Proteomic analysis reveals that calcium channel blockers affect radicle protrusion during rice seed germination

Rice seed germination is regulated by numerous internal and external factors. Calcium ions (Ca2+), serving as an essential inorganic macronutrient and second messenger, are involved in the growth and development of plants. Calcium ions are predominantly stored in the cell wall and other organelles, such as vacuoles, mitochondria, and endoplasmic reticulum. Upon requirement, they are transferred from their storage location, where they are at high concentrations (mM), to the cytosol, where they are at lower concentrations (nM range). This study provides evidence that radicle protrusion is hindered in the presence of Ca2+ mobilization inhibitors during rice seed germination. A label-free quantification (LFQ) technique was used to investigate and characterize the importance of Ca2+ in rice seed germination through the suppression of their movement in the cell. After the extraction and digestion of total proteins, peptides were analyzed using nano-liquid chromatography (LC) coupled with tandem mass spectrometry (MS). A total of 667 proteins were significantly and differentially expressed under various treatments during rice seed germination. The functional analysis of these proteins indicated their involvement in various metabolic pathways, starch-sucrose metabolism, glycolysis-TCA, cadmium response, and other processes related to seed germination. Furthermore, the transcription levels of several calcium response genes were analyzed using quantitative reverse-transcription polymerase chain reaction (qRT-PCR) and compared to the abundance of corresponding proteins. These results could aid in understanding the role of Ca2+ in rice seed germination.