Programmed cell death is essential during plant development and in response to environmental ques and pathogen attack. Our lab studies plant tracheary element cells which undergo programmed cell death as a normal part of development. As a tracheary element differentiates, it constructs a rigid secondary cell wall and synthesizes a compliment of hydrolytic enzymes. After secondary cell wall synthesis is complete, the cell commits suicide. As you will see, the death of the cell is not a gradual process, but instead involves a rapid implosion of the large central vacuole and the immediate cessation of cytoplasmic streaming.
Water flows from the roots to leaves through the center of the cell corpses.
Details of tracheary element programmed cell death can be found in Groover et al. The movies that follow illustrate the rapid cell death of tracheary elements. The movies were made by isolating mesophyll cells from leaves of zinnia seedlings, then inducing them to differentiate as tracheary elements in culture with plant growth regulators. The cells were placed in a microchamber with a cover slip bottom and observed using an inverted microscope. In each movie, real time is recorded in the upper left-hand corner of the screen.