The role of nitric oxide in the germination of plant seeds and pollen

Two complex physiological processes, with opposite positions in the plant's life-cycle, seed and pollen germination, are vital to the accomplishment of successful plant growth and reproduction. This review summarizes the current state of knowledge of the intersection of NO signalling with the signalling pathways of ABA, GA, and ethylene; plant hormones that control the release of plant seeds from dormancy and germination. The cross-talk of NO and ROS is involved in the light- and hormone-specific regulation of seeds’ developmental processes during the initiation of plant ontogenesis. Similarly to seed germination, the mechanisms of plant pollen hydration, germination, tube growth, as well as pollen–stigma recognition are tightly linked to the proper adjustment of NO and ROS levels. The interaction of NO with ROS and secondary messengers such as Ca2+, cAMP and cGMP discovered in pollen represent a common mechanism of NO signalling. The involvement of NO in both breakpoints of plant physiology, as well as in the germination of spores within fungi and oomycetes, points toward NO as a component of an evolutionary conserved signalling pathway.

► NO and reactive oxygen species control the release of seed dormancy and seed germination.
► NOs signalling interplay with plant hormones abscisic and gibberelic acid.
► NO regulates catabolic enzymes of abscisic acid and biosynthesis of gibberelic acid.
► NO cross-talk with reactive oxygen species is a key step in pollen germination and tube growth.
► NO interact with pollen tube tip-oriented gradients of secondary messengers and chemical signals of stigma.