Calcium: a central regulator of plant growth and development.

Today no one questions the assertion that Ca21 is a crucial regulator of growth and development in plants. The myriad processes in which this ion participates is large and growing and involves nearly all aspects of plant development (recent reviews in Harper et al., 2004; Hetherington and Brownlee, 2004; Hirschi, 2004; Reddy and Reddy, 2004; Bothwell and Ng, 2005). Despite this wealth of research, the concept of Ca21 as an intracellular regulator is relatively recent and within the professional life span of many people who are still active and working on this topic today. The aim of this essay is to identify those lines of thought and research that led to the idea that Ca21 is a second messenger in plant cell growth and development. This essay thus focuses primarily on work starting in the mid sixties and extending to the mid eighties. I do not provide an exhaustive review of the history of Ca21 research, nor do I attempt to treat modern aspects of Ca21 research. However, I do strive to identify the roots of modern Ca21 research and to chart the origin of the current revolution.