Full Recovery of Thallus Size After Desiccation by Fern Gametophytes

Researchers: Marinna Grijalva; Samuel Fitzgerald; Paola Moreno; Reem Al Dabagh; Stephen Davis; Helen I. Holmlund

Affiliation(s): Pepperdine University

Summary: Ferns exist in two life stages, the sporophyte and the gametophyte, and they are free living and independent of each other. The sporophyte is the vegetative body which is generally considered the “fern,” as it is readily visible in contrast to the cryptic gametophyte. Sporophytes are diploid and have true vascular systems, allowing them to survive in harsh environmental conditions. The gametophytic life stage is haploid, free of vascular tissue, and one cell layer thick; they use small rhizoids to anchor themselves to the substrate below them. Chaparral fern gametophytes are typically no larger than 5 millimeters in diameter and tend to grow in moist caves or crevices; this habitat protects them and therefore makes them very hard to find. It is not uncommon to find several gametophytes in a single cave. The desiccation tolerance mechanism of temperate gametophytes is largely unknown. We also do not know if desiccation tolerance in sporophytes indicates desiccation tolerance in their gametophytes.

The ecology and physiology of gametophytes is less understood compared to that of fern sporophytes. Most of the data which has been collected was derived from laboratory experiments; thus, a rebirth of field research is necessary in order to uncover the ecological niche of fern gametophytes. This is no easy task, as it requires extensive access to research sites and many discerning eyes in order to develop fruitful insight. There are various gametophytic growth forms seen in nature, but the most commonly seen shape in terrestrial fern species is an annual cordiform (heart-shaped) morphology (Farrar, 2008) which dies shortly after producing a single sporophyte. Chaparral fern gametophytes display this cordiform morphology and are often found glistening with droplets of water on their verdant surface. Gametophytes become nearly impossible to spot after they have desiccated in the field.

The purpose of this study is to examine the mechanism of desiccation tolerance in gametophytes by measuring thallus size as they desiccate and rehydrate in the Santa Monica Mountains. A gametophyte gradually folds when desiccating which likely protects its chloroplasts from damage and may reduce water loss, and so the potential for successful desiccation and resurrection may rely heavily on a natural drying process which would be difficult to replicate in the lab. A successful resurrection can be characterized and determined by measuring thallus size (mm2) and the maximum quantum yield of photosystem II (Fv/Fm) and comparing this data to that of a fully hydrated gametophyte prior to desiccation.

Link to full Poster on Study