Abstract: | In flowering plants, pollen germinates on the stigma and pollen tubes grow through
the style to fertilize the ovules. Enzymatic production of reactive oxygen species
(ROS) has been suggested to be involved in
pollen tube tip growth. Here, we characterized the function and regulation of the
NADPH oxidases RbohH and RbohJ (Respiratory burst oxidase homolog H and J) in pollen
tubes in Arabidopsis thaliana. In the rbohH and
rbohJ single mutants, pollen tube tip growth was comparable to
that of the wild type; however, tip growth was severely impaired in the double
mutant. In vivo imaging showed that ROS
accumulation in the pollen tube was impaired in the double mutant. Both RbohH and
RbohJ, which contain Ca2+ binding EF-hand motifs, possessed
Ca2+-induced ROS-producing
activity and localized at the plasma membrane of the pollen tube tip. Point mutations
in the EF-hand motifs impaired Ca2+-induced ROS production and complementation of the double mutant
phenotype. We also showed that a protein phosphatase inhibitor enhanced the
Ca2+-induced ROS-producing
activity of RbohH and RbohJ, suggesting their synergistic activation by protein
phosphorylation and Ca2+. Our results suggest that ROS production by RbohH and RbohJ is essential for proper pollen
tube tip growth, and furthermore, that Ca2+-induced ROS positive feedback regulation is conserved in the polarized
cell growth to shape the long tubular cell. |