The morphology, distribution, and habitat of dwarf and normal forms of Fucus distichus in Nehalem Bay were examined. The dwarf form lacked the holdfast and sexual structures of the normal form and was more highly branched. Examples of the dwarf form were found growing as outgrowths of fragmented normal forms indicating that both forms are the same species. The normal form occurred attached to rocks near the mouth of the bay in waters of oceanic salinity. The dwarf form occurred as a free-living form in the salt marshes and in waters of lower salinity. These observations suggested that the occurrence of the dwarf form is related to salinity. Nutrient uptake studies with nitrate and carbon demonstrated that both forms have similar responses to changes in salinity. The dwarf form however, was better adaptated to the lower salinities than the normal form. Both forms showed a drop in carbon uptake and a slight rise in nitrate uptake as salinity was decreased, but the dwarf form maintained near maximal carbon uptake rates to a much lower salinity. It was shown that carbon uptake is sensitive to sodium and potassium ions, and nitrate uptake is sensitive to potassium ions. Reducing the sodium ion concentration by changing the medium composition decreased the carbon uptake rate. This rate was reduced further by the addition of potassium ion. The addition of sodium and potassium specific ionophores to the medium also depressed the uptake rate of carbon. Nitrate uptake was relatively unaffected by decreased sodium concentrations, but was drastically reduced by elevated potassium levels. The potassium specific ionophore valinomycin also produced a significant drop in the nitrate uptake rate. These data suggested that chemical potentials for sodium and potassium drive the uptake of carbon and that potassium is involved in the uptake of nitrate in F. distichus.

Pythium undulatum var. litorale Hohnk was found to infect Fucus distichus in the Squamish River estuary of southern British Columbia. This thesis adresses the questions of: 1.) whether this symbiosis can be found outside the Squamish River estuary, 2.) relationship of the infection within the estuary to the distribution of P. undulatum var. litorale in estuarine sediments, 3.) taxonomically defining those species associated with Fucus and/or in estuarine sediments, and 4.) the host parasite relationship as determined by means of histochemical and light microscope observations. Results indicated that outside the Squamish River estuary, associations between pythiaceous fungi and Fucus are uncommon in British Columbia coastal areas. Sampling of live and decaying Fucus plants from 10 field stations in British Columbia and Washington yielded only 4 species, the most common isolate being Phytophthora vesicula. Within the Squamish estuary, an association was found to exist between the distribution of P. undulatum var. 1itorale in the sediments and the distribution of infected Fucus plants. Sediment sampling from the Fraser River estuary, where Fucus does not occur, yielded P. undulatum var. litorale, suggesting that the fungus is probably indigenous to estuarine sediments. Numerous other species of Pythium were recovered from estuarine sediments, including P. butler i, P. carolinianum, P. catenulatum, P. gracile, P. torulosum , and P. volutum . Two taxa are described in detail. Pythium undulatum var. litorale was originally described by Hohnk (1953), but the varietal status was rejected by Waterhouse (1967). Arguments are presented for retention of the variety. Pythiogeten utriforme Minden is transferred to the genus Pythium and P. hohnkii is proposed as the nomen nova of this taxon. A discussion of the generic characteristics of the genus Pythiogeten is presented. In order to facilitate an understanding of the infection process by Pythium species, the anatomy and histochemistry of Fucus distichus were examined. Anatomically, F. distichus agrees with earlier reports of other species of Fucus. The internal structure of cells was found to agree with descriptions in earlier publications, although higher physode content was noted in F. distichus. Histochemical staining suggested that cell walls of Fucus are three layered; having an outer fucan-rich layer, a middle layer composed principally of alginic acid, and an innermost layer of cellulose. Several phenolic-indicating reagents were tested on both fresh and fixed/embedded Fucus tissue, resulting in some interesting new observations of phenolics in the matrix. The host-parasite interface of P. undulatum var. 1itorale and F. distichus was also examined by use of histochemistry and the light microscope. Macroscopically, the infection of F. distichus occurs behind the most recent dichotomy, and lesions are necrotic, firm (flaccid with age), and are pink-to-red in color. Microscopically, fungal hyphae are confined to the cortical and medullary regions. Hyphae appear to penetrate host cell walls by means of an enzymatic dissolution of the alginic acid and cellulosic portions of the cell wall. Use of the Periodic Acid/Schiff's reagent shows a distinct non-staining halo at the point where hyphae cross the cell wall. Pit connections between cortical cells were observed to break down with hyphae present in only one cell, suggesting that the fungus is capable of parasitizing several cells via digestion of pits. Gemmae were observed to form in both cortical and medullary cells. The response by Fucus to infection is an active one; a hypersensitivity reaction analagous to that of higher plants is observed. Cells in advance of fungal hyphae are observed to autolyse. Normally metabolically quiescent medullary filaments are observed to have an increase in general protein levels and to have increased physode content. Physodes become polarized within the medullary cells, and coalesce to form larger units, which are then delimited from the producing cell by a cross wall. The fate of these 'giant' physodes was not observed, but it is believed that these cells autolyse and release their phenolic contents to the matrix, as levels of phenolic-reactive material were observed to increase in this region. Coupled with the buildup,of phenolics in the matrix is a decrease in the fucan component of the matrix. Stress and tear lines appear between cells, and eventually this region serves as an abscission zone by which the infected portions are dropped out of the plant. Behind the abscission zone, medullary filaments undergo transverse divisions to form irregular, cuboidal cells which function as epidermis after abscission of the lesion occurs. / Science, Faculty of / Botany, Department of / Graduate