title: Spontaneous action potential initiation and propagation in developing cell segments of Acetabularia mediterranea

authors: Thavarungkul, Panote

abstract: The spontaneous action potentials which occur during the redevelopment of anucleate isolated stalk segments (ISS’s) of the unicellular alga Acetabularia mediterranea have been studied using a novel non-invasive technique. This involved measurement of spatial samples of the time dependent potential in the external medium (sea water) and an inverse transformation to give the current distribution at the cell surface. A detailed description of the method of regularization needed to handle this ill-conditioned inversion problem is presented, along with the results of test experiments to demonstrate its validity.
The initiation region and subsequent propagation (if any) of each action potential was then analysed from the computed transmembrane currents. The results showed that the occurrences of the spontaneous action potentials followed a rhythm which had a period of ~24-30 hours. These action potentials initiated more frequently at the ends of the ISS’s than in the middle region. Contrary to the findings of Novak and Bentrup (1972) in which the cell segments had been maintained in unnatural conditions (a partitioned cuvette with electrical isolation between partitions) which could very well have resulted in perturbation of the cell environment, our results show no firm correlation between the regions of action potential initiation and the site of the redeveloping apex. Generally both propagating and non-propagating action potentials were observed in the same ISS, the ratio of which seems to depend on the length of the cell. The analysed initiation sites and the propagation behaviour of the spontaneous action potentials generated by the ISS’s during the redevelopmental process do not provide any support to the symmetry-breaking role of the propagating action potentials as proposed by Novak and Bentrup.

text: Spontaneous action potential initiation and propagation in developing cell segments of Acetabularia mediterranea The spontaneous action potentials which occur during the redevelopment of anucleate isolated stalk segments (ISS’s) of the unicellular alga Acetabularia mediterranea have been studied using a novel non-invasive technique. This involved measurement of spatial samples of the time dependent potential in the external medium (sea water) and an inverse transformation to give the current distribution at the cell surface. A detailed description of the method of regularization needed to handle this ill-conditioned inversion problem is presented, along with the results of test experiments to demonstrate its validity.
The initiation region and subsequent propagation (if any) of each action potential was then analysed from the computed transmembrane currents. The results showed that the occurrences of the spontaneous action potentials followed a rhythm which had a period of ~24-30 hours. These action potentials initiated more frequently at the ends of the ISS’s than in the middle region. Contrary to the findings of Novak and Bentrup (1972) in which the cell segments had been maintained in unnatural conditions (a partitioned cuvette with electrical isolation between partitions) which could very well have resulted in perturbation of the cell environment, our results show no firm correlation between the regions of action potential initiation and the site of the redeveloping apex. Generally both propagating and non-propagating action potentials were observed in the same ISS, the ratio of which seems to depend on the length of the cell. The analysed initiation sites and the propagation behaviour of the spontaneous action potentials generated by the ISS’s during the redevelopmental process do not provide any support to the symmetry-breaking role of the propagating action potentials as proposed by Novak and Bentrup.

year: 1985

title: Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand

authors: Paul, Wendy J.

subjects: bacillariophyta

abstract: Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.

text: Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.

year: 2012

title: Researching the Process of Auahi Kore for Marae

authors: Masters-Awatere, Bridgette

abstract: • The current report is piece of a qualitative research exploring issues relating the development of Marae Auahi Kore. Such aspects as; factors that aid or impede the process, resources available or required by marae, and people's perceptions of the Auahi Kore brand were explored.

• Interviews were conducted with people from a variety of backgrounds. Research participants included: Marae Trustees, Public Health Workers, Runanga Staff as well as Kaumatua and Kuia. These people were identified as key informants for the current project. A total of 25 people were interviewed during March and April using an open interview schedule.

• Exploration into the Smokefree policies of marae was not pursued within the current project as this was not the focus nor the intent of the research. Project constraints such as time and budget meant there was a limit to what could be undertaken for the current piece of research.

text: Researching the Process of Auahi Kore for Marae • The current report is piece of a qualitative research exploring issues relating the development of Marae Auahi Kore. Such aspects as; factors that aid or impede the process, resources available or required by marae, and people's perceptions of the Auahi Kore brand were explored.

• Interviews were conducted with people from a variety of backgrounds. Research participants included: Marae Trustees, Public Health Workers, Runanga Staff as well as Kaumatua and Kuia. These people were identified as key informants for the current project. A total of 25 people were interviewed during March and April using an open interview schedule.

• Exploration into the Smokefree policies of marae was not pursued within the current project as this was not the focus nor the intent of the research. Project constraints such as time and budget meant there was a limit to what could be undertaken for the current piece of research.

year: 2000