Calcium and the generation of plant form.

The involvement of mechanical signals (tension and compression) in the determination of the form of living organisms has been speculated upon for many years. These mechanical signals (both environmental and those generated within the plant itself) have significant effects on plant development and thus morphology. Plants respond to externally applied mechanical signals (touch and wind) by an immediate elevation of cytosolic calcium concentration ([Ca2+]eyt) in stimulated cells. This response requires the movement of plant tissues to cause tension and compression. Some of the more longer-term responses to mechanical signals, e.g. TCH gene expression and reduction in hypocotyl growth, show a calcium-dependency. It seems likely, therefore, that the effects of mechanical signals on plant development are mediated by the second messenger, calcium. This raises the exciting possibility that this simple ion plays a central role in the determination of plant form itself.