Oxygen radicals and cytoplasm zoning in growing lily pollen tubes

Abstract

Recently redox-regulation of tip growth has been extensively studied, but differential sensitivity of growing cells to particular ROS and their subcellular localization is still unclear.Here we used specific dyes to provide mapping of H 2 O 2 and O • 2 ¯ in short and long pollen tubes. We found apical accumulation of H 2 O 2 and H 2 O 2 -producing organelles in the shank that were not colocalized with O • 2 ¯-producing mitochondria. Differential modulation of ROS content of the germination medium affected both growth speed and pollen tube morphology. Oxygen radicals affected ionic zoning: membrane potential and pH gradients. OH• caused depolarization all along the tube while O • 2 ¯ provoked hyperpolarization and cytoplasm alkalinization. O • 2 ¯ accelerated growth and reduced tube diameter, indicating that this ROS can be considered as pollen tube growth stimulator along with H 2 O 2 . Serious structural disturbances were observed upon exposure to OH• and H 2 O 2 and O • 2 ¯ quencher MnTMPP: pollen tube growth slowed down and ballooned tips formed in both cases, but in the presence of OH• membrane transport and organelle distribution was affected as well. OH•, thus, can be considered as a negative influence on pollen tubes which, presumably, have mechanisms for leveling it. The assumption was confirmed by EPR spectroscopy: pollen tubes actively reduce OH• content in the incubation medium.Recent studies of pollen tube growth have been attributed to internal and external signals affecting cytoplasm structural and functional as well as non-uniformly distributed ion currents. A number of data indicate the great importance of redox-regulation: ROS are produced on stigmas of various plants species during the pollination period

OsMTD2‐mediated reactive oxygen species (ROS) balance is essential for intact pollen‐tube elongation in rice

“…In addition, pollen‐tube rupture and sperm release were mediated by high levels of ROS at the entrance to the female gametophyte (Duan et al ., 2014). Different ROS can be considered to exhibit accelerating or decelerating influences on pollen‐tube growth, which possibly act in vivo as positive or negative signals controlling pollen physiology (Podolyan et al ., 2020). We observed that ROS became active in the endomembrane of rice pollen grain once it hydrates and is apically distributed in growing pollen tubes.…”

Pollen Germination and Pollen Tube Growth in Gymnosperms

“…A pronounced accumulation of H 2 O 2 was found in the apical cytoplasm of Picea pungens pollen tubes, superoxide radical is localized in mitochondria, and peroxide is also concentrated in amyloplasts [ 83 ]. In general, similar distribution is typical for flowering plants, for example, for lily [ 96 ].…”

Pattern of ROS generation and interconversion on wet stigmas in basal and divergent angiosperms

“…In case of SI pollination, ROS production was higher; exposure to antioxidants (Tezuka et al 1997) and inhibition of NADPH oxidase by cAMP (Tsuruhara et al 1999) allowed SI tubes to grow further into the style. On the other hand, in vitro pollen tube growth in lily was stimulated by superoxide radical and suppressed by hydroxyl radical (Podolyan et al 2021).…”