd stress has been measured. At the same time, the effects of exogenous glutamic acid (Glu) and γ-aminobutyric (GABA) on duckweed can better clarify the signal operation mechanism of plants to Cd stress. The molecular mechanism of Ca²⁺ signal responsed during Cd stress showed that Cd treatment promotes the positive response of Ca signaling channels in plant cells, and thus affects the intracellular Ca content. These novel signal studies provided an important Ca²⁺ signal molecular mechanism during Cd stress.

Dopamine (DA), a kind of neurotransmitter in animals, has been proven to cause a positive influence on plants during abiotic stress. In the present study, the function of DA on plants under cadmium (Cd) stress was revealed. The yellowing of duckweed leaves under Cd stress could be alleviated by an exogenous DA (10/20/50/100/200 μM) supplement, and 50 μM was the optimal concentration to resist Cd stress by reducing root breakage, restoring photosynthesis and chlorophyll content. In addition, 24 h DA treatment increased Cd content by 1.3 times in duckweed under Cd stress through promoting the influx of Cd²⁺. Furthermore, the gene expression changes study showed that photosynthesis-related genes were up-regulated by DA addition under Cd stress. Additionally, the mechanisms of DA-induced Cd detoxification and accumulation were also investigated; some critical genes, such as vacuolar iron transporter 1 (VIT1), multidrug resistance-associated protein (MRP) and Rubisco, were significantly up-regulated with DA addition under Cd stress. An increase in intracellular Ca²⁺ content and a decrease in Ca²⁺ efflux induced by DA under Cd stress were observed, as well as synchrony with changes in the expression of cyclic nucleotide-gated ion channel 2 (CNGC2), predicting that, in plants, CNGC2 may be an upstream target for DA action and trigger the change of intracellular Ca²⁺ signal. Our results demonstrate that DA supplementation can improve Cd resistance by enhancing duckweed photosynthesis, changing intracellular Ca²⁺ signaling, and enhancing Cd detoxification and accumulation. Interestingly, we found that exposure to Cd reduced endogenous DA content, which is the result of a blocked shikimate acid pathway and decreased expression of the tyrosine aminotransferase (TAT) gene. The function of DA in Cd stress offers a new insight into the application and study of DA to Cd phytoremediation in aquatic systems.

Sound vibration, an external mechanical force, has been proven to modulate plant growth and development like rain, wind, and vibration. However, the role of sound on plants, especially on signal response, has been usually neglected in research. Herein, we investigated the growth state, gene expression, and signal response in duckweed treated with soft music. The protein content in duckweed after music treatment for 7 days was about 1.6 times that in duckweed without music treatment. Additionally, the potential maximum photochemical efficiency of photosystem II (Fv/Fm) ratio in duckweed treated with music was 0.78, which was significantly higher in comparison with the control group (P < .01). Interestingly, music promoted the Glu and Ca signaling response. To further explore the global molecular mechanism, we performed transcriptome analysis and the library preparations were sequenced on an Illumina Hiseq platform. A total of 1296 differentially expressed genes (DEGs) were found for all these investigated genes in duckweed treated with music compared to the control group. Among these, up-regulation of the expression of metabolism-related genes related to glycolysis, cell wall biosynthesis, oxidative phosphorylation, and pentose phosphate pathways were found. Overall, these results provided a molecular basis to music-triggered signal response, transcriptomic, and growth changes in duckweed, which also highlighted the potential of music as an environmentally friendly stimulus to promote improved protein production in duckweed.

Cadmium (Cd) hampers plant growth and harms photosynthesis. Glutamate (Glu) responds to Cd stress and activates the Ca²⁺ signaling pathway in duckweed, emphasizing Glu’s significant role in Cd stress. In this study, we overexpressed phosphoserine aminotransferase (PSAT), a crucial enzyme in Glu metabolism, in duckweed. We investigated the response of PSAT-transgenic duckweed to Cd stress, including growth, Glu metabolism, photosynthesis, antioxidant enzyme activity, Cd²⁺ flux, and gene expression. Remarkably, under Cd stress, PSAT-transgenic duckweed prevented root abscission, upregulated the expression of photosynthesis ability, and increased Chl a, Chl b, and Chl a + b levels by 13.9%, 7%, and 12.6%, respectively. Antioxidant enzyme activity (CAT and SOD) also improved under Cd stress, reducing cell membrane damage in PSAT-transgenic duckweeds. Transcriptomic analysis revealed an upregulation of Glu metabolism-related enzymes in PSAT-transgenic duckweed under Cd stress. Moreover, metabolomic analysis showed a 68.4% increase in Glu content in PSAT duckweed exposed to Cd. This study sheds novel insights into the role of PSAT in enhancing plant resistance to Cd stress, establishing a theoretical basis for the impact of Glu metabolism on heavy metal tolerance in plants.