Fern spore germination in response to environmental factors

Fern spore germination gives rise to the rhizoid and protonemal cell through asymmetric cell division, and then develops into a gametophyte. Spore germination is also a representative single-cell model for the investigation of nuclear polar movement, asymmetrical cell division, polarity establishment and rhizoid tip-growth. These processes are affected by various environmental factors, such as light, gravity, phytohormones, metal ions, and temperature. Here, we present a catalog of spore germination in response to different environmental factors. They are as follows: (1) Representative modes of light affecting spore germination from different fern species include red light-stimulated and far red light-inhibited spore germination, far red light-uninhibited spore germination, blue light-inhibited spore germination, and spore germination in the dark. The optimal light intensity and illumination time for spore germination are different among various fern species. Light response upon spore germination is initiated from the cell mitosis that regulated by phytochromes (PHYs) and cryptochromes (CRYs). AcPHY2, AcCRY3 and/or AcCRY4 are hypothesized to be involved in spore germination; (2) Gravity and calcium are crucial to early nuclear movement and polarity establishment of spores; (3) Gibberellin and antheridiogen can initiate and promote spore germination in many species, but abscisic acid, jasmonic acid, and ethylene pose only minor effects; (4) Spores can obtain the maximal germination rate in their favorable growth medium. Moreover, metal ions, pH, and spore density in the culture medium also affect spore germination; (5) Most fern spores germinate at 25°C, and an optimal CO2 concentration is necessary for spore germination of certain fern plants. These provide valuable information for understanding fern spore germination in response to environmental factors.