[Sporopollenin accumulation in Nicotiana tabacum L. microspore wall during its development]

Accumulation of sporopollenin components in microspore wall, its polymerization dynamics and possible participation of reactive oxygen species (ROS) in this process has been studied. For this purpose fluorescent and electron microscopy (TEM) was used. It has been determined that phenylpropanoid components of sporopollenin that form the exine accumulate in the microspore cell wall at the middle and late tetrad stages. At the late tetrad stage, they fully cover the microspore surface and accumulate abundantly in aperture areas. In accordance with this, numerous thick sporopollenin lamellae, electron-dense and acetolysis-resistant, emerge in aperture areas. Exine in the areas between apertures includes both acetolysis-resistant sporopollenin and washout components. These particular parts of the wall are intensively stained with fluorescent dye MitoSOX, which detects the presence of ROS. The staining disappeared after the treatment of microspore with superoxide dismutase, demonstrating the presence of superoxide in the exine. Superoxide easily converts to hydrogen peroxide, which can cause oxidative polymerization of sporopollenin components, leading to the formation of chemically stable biopolymer. The data obtained favor the hypothesis of ROS involvement in the formation of sporopollenin.