The essay discusses the crucial role of calcium (Ca²⁺) in plant growth and development, highlighting its involvement in various cellular processes. Early studies in the 1950s and 1960s focused on the cell wall and membrane permeability, showing that Ca²⁺ is essential for maintaining cell wall structure and regulating membrane integrity. The discovery of the interaction between Ca²⁺ and pectin residues in the cell wall, as well as the role of Ca²⁺ in controlling membrane permeability, laid the foundation for understanding its regulatory functions. The essay also explores the broader context of Ca²⁺ as a second messenger in plant cell growth and development, tracing the historical development of this concept from animal cell physiology to plant cells. Key milestones include the demonstration of Ca²⁺ amplitude modulation in muscle contraction and non-muscle systems, followed by the identification of calmodulin and calcium-dependent protein kinases (CDPKs) in plants. These findings established Ca²⁺ as a key regulator in plant processes, including cell division, polarized cell growth, secretion, and interactions with plant growth regulators. The essay further discusses the importance of Ca²⁺ in light responses, homeostasis, and mitochondrial function, emphasizing the need for tight control over Ca²⁺ levels within the cell. Overall, the essay provides a comprehensive overview of the evolution of the understanding of Ca²⁺'s regulatory role in plant biology, from early observations to modern research.The essay discusses the crucial role of calcium (Ca²⁺) in plant growth and development, highlighting its involvement in various cellular processes. Early studies in the 1950s and 1960s focused on the cell wall and membrane permeability, showing that Ca²⁺ is essential for maintaining cell wall structure and regulating membrane integrity. The discovery of the interaction between Ca²⁺ and pectin residues in the cell wall, as well as the role of Ca²⁺ in controlling membrane permeability, laid the foundation for understanding its regulatory functions. The essay also explores the broader context of Ca²⁺ as a second messenger in plant cell growth and development, tracing the historical development of this concept from animal cell physiology to plant cells. Key milestones include the demonstration of Ca²⁺ amplitude modulation in muscle contraction and non-muscle systems, followed by the identification of calmodulin and calcium-dependent protein kinases (CDPKs) in plants. These findings established Ca²⁺ as a key regulator in plant processes, including cell division, polarized cell growth, secretion, and interactions with plant growth regulators. The essay further discusses the importance of Ca²⁺ in light responses, homeostasis, and mitochondrial function, emphasizing the need for tight control over Ca²⁺ levels within the cell. Overall, the essay provides a comprehensive overview of the evolution of the understanding of Ca²⁺'s regulatory role in plant biology, from early observations to modern research.