Variations in the Cell Walls and Photosynthetic Properties of Porphyra Yezoensis (Bangiales, Rhodophyta) During Archeospore Formation1

Abstract

The formation of archeospores is characteristic of Porphyra yezoensis Ueda and is important for Porphyra aquaculture. Recently, it has been regarded as a valuable seed source for propagation of thalli in mariculture. Cell wall composition changes are associated with archeospore formation in P. yezoensis. Here, we report changes of cell walls of P. yezoensis during archeospore formation. The surfaces of vegetative cells that were originally smooth became rougher and more protuberant as archeosporangia were formed. Ultimately, the cell walls of archeosporangia ruptured, and archeospores were released from the torn cell walls that were left at distal margins of thalli. With changes in cell walls, both effective quantum yield and maximal quantum yield of the same regions in thalli gradually increased during the transformation of vegetative cells to archeospores, suggesting that the photosynthetic properties of the same regions in thalli gradually increased. Meanwhile, photosynthetic parameters for different sectors of thalli were determined, which included the proximal vegetative cells, archeosporangia, and newly released archeospores. The changes in photosynthetic properties of different sectors of thalli were in accordance with that of the same regions in thalli at different stages. In addition, the photosynthetic responses of archeosporangia to light showed higher saturating irradiance levels than those of vegetative cells. All these results suggest that archeosporangial cell walls were not degraded prior to release but were ruptured via bulging of the archeospore within the sporangium, and ultimately, archeospores were discharged. The accumulation of carbohydrates during archeospore formation in P. yezoensis might be required for the release of archeospores.

Comparative Gene Expression and Physiological Analyses Reveal Molecular Mechanisms in Wound-Induced Spore Formation in the Edible Seaweed Nori

“…At 4–5 days after wounding calcofluor white staining showed pre-spores enclosed in a thick cell wall forming packet structures resembling sporangia. After spore release, cell wall debris and the polysaccharide matrix remained in the intervening spaces ( Figure 1B ), consistent with observations of naturally releasing archeospores in Neopyropia ( Gao et al, 2011 ). Although the cell walls and matrix are not fully degraded, structural remodeling is required to facilitate spore release.…”

“…Both the cell wall and intervening space between cell “packets” became thicker and denser. This “packet” structure differs from typical archeosporangia in N. yezoensis , which contain only one differentiated spore ( Nelson et al, 1999 ; Gao et al, 2011 ), and more like the neutral sporangia in Porphyra umbilicalis ( Nelson et al, 1999 ; Royer et al, 2018 ; Figure 1A ). Without clear gene markers to distinguish spore types, we use the terms wound-induced spores (WIS) in this study.…”

RNA‐seq between asexual archeospores and meiosis‐related conchospores in Neopyropia yezoensis using Smart‐seq2

“…In the process of archeospore formation and release, the photosynthetic capacity increases gradually (Gao et al. 2011). These studies have indicated that archeospores have rapid growth characteristics.…”

“…Gao et al. (2011) have reported that photosynthesis gradually increases during the formation of the archeospores and its subsequent release from the thallus. Those studies have indicated that archeospores might have a growth advantage over conchospores, but molecular evidence remains to be established.…”

“…2008) and archeospores (Hawkes 1980, Gao et al. 2011) are cell wall‐free. In this study, we successfully obtained transcriptomic data for conchospores and archeospores of Neopyropia yezoensis using Smart‐seq2.…”