Elevations in cytosolic free calcium concentration constitute a fundamental signal transduction mechanism in plants; however, the particular characteristics of calcium ion (Ca²⁺) signal occurrence in plants is still under debate. Little is known about how stimulus-specific Ca²⁺ signal fluctuations are generated. Therefore, we investigated the identity of the Ca²⁺ signal generation pathways, influencing factors, and the effects of the signaling network under drought stress on Phyllostachys edulis (Carrière) J. Houz. Non-invasive micro testing and laser confocal microscopy technology were used as platforms to detect and record Ca²⁺ signaling in live root tip and leaf cells of P. edulis under drought stress. We found that Ca²⁺ signal intensity (absorption capacity) positively correlated with degree of drought stress in the P. edulis shoots, and that Ca²⁺ signals in different parts of the root tip of P. edulis were different when emitted in response to drought stress. This difference was reflected in the Ca²⁺ flux and in regional distribution of Ca²⁺. Extracellular Ca²⁺ transport requires the involvement of the plasma membrane Ca²⁺ channels, while abscisic acid (ABA) can activate the plasma membrane Ca²⁺ channels. Additionally, Ca²⁺ acted as the upstream signal of H₂O₂ in the signaling network of P. edulis under drought stress. Ca²⁺ was also involved in the signal transduction process of ABA, and ABA can promote the production of Ca²⁺ signals in P. edulis leaves. Our findings revealed the physiological role of Ca²⁺ in drought resistance of P. edulis. This study establishes a theoretical foundation for research on the response to Ca²⁺ signaling in P. edulis.

Phyllostachys edulis, an economically and ecologically significant bamboo species, has substantial research value in applications as a bamboo substitute for plastic and in forest carbon sequestration. However, frequent seasonal low-temperature events due to global climate change affect the growth, development, and productivity of P. edulis. Calcium signaling, serving as a versatile second messenger, is involved in various stress responses and nitrogen metabolism. In this study, we analyzed the calcium signaling dynamics and regulatory strategies in P. edulis under chilling stress. Differentially expressed genes (DEGs) from the CBF families, AMT families, NRT families, and Ca²⁺ sensor families, including CaM, CDPK, and CBL, were identified using transcriptomics. Additionally, we explored the law of Ca²⁺ flux and distribution in the roots of P. edulis under chilling stress and validated these findings by assessing the content or activity of Ca²⁺ sensor proteins and nitrogen transport proteins in the roots. The results indicated that the Ca²⁺ sensor families of CaM, CDPK, and CBL in P. edulis exhibited significant transcriptional changes under chilling stress. Notably, PH02Gene03957, PH02Gene42787, and PH02Gene19300 were significantly upregulated, while the expressions of PH02Gene08456, PH02Gene01209, and PH02Gene37879 were suppressed. In particular, the expression levels of the CBF family gene PH02Gene14168, a downstream target gene of the calcium channels, increased significantly. P. edulis exhibited an influx of Ca²⁺ at the root, accompanied by oscillating negative peaks under chilling stress. Spatially, the cytosolic calcium concentration ([Ca²⁺]_cyt) within the root cells increased. The CIPK family genes, interacting with Ca²⁺-CBL in downstream signaling pathways, showed significant differential expressions. In addition, the expressions of the NRT and AMT family genes changed correspondingly. Our study demonstrates that Ca²⁺ signaling is involved in the regulatory network of P. edulis under chilling stress. [Ca²⁺]_cyt fluctuations in the roots of P. edulis are induced by chilling stress, reflecting an influx of extracellular Ca²⁺. Upon binding to Ca²⁺, downstream target genes from the CBF family are activated. Within the Ca²⁺–CBL–CIPK signaling network, the CIPK family plays a crucial role in nitrogen metabolism pathways.