Carbon dots enhanced cold tolerance of lettuce (Lactuca sativa L.): scavenging reactive oxygen species, modulating hormones and up-regulating gene expression

Abstract

Herein, carbon dots (CDs) improving lettuce (Lactuca sativa L.) growth and cold tolerance under low-temperature stress (4 °C) were investigated. After treatment at 4 °C for 12 hours, the dry and fresh weights of lettuce shoots were increased by 25.9% and 45.2%, respectively, and the dry and fresh weights of lettuce roots increased by 20.9% and 34.5% under foliar spraying of CDs (5 mg L⁻¹) compared with the control group. CDs can significantly scavenge reactive oxygen species (ROS) and reduce the content of malondialdehyde (MDA) by 19.7% in plants. The contents of sucrose, jasmonic acid, salicylic acid and proline were increased by 1.21, 2.95, 2.42 and 1.65 times upon exposure to CDs under low temperatures, respectively. In addition, the connection between CDs and proteins through hydrogen bonds was proved, which increased protein α-helices. Therefore, CDs activated the cold resistance signaling pathway (calmodulin (CAM)–calmodulin regulated receptor kinase signaling chain (CRLK)–mitogen activated protein kinase (MAPK)) through interaction with CAM and induced an increase in the contents of CAM, CRLK, and MAPK by 12.8%, 11.9% and 21.9%, respectively. Finally, CDs promote the expression of cold tolerance genes (C-repeat-binding factors (CBF) 8, CBF 12, and cold-regulated gene (COR) 413) up-regulated by 29.7%, 48.2% and 93.8%, respectively. Therefore, CDs can improve the cold resistance of lettuce by scavenging ROS, promoting plant hormone signal transduction, and interacting with calmodulin, which activates the cold resistance signaling pathway. These results demonstrate that CDs can be used as a promising agricultural fertilizer to improve plant response to climate change challenges.