The intertidal red algal genus Porphyra is found on rocky shores worldwide. In the Northern Hemisphere the genus is well studied but there is a paucity of data on southern hemisphere Porphyra and even less on New Zealand Porphyra. The species� taxonomy has been undergoing revision since the late 1990�s, when it was discovered that the main species P. columbina and P. lilliputana reported for New Zealand were a combination of several endemic species. These species are found from the low to the high intertidal watermark; hence they are exposed to fluctuating stresses such as desiccation, temperature, high light and UV radiation. Algae have evolved a number of mechanisms to adapt to naturally changing increasing abiotic conditions, such as accumulation of screening pigments and changes in antioxidant metabolism during light stress. For terrestrial plants, polyamines (small aliphatic amines) have been shown to be involved in protecting cells from damage under conditions of stress including UV-B radiation; such mechanisms have yet to be identified in algae.
The overall aim of this study was to determine the importance of cellular processes in shaping the community structure of Porphyra on a wave-exposed shore on the east coast of the South Island, New Zealand. Porphyra distribution and community structure was assessed by regular monthly monitoring of presence and absence of Porphyra along four transect lines at the site. Enviromnental information was recorded to determine the effects of temperature, light, UV radiation, humidity and wind on Porphyra�s spatial and temporal distribution. Regular tissue samples were taken for species identification by the application of primers, which were specifically designed during this study. P. cinnamomea and Porphyra spec. "ROS 54" were identified as dominant species present almost throughout the year with a pronounced maximum in presence during late winter and spring, and some weeks of absence during April or May. The two dominant species were recorded from the low to the high intertidal shore, but the mid intertidal was identified as the preferred habitat. Other species that were found were rare and only present for a few months in a very restricted area. It was hypothesised that free radical generation and antioxidant metabolism are associated with desiccation tolerance in Porphyra. An attempt was made to investigate the impact of desiccation stress on Porphyra. The extraction process of antioxidants was problematic and no reproducible results could be obtained. It was attempted to investigate the spatial distribution of spores and conchocelis of different Porphyra species in the field, and determine if those found at Brighton Beach are species-specific in their morphology. This indicated that the two main Porphyra species at Brighton Beach not only prefer to occupy the same habitat but that they also have a morphologically similar conchocelis phase.
Mechanisms on a cellular level such as polyamine metabolism affected by environmental (abiotic) stresses are related to the alga�s ability to adapt to stress and therefore can have an effect on Porphyra�s distribution along the shore and its presence throughout the year. The depletion of the ozone layer has become an important issue as the effects of increased UV radiation on the environment, especially the intertidal habitat, are revealed. Marine macrophytes possess the main three. polyamines: putrescine, spermidine and spermine of varying levels. For the few species studied, Rhodophyta generally contain higher levels of polyamines than Chlorophyta, while polyamine levels for the one heterokontophyte analysed were between Chlorophyta and Rhodophyta. Levels of the three most common polyamines (putrescine, spermidine, spermine) were determined in P. cinnamomea under controlled UV exposure. Tissue discs were exposed to visible light (PAR), PAR and UV-A or PAR, UV-A and UV-B radiation. Discs exposed to PAR and PAR and UV-A showed little change in polyamine levels over a six day trial period, while discs exposed to PAR, UV-A and UV-B showed a significant increase in free, bound soluble and bound insoluble polyamines over the same period of time. Correspondingly levels of ADC and ODC, two enzymes involved in polyamine synthesis, were measured. ODC levels changed little while ADC levels increased significantly during UV-B treatment, indicating that under UV-B stress polyamines are mainly synthesized via the ADC pathway. The experimental set-up and process of this study has not been applied in macroalgal polyamine research and results obtained are the first indication that increased levels of polyamines are involved in protection and/or protection mechanisms in macrophytic algae to prevent UV-B damage.
| Identifer | oai:union.ndltd.org:ADTP/202521 |
| Date | January 2007 |
| Creators | Schweikert, Katja, n/a |
| Publisher | University of Otago. Department of Botany |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Katja Schweikert |
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