Dynamics of ROS production, SOD, POD and CAT activity during stigma maturation and pollination in Nicotiana tabacum...

Reactive oxygen species (ROS) are a key regulator of physiological processes in pollen grains, and an essential component of stigma exudate. The mechanisms of this redox-based regulatory system and its features in different plant groups are still unclear. For two species from different families (tobacco and lily), the dynamics of total ROS, O^• ₂ ^- generation, and H₂O₂ concentration in stigma exudate were examined using EPR spectroscopy and quantitative colorimetric analysis. Dynamics of all major enzymes of redox homeostasis were analysed using native electrophoresis and zymography for four stages of stigma development, before and after pollination. There were completely different patterns of ROS production and interconversion in the two species. In tobacco, the initially high level of ROS generation decreased before pollination but remained high. There was no CAT activity in fresh stigma tissues, which apparently contribute to the high level of H₂O₂. Lilium had peak O^• ₂ ^- generation at the fertile stage and high activity of H₂O₂-reducing enzymes, including CAT, hence, H₂O₂ level remained relatively low. We suggest that Lilium pollen germination is largely controlled by the SOD radical, while in Nicotiana H₂O₂ is the main form of ROS in the stigma.