Pollen Projects

Self-Incompatibility in Poppy
A collaboration with Dr. Noni Franklin-Tong
University of Birmingham, UK
(see: http://www.biosciences.bham.ac.uk/staff/contact.html)

Signal perception and the integration of signals into networks effecting cellular changes is essential for all cells. In a recent study we have generated data that provide the first quantitative evidence for a specific stimulus-mediated depolymerization of actin filaments in plant cells. The self-incompatibility (SI) response in Papaver rhoeas pollen triggers a Ca2+-dependent signaling cascade resulting in inhibition of pollen germination and tube growth. The Franklin-Tong lab has previously observed SI-induced alterations in the actin cytoskeleton. By measuring the amount of F-actin in pollen grains and tubes before and during the SI response, we demonstrate that SI induction results in a rapid and sustained 56–74% reduction in F-actin levels. Actin depolymerization was also achieved by treatments that raise [Ca2+]i artificially. This provides a link between these two SI-induced events, suggesting that they are on the same signaling pathway. We suggest Ca2+-mediated depolymerization of F-actin as a molecular mechanism whereby SI-induced tip growth inhibition may be achieved. To understand this phenomenon further, we determined the cellular concentrations and binding constants for relevant proteins that might mediate actin depolymerization. Native profilin from P. rhoeas pollen is shown to have calcium-dependent monomeric actin sequestering activity, and its potential role during SI is reconstituted in vitro. However, profilin alone can not account for the level of actin depolymerization observed. We shall next examine the role of F-actin capping proteins and side-binding proteins during SI.

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