Calcium carbonate biomineralization is an ancient evolutionary feature of life that plays a key role in environmental adaptation. In plants, calcium carbonate deposition is found in several taxa; however, current knowledge of its formation and ecological adaptive implication is limited. Here, we used the chalk gland plant Ceratostigma willmottianum to gain insight into calcium carbonate biomineralization. We found that secretion crystals are mainly composed of calcium carbonate (>90%), and the chalk gland consists of 16 cells with 4 secretory pores on the surface. Calcium carbonate accumulation was highly dependent on atmospheric carbon dioxide and independent of soil dissolved inorganic carbon. Calcium carbonate accumulation occurred mainly during the day, with diurnal variations in the carbon source, mainly atmospheric carbon dioxide during the day and metabolic carbon dioxide at night. Hydration of carbon dioxide to bicarbonate (HCO3−) occurred within the leaves, and the reaction rate was controlled by the activity of extracellular carbonic anhydrases. C. willmottianum showed a high tolerance to calcium stress, potentially related to enhanced calcium compartmentalization and calcium carbonate excretion in the chalk gland under high-calcium environments. The conversion of atmospheric carbon dioxide into calcium carbonate by C. willmottianum may represent an ecological adaptation of plants to high-calcium environments. These results provide cases and theoretical references for studying calcium carbonate biomineralization mechanisms and plant calcium adaptation.

Low-temperature stress is a key environmental factor limiting the introduction and cultivation of plants native to tropical and subtropical regions; however, the molecular mechanisms governing their cold tolerance are not fully understood. In this study, we identified a core circadian rhythm gene—PiLUX—in the ornamental and medicinal plant Plumbago indica L. (P. indica) and systematically analyzed its role in the plant’s response to low temperatures. Transcriptomic analysis and physiological measurements indicated that PiLUX is significantly upregulated following cold induction; furthermore, its transcriptional levels show positive correlations with cold-tolerance-related physiological indicators such as reactive oxygen species (ROS) scavenging capacity, osmoregulatory substance accumulation, and membrane lipid peroxidation. In transgenic Arabidopsis thaliana (A. thaliana), heterologous overexpression of PiLUX enhances cold tolerance but also delays flowering, suggesting that reproductive development is sacrificed to conserve nutrients for cold tolerance. VIGS experiments confirmed that PiLUX knockdown exacerbates oxidative damage in P. indica under cold stress and reduces its recovery ability. The experimental results and transcriptomic data suggest that PiLUX may participate in the low-temperature response downstream of, or in parallel with, the CBF pathway; however, direct regulatory evidence is still required. This study provides insights into the adaptation strategies of thermophilic plants under low-temperature stress and offers a theoretical basis and genetic resources for cold-tolerance breeding in P. indica.