Hot-water extraction of Anatheca dentata, a red seaweed belonging to the family Solieriaceae, yielded a mixture of polysaccharides. Fractionation of this mixture with Cetavlon gave a glucomannan as minor component and a highly sulphated major component, which gave D- and L-galactose, D-xylose and small amounts of 3-0 (underscore)-methylgalactose, pyruvic acid and uronic acid on hydrolysis. All subsequent investigations were carried out on the sulphated major component. The sulphate was not labile to alkali, but was removed with methanolic hydrogen chloride. Periodate oxidation of the polysaccharide before and after desulphation indicated that new a-glycol groups were formed during desulphation. All the xylose units in the polymer were cleaved by periodate and this, together with the fact that the major xylose product from methylation analysis of the desulphated polymer was the 2,3, 4-tri-0 (underscore)-methyl derivative, indicated that the xylose occurs as a non-reducing end-group. Methylation of the desulphated polysaccharide revealed the presence of 1,4- and 1,3- linked D- galactose and 1,4- linked L-galactose units in the polymer. D-Glucuronic acid occurred as non-reducing end-groups. Summary, p. 1.

Various aspects of the biology of the intertidal agarophyte, Gelidium pristoides, were investigated, with the aim of providing information that would assist in formulating a management policy for this economic seaweed resource. G.pristoides occurs as tufts comprising as many as 40 individual plants, representing all three conspicuous life history stages, that are linked by the intertwining of their basal creeping axes. Individual plants consist of a system of branched creeping axes, which is largely responsible for colonizing surrounding substrata, from which one or more erect flattened fronds arise. These erect fronds may reach a height of 15 cm, and are irregularly bipinnately branched. Internal vegetative anatomy is generally typical of the genus. Morphological variation in mature plants is limited to increased plant height and branch density during the summer season. A dorso-ventrally flattened creeping habit was seen during early recruitment on flat rock surfaces and limpet shells within grazer exclusion plots, which developed into typical erect plants. Although there is a close taxonomic affinity between G.pristoides and the low-growing Gelidium turf, which occurs on wave-cut platforms in the eastern Cape (both produce bispores), the turf appears to represent a genetically divergent ecotype of the typical G.pristoides habit. In the light of present observations, it is suggested that the recent inclusion of G.pristoides in the new Onikusa genus should be questioned. Reproduction in G.pristoides is typical of the genus, except for the production of bispores, instead of tetraspores, in the sporophyte generation. The smaller nuclei in the binucleate bispores, in comparison to carpospores, suggested they are the product of normal meiosis (meiospores). This was confi rmed by chromosome counts of germl i ngs deri ved from bispores (n = 13-17) and carpospores (2n = 28-33). Throughout the geographical range of the seaweed, the bisporophyte generation is dominant over the combined male and female gametophyte generati on by a ratio of about 3 : 1. This imbalance may be due to bispores. G.pristoides a greater germination success of carpospores over plants are fertile throughout the year, while at Port Alfred there is no apparent seasonality in spore release. Growth of carpospore and bispore germlings is similar under various temperature treatments in culture. Optimum temperatures for growth were from 15-23°C, which corresponds with the sea temperatures experienced within the geographical range of the species . At Port Alfred, growth (linear frond elongation) and standing crop levels were maximal during summer . Ory weight levels were significantly inversely related to both growth and ash levels. Agar contents (% of dry weight) were generally greater in summer (48% ) than in winter (30%), and were inversely correlated with thallus nitrogen levels. Agar contents of distal plant halves were higher (8-15%) than in proximal halves. Regrowth of G.pristoides to original biomass or standing crop levels after harvesting, is similar for plucking and shearing at different times of the year. Regrowth is more rapid after spring and summer harvests (2-3 months) than after winter harvests (4-5 months). During the summer season, harvesting at monthly intervals showed significantly greater total yields, and production rates (e.g . 3.13 g. dry wt. / m2 / day for plucking) than under 3-monthly intervals (1.42 g. dry wt. / m2 / day for plucking). In contrast, average yields per harvest were Significantly greater when recovery period was longer (e.g. 3 months). Quadrats that were completely denuded failed to recover after a year, while regrowth was also retarded with increased elevation on the shore. Agar contents did not differ Significantly between plucked (38%) and sheared (42%) plant material. G.pristoides is distributed from about 0 . 2-0.75 m above MLWS, with a reduction in stature and frequency corresponding to increased elevation on the shore. Frond elongation rates, germling survival and recruitment within grazer-exclusion plots, is retarded with increased elevation level. Plants transplanted above the normal vertical range of the seaweed became severely bleached and died, while plants transplanted below the normal range of the seaweed (sub littoral fringe) senesced due to overgrowth by the epiphytic encrusting coralline, Polyporolithon patena (Hook . et Harv . ) Mason . G.pristoides recrui t ment in the sublittoral fri nge was enhanced with the exclusion of grazers . However, successful recruits were displaced due to smothering by articulated corallines (e.g. Corallina sp. and Jania sp. ) . G.pristoides is largely restricted to cracks and crevices in the rock, and also occurs on a large proportion of the available shells of the limpet Patella oculus Born., and to a lesser extent, shells of the barnacle Tetraclita serrata. G.pristoides recruitment was significantly enhanced by the exclusion of grazers (using toxic antifouling paint barriers). G.pristoides recruitment within the exclusion plots was significantly greater on artificially attached limpet shells (almost 100% cover) than on rock surfaces (20-30% cover), which occurred largely within cracks and crevies in the rocky substratum. ly attached to limpet G.pristoides plants are significantly more strongand barnacle shells than to rock and epilithic encrusting corallines (Lithothamnion sp.). Removal of G.pristoides from limpet shells revealed pits of a uniform size in the surface of the shells, into which the rhizoidal attachment organs of the seaweed penetrate. It is concluded that the horizontal distribution of G.pristoides is largely controlled by grazers (and "escapes" from grazing) and resistance to dislodgement by wave action. Based on present results, and considering some of the socio-economic factors associated with the Gelidium industry in South Africa, suggestions are made concerning the management and long-term maintenance of G.pristoides resources in the eastern Cape.

Several aspects of L-threonine dehydratase from seven species of unicellular marine planktonic algae were investigated; (1) the disulfide group requirement for activity of the enzymes from two cryptomonads, (2) monovalent inorganic cation requirement for enzyme activity, (3) substrate specificity and substrate analog inhibitions, (4) allosteric activation and inhibition and diverse effects from other amino acids, (5) pH optima of the algal enzymes with particular emphasis on the elucidation of the unique pH-activity response of the enzyme from Hemiselmis virescens. The threonine dehydratases from Chroomonas salina and Hemiselmis virescens require disulfide groups for enzyme activity as exemplified by the specific inhibition exerted by all thiol reagents tested, which inhibition could be partially reversed or prevented by the appropriate treatments. Sulfhydryl group requirement: for enzyme activity was confirmed and it was demonstrated that these groups are essential for feedback inhibition from L-isoleucine. All algal enzymes appear to require monovalent alkali-metal cations for full expression of activity, more specifically K⁺₄ and NH⁺₄. Anacystis marina was exceptional in showing maximal stimulation from Li⁺. Organic cations were without effect whereas some inhibition from certain divalent cations (Zn²⁺ , Cu²⁺) and anions (N0⁻₃, I⁻ , C10⁻₃) were observed, whilst HP0²₄⁻ and SO²₄⁻ were stimulatory. Aside from L-threonine, the algal enzymes extended substrate activity to L-serine and L-aliothreonine. In addition to its known threonine dehydratase, Chroomonas salina appeared to produce a serine dehydratase which accounted for the relatively high substrate activity observed toward L-serine with this species. Inhibition from substrate analogs was limited to L-homoserine and L-serine, despite the substrate activity of the latter. The mechanism for the peculiar mode of inhibition evinced by L-homoserine remains unknown whereas that of L-serine appears to result from inactivation of the enzyme. With the exception of Cyclotella nana and to a lesser extent Hemiselmis virescens, all the algal enzymes were subject to feedback inhibition from L-isoleucine, which inhibition was pH dependent, subject to reversal by L-valine, and could be duplicated by the analog L-O-methyl threonine. Several other amino acids (L-leucine, L-norvaline, L-valine) were able to inhibit most enzymes when present at high concentration. It was proposed that the mode of inhibition by these latter amino acids may occur via interaction at the site specific for allosteric inhibition. L-Valine at low concentration effected pronounced activation of the enzymes and was thusly assigned the role of allosteric activator, acting at a site distinct from that of L-isoleucine or L-threonine. Hemiselmis virescens was distinctly unique in that, unlike the other algal enzymes, it displayed two pH-activity optima. The investigation of this phenomenon was pursued in two ways (i) examination of enzyme response to various potential effectors (nucleotides, L-methionine, L-aspartate,^ L-cystathionine) at a pH intermediate between the two optima, (ii) examination of enzyme response to known effectors (L-valine, L-isoleucine) at the two pH optima. It was concluded from these studies that Hemiselmis virescens may produce a culture-dependent mixture of two threonine dehydratases, one of which is generally similar to the other algal enzymes, the other of which is insensitive to the usual allosteric regulation yet is not a standard biodegradative isozyme. / Land and Food Systems, Faculty of / Graduate

Consumers are concerned about antibiotic and ractopamine usage; therefore, alternatives need to be found. Objectives of this study were to investigate the effects of using seaweed as an alternative feed supplement and comparing performance, carcass, pork quality, and immune traits in pigs fed seaweed, control, and ractopamine diets. Pigs were allocated to one of three treatments (CON, SWE, RAC) at weaning (n = 40/treatment). Pigs were weighed every two weeks. Carcass characteristics, pork quality, and immune data were collected post-mortem. No differences were found between treatments for feed intake, growth, or feed efficiency. Pigs on RAC treatment had greater hot carcass weight and dressing percentage (P < 0.05). Chops from RAC pigs were lighter (P = 0.05), less red (P < 0.05), and tougher (P = 0.08). There were no differences between treatments for FABP2 gene expression, cell proliferation percentages, or crypt depths. Therefore, no negative effects of feeding seaweed to pigs were found in this study.

Temporal variability in nutrient supply has not generally been considered to be a factor controlling macroalgal community structure. Frequent sampling in environments with multiple nitrogen (N) inputs reveals that N supply varies greatly on scales of hours, days and weeks. This thesis describes studies of the adaptations of macroalgae to variability in N supply and the effects of this variability on the species composition of a macroalgal community. A study was made of the efficacy of using N flux (water flow rate X N concentration) to predict the growth rate of Gracilaria tikvahiae (Rhodophyta). The relationship between growth rate and flow rate was affected by concentration and the relationship between growth rate and N concentration was affected by flow rate such that growth was a linear function of N flux. Thus, N flux proved to be a better predictor of growth rate than water flow rate or N concentration taken alone. Increased N flux during a period of high N concentration increased both the maximum photosynthetic rate and photosynthetic rates at low irradiances of G. tikvahiae and Enteromorpha clathrata. Storage of N taken up during N pulses (relatively short episodes of high N availability) as photosynthetic pigment protein complexes would thus allow macroalgae to fix carbon rapidly to supply carbohydrates necessary for growth during N-limitation and for rapid N uptake during the next N pulse. The effects of nutritional history on NH⁺₄ uptake by Ulva lactuca, Gracilaria tikvahiae and Enteromorpha spp. were investigated. Algae grown at low N fluxes or in N-free medium took up NH⁺₄ much more rapidly than algae grown at high N fluxes. Enteromorpha spp. took up NH⁺₄ more rapidly than the other species. Rapid uptake by algae immediately after collection from the field, after growth at low N fluxes or after growth in N-free medium suggests that N-limited or starved algae in the field can take up pulses of N rapidly (in excess of immediate requirements). G. tikvahiae, Enteromorpha spp., and filva lactuca grew in N-free medium at rates similar to those observed at the high and low N fluxes for 14, 10 and 9 days (respectively), indicating that N taken up during periods of high N availability can support growth in the absence of N. Experimental manipulation of the frequency with which N pulses occurred in the field showed that the frequency with which N pulses occur in nature may be important in regulating the species composition and productivity of macroalgal communities.

No description available.

Thesis (DBA(DoctorateofBusinessAdministration))--University of South Australia, 2004.

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 135-154).

Thesis (M. Phil.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 85-107).

Thesis (M. Phil.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 84-93).