Effects of light quality, nitrogen source and Fe3+ concentration on female gametophyte development of Costaria costata

The female gametophytes of Costaria costata can be porpagated vegetatively by withholding inductive conditions, and also can be induced to produce gametes by providing the appropriate conditions. The change from vegetative to reproductive development has been attributed to various environmental factors, including light quality and nutrients. The experiment was conducted to test the combined effects of light quality (white light and blue light), nitrogen source (NaNO3 and Urea) and Fe3+ concentration (0, 0.1 and 0.5 mg L−1) in order to evaluate development performance of female gametophytes. When the female gametophytes and male gametophytes (mass ratio 2:1) mixed culture after 10 days, the number of female gametophytic cells remained constant and the apical part of cells elongated, while the male gametophytic cells remained in vegetative growth. The surface area of female and male gametophytes had increased in all treatments, ranging from 0.60 to 1.05 mm2 cm−2 and reaching a maximum under white light, CO(NH2)2 and Fe3+ 0.1 mg L−1. After 16 days, the female gametophytes developed oogonia and released eggs on the tip of the oogonia, while the male gametophytes developed spermatangia. The fraction of female gametophytes releasing eggs or forming sporophytes was determined as a measure of gametophyte phenology. A considerable proportion of female gametophytes (2.85%∼62.42%) had already formed oogonia and eggs at Fe3+ 0.1 mg L−1 and Fe3+ 0.5 mg L−1，particularly under blue light. The highest proportion with oogonia and eggs were observed at Fe3+ 0.5 mg L−1, blue light and CO(NH2)2 (22.12% with oogonia, 3.45% with eggs and 16.8% with sporophytes). On the 26th day, almost all female gametophytes cultivated at Fe3+ 0.1 mg L−1 and Fe3+ 0.5 mg L−1 in blue light developed a high portion of sporophytes (30.98%∼94.03%), while a significant lower portion of sporophyte at these Fe3+ concentrations in white light ranged between 10.97% and 42.59%. The density of sporophytes were maximal at Fe3+ 0.5 mg L−1, blue light and CO(NH2)2, but the length of sporophytes were maximal at Fe3+ 0.1 mg L−1, blue light and CO(NH2)2. In conclusion, the combination of blue light, Fe3+ 0.5 mg L−1 and CO(NH2)2 were favorable for female gametophyte development, which accelerated the process of gametophyte development and increased the final sporophyte growth.