ACTIN AND MYOSIN REGULATE PSEUDOPODIA OF PORPHYRA PULCHELLA (RHODOPHYTA) ARCHEOSPORES1

Archeospores of Porphyra pulchella Ackland, J. A. West et Zuccarello (Rhodophyta) display amoeboid and gliding motility. Time‐lapse videomicroscopy revealed that amoeboid cells extend and retract pseudopodia as they translocate through the media. We investigated the involvement of actin and myosin in generating the force for amoeboid motility using immunofluorescence, time‐lapse videomicroscopy, and cytoskeletal inhibitors. Actin filaments were seen as short and long rodlike bundles around the periphery of spores. The actin inhibitors cytochalasin D (CD) and latrunculin B (Lat B), and the myosin inhibitor butanedione monoxime (BDM) disrupted the actin filament network and reversibly inhibited pseudopodial activity, resulting in the rounding and immobilization of spores. It was uncertain whether forward translocation of archeospores resumed following drug removal. These results demonstrate that actin and myosin have a role in generating force for pseudopodial activity. This is the first report of cytoskeletal involvement in red algal cell movement. The involvement of actin and myosin in forward translocation of amoeboid archeospores can only be speculated upon.     

VARIATIONS IN THE CELL WALLS AND PHOTOSYNTHETIC PROPERTIES OF PORPHYRA YEZOENSIS (BANGIALES,RHODOPHYTA) DURING ARCHEOSPORE FORMATION1

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.     

Genetic similarity analysis within Pyropia yezoensis blades developed from both conchospores and blade archeospores using AFLP1

Pyropia yezoensis (Ueda) M. S. Hwang et H. G. Choi (previously called Porphyra yezoensis) is an economically important alga. The blades generated from conchospores are genetic chimeras, which are not suitable for genetic similarity analysis. In this study, two types of blades from a single filament of P. yezoensis sporophyte filament were obtained. One type, ConB, consisted of 40 blades that had germinated from conchospores. The other type, ArcB, consisted of 88 blades that had germinated from archeospores released from ConB. Both of them were analyzed by amplified fragment length polymorphism. The low genetic similarity levels for both conchospore‐germinated and archeospore‐germinated blades demonstrated that the conchcelis we used was cross‐fertilized. Furthermore, a higher polymorphic loci ratio (98.6%) was detected in ArcB than in ConB (80.7%), and the average genetic similarity of ArcB (average 0.61) was lower than that of ConB (average 0.71). These differences indicated that genetic analysis using ArcB gives more accurate results.     

‘Seed’ production of Porphyra spp. by tissue culture

Differentiation of archeospores was observed from excised tissue of young thalli of various monoecious Porphyra species ( P. tenera, P. yezoensis, P. suborbiculata, P. okamurae) after 4–8 days in culture at temperatures of 20 and 25 °C. Excised tissue from adult thalli did not differentiate into archeospores, but rather regenerated directly into blades and rhizoids of foliose thalli. Tissues from young thalli of two dioecious Porphyra species ( P. dentata and P. pseudolinearis) also regenerated into blades and rhizoids after manipulation of the culture conditions. In addition, 1–2 celled tissue pieces of both monoecious and dioecious species were also seen to develop directly into blades. Polarity of regeneration of blades and rhizoids was observed in these species. These results suggest that ‘seed’ can be obtained through tissue culture instead of using conventional conchocelis culture for commercial nori aquaculture in Japan. This revised version was published online in June 2006 with corrections to the Cover Date.     

Terminology used to describe reproduction and life history stages in the genus Porphyra (Bangiales, Rhodophyta)

An examination of the specific terms used to describe reproduction and life history in the red algal genusPorphyra is undertaken to clarify the subject. It is recommended that the terms carpospore and carposporangium are no longer used for this genus. The term phyllospore is proposed for spores produced in spore packets by the blade phase, unless the ploidy or subsequent development of the spores is known, in which case, the terms zygotospore, agamospore or neutral spore can be applied. It is recommended that the terms spermatia and spermatangia are used for male reproductive structures. Archeospores, endospores, protothalli, conchospores and neutral conchospores are also defined. This revised version was published online in August 2006 with corrections to the Cover Date.