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A field, culture, and cytological study of Porphyra gardneri, Porphyra nereocystis and Porphyra thuretii (Rhodophyta, Bangiophycidae) Hawkes, Michael William


A field, culture and cytological investigation has been made of the life histories of Porphyra gardneri (Smith et Bollenberg) Hawkes, P. nereocystis Anderson and P. thuretii Setchell et Dawson, three superficially similar epiphytic red algae (Bhodophyceae, Bangiales). Porphyra gardneri was found from February through November, but is basically a spring-early summer species, Porphyra nereocystis is an autumn-winter species and P. thuretii is a winter-early spring species. The reported number of host species and geographical distribution is increased for all three species. A light microscope study of spermatogenesis and carposporogenesis was undertaken to characterize the spermatangium and carpogonium and to follow their division sequence. The spermatangium in Porphyra gardneri and probably P. thuretii is formed by the production of a new wall layer around a transformed vegetative cell. In contrast, no new wall layer is formed by P. nereocystis spermatangia, making them difficult to distinguish from vegetative cells. The carpogonium of P. gardneri and P. thuretii is easily recognized because it differentiates bipolar prototrichogynes. In P. nereocystis the carpogonium does not form prctctrichogynes and can only be distinguished from vegetative cells by its elongate, rectangular shape. On the basis of these observations and reports in the literature I suggest that the species of Porphyra can be separated into at least two groups based on their spermatangial and carpogonial morphology; the more advanced group has carpogonia with prototrichogynes and clearly defined spermatangia due to the deposition of a new wall layer, whereas the more primitive group lacks these features. The first division in both spermatogenesis and carposporogenesis is periclinal. This is discussed with respect to the division sequences reported by other workers. The transfer of Porphyrella Gardneri Smith et Hollenberg to Porphyra gardneri is explained on the basis of the observed mode of carpogonium formation and carposporangial division. Of the three species studied, only Porphyra gardneri produces monospores. Under all photoperiod and temperature regimes tested monospores germinated into the foliose phase. At an ultrastructural level monosporogenesis in Porphyra gardneri is characterized by the production of abundant small and large fibrous vesicles. The economic implications of monospore production are discussed. Field observations of Porphyra gardneri suggest that photoperiod is an important factor involved in inducinq the formation of spermatangia and carpogonia. A conchocelis phase is reported for the first time for Porphyra gardneri and Porphyra thuretii. Under all photoperiod and temperature reqimes tested carpospores qerminated into the conchocelis phase. In P. sardneri and P. thuretii short days favoured conchosporanqial branch formation; however, no such photoperiodic effect was observed for P. nereocystis., Although my results were inconclusive, reports in the literature indicate that temperature is a critical factor in conchospore release. Amoeboid movement of conchospores is reported for E°I£J3J£§ thuretii and discussed with respect to the occurrence of this phenomenon in the Rhodophyta generally. The epiphyte-'host' attachment zone of Porphyra gardneri and P. nereocystis was examined with the light microscope. The basal rhizoids of P. gardneri penetrate deep into the medulla of the Laminaria blade, whereas the rhizoids of P. nereocystis make only a superficial penetration of the Nereocystis stipe. The spermatia of Porphyra gardneri and P. nereocystis were examined ultrastructurally and found to have many similarities with Florideophycidae spermatia. The occurrence of fertilization in the life history of Porphyra gardneri is documented with the light and electron microscopes. A diploid chromosome number 2n=8 is reported for the carpospores and vegetative cells of the conchocelis phase P. gardneri. This is the first unequivocal report of sexual reproduction in the genus Porphyra. Suspected spermatia attached to the carpogonia and linked to them via fertilization canals have been observed in P. nereocystis and P. thuretii suggesting that sexual reproduction also occurs in their life histories. Reports of sexual reproduction in other members of the Bangiophycidae are evaluated in light of my observations.

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