Calcium in Root Growth and Development

Calcium is an essential macronutrient that contributes to both the structural and biochemical components of the plant. It is an integral part of the cell wall and membranes, it acts as a critical counterion for both inorganic and organic anions, and it facilitates the activity of numerous enzymes. Additionally, Ca2+ is a central player in an almost bewildering array of cellular signaling networks that control aspects of root function from growth and development to defense. In recent years, researchers have made significant advances in dissecting this network of Ca2+-dependent activities down to the molecular machinery that makes it all work. This chapter discusses the current understanding of how roots take up and redistribute Ca2+ and then explores how Ca2+ acts as a key root signaling molecule using examples taken from root and root hair growth, defense against microbes and the establishment of root symbioses. The story that emerges is one of an increasing understanding of the molecular intricacies of the regulatory networks that support root function coupled with a recognition of the vast landscape of Ca2+-dependent systems that has yet to be explored.