Susan Dunford, University of Cincinnati

Damaged sieve elements are sealed off by blocking the sieve plate pores with proteins and/or by the formation of callose in the pores. Another mechanism for blocking wounded sieve tubes occurs in plants in the legume family (Fabaceae). These plants contain large crystalloid protein bodies that do not disperse during development. However, following damage or osmotic shock, the protein bodies rapidly disperse and block the sieve tube. The process is reversible and controlled by calcium. Dispersal of the protein bodies can be triggered from a distance of several centimeters in broad bean (Furch et al. 2007). Wounding (burning) initiates an electropotential wave (action potential), which causes calcium release into the sieve elements, triggering the blocking response. While other plant families have protein bodies that do not disperse during development, it is not known whether other plants have similar mechanisms for plugging wounded sieve tubes. Since callose synthesis is also calcium dependent, wounding in broad bean further causes callose deposition in sieve pores following protein-body dispersal (Furch et al. 2007).