Abstract
The spores of Lygodium japonicum, cultured in the dark, form a filamentous structure called protonema. Earlier studies have shown that gibberellin (GA) induces protonema elongation, along with antheridium formation, on the protonema. In this study, we have performed detailed morphological analyses to investigate the roles of multiple phytohormones in antheridium formation, protonema elongation, and prothallus formation in L. japonicum. GA4 methyl ester is a potent GA that stimulates both protonema elongation and antheridium formation. We found that these effects were inhibited by simultaneous application of abscisic acid (ABA). On the other hand, IAA (indole-3-acetic acid) promoted protonema elongation but reduced antheridium formation, while these effects were partially recovered by transferring to an IAA-free medium. An auxin biosynthesis inhibitor, PPBo (4-phenoxyphenylboronic acid), and a transport inhibitor, TIBA (2,3,5-triiodobenzoic acid), both inhibited protonema elongation and antheridium formation. L. japonicum prothalli are induced from germinating spores under continuous white light. Such development was negatively affected by PPBo, which induced smaller-sized prothalli, and TIBA, which induced aberrantly shaped prothalli. The evidence suggests that the crosstalk between these plant hormones might regulate protonema elongation and antheridium formation in L. japonicum. Furthermore, the possible involvement of auxin in the prothalli development of L. japonicum is suggested.
Highlights
Because Yamane et al [22] reported that abscisic acid (ABA) did not significantly inhibit the germination of L. japonicum spores in the range of 1 μM to 0.1 mM ABA under white light condition, 10 μM ABA was added to the culture medium to see any effects on the protonema growth
10 μM ABA drastically altered the tissue morphology (Figure S1), with the protonema length being reduced to 78.02 ± 10.79 μm (N = 76) (Figure 2A), approximately
These results indicated that GA was required for the formation of antheridium and antheridia were induced from certain cells after protonema elongation, and that auxin promotes cell division while inhibiting antheridium formation induced by GA
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. It has been reported that the expression level of gibberellin biosynthetic genes is increased in mature L. japonicum prothalli and that the expression level of GID1 is increased in immature prothalli [9] These studies hypothesized that archegonia formed in mature individuals secrete GAs, which accelerate the development of antheridia in the surrounding young individuals, leading to the production of sperm to be accepted by archegonia. Auxin-mediated signaling pathways for adventitious root development have been found to be conserved in Arabidopsis and the fern Ceratopteris richardi [20], suggesting that ferns should maintain similar genetic diversity of seed plants, with respects to reproductive organ formation. We have investigated how plant hormones GA, IAA, and ABA, which are known to be endogenous [12], are mutually interrelated in protonema elongation and antheridium formation in L. japonicum
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