Signaling on the Stigma: Potential New Roles for ROS and NO in Plant Cell Signaling

Reactive oxygen species (ROS) and reactive nitrogen species, particularly NO, are key components of diverse signaling networks in animals and plants. We have recently shown that epidermal cells of stigmas from a range of different angiosperms accumulate relatively large amounts of ROS, principally H₂O₂, whereas pollen produces NO. Importantly, ROS/H₂O₂ levels appeared reduced in stigma cells supporting developing pollen grains compared to cells without pollen grains attached. To explore a possible link between pollen NO production and reduced levels of stigmatic ROS/H₂O₂, we supplied stigmas with NO and observed an overall reduction in levels of stigmatic ROS/H₂O₂. These new and unexpected data suggest a potential new signaling role for ROS/H₂O₂ and NO in pollen-stigma recognition processes.Key Words: stigma, pollen, reactive oxygen species, hydrogen peroxide, nitric oxide, signaling, defense