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The Gametophyte of Pleopeltis lepidopteris (Langsd. & Fisch.) de la Sota (Polypodiaceae), a Fern from Restinga, after Spore Cryopreservation: Morphological, Ultrastructural, and Physiological Analyses

Premise of research. Pleopeltis lepidopteris (Langsd. & Fisch.) de la Sota (Polypodiaceae) is an important fern endemic to the restinga vegetation of southern Brazil. This moist broadleaf coastal forest has suffered strong human pressure, resulting in deforestation and even extinction of plant and animal communities. Therefore, this study aimed to explore whether cryopreservation in liquid nitrogen (LN) is an effective method of ex situ conservation of P. lepidopteris spores, maintaining their viability and physiological integrity.

Methodology. Spores were collected in March 2014 from the dunes of Joaquina Beach, Florianópolis, Santa Catarina, Brazil. Freshly collected spores were immersed in LN (−196°C) for 4 h, followed by thawing, to test germination. The morphology of cryopreserved (CR) and control (CT) spores after 4 d of cultivation, as well as gametophytes grown from CR and CT spores at 150 d, was analyzed by LM, CLSM, TEM, and SEM. In gametophytes at 150 d, chlorophyll a fluorescence was used to measure photosynthetic parameters as well as pigment content.

Pivotal results. No difference in germination was found between CR and CT spores. SEM analyses show that CT spores presented smooth spherical granules in the spore wall, while CR spores presented a rougher and more irregular spore-wall surface, indicating scarification. Accelerated growth and early onset of reproductive structures were observed in gametophytes from CR spores. No differences were seen in the ultrastructure of spores or gametophytes, either CT or CR. Similarly, no differences were seen in photosynthetic pigment content or photosynthetic parameters obtained from the analysis of chlorophyll a fluorescence for either treatment.

Conclusions. Based on these results, it can be concluded that cryopreservation proved effective for the ex situ conservation of P. lepidopteris spores, maintaining their viability and physiological integrity.