title: Quantitative chemical indicators to assess the gradation of compression wood

authors: Nanayakkara, Bernadette

subjects: chemistry of compression wood

abstract: A chemistry-based parameter has been sought for determining the gradation of compression wood (CW), i.e., the severity, in tissues of Pinus radiata wood. Fluorescence microscopy was the reference for characterisation of the tissues containing CW. The collected material contained CW of varying severity, beginning with normal wood (NW containing no CW), continuing with material with some features of CW (CW of mild severity, MCW) and ending up with a material with pronounced features of CW (CW of high severity, SCW). Matching opposite wood (OW) was also included in the study. The chemical analyses included lignin determination, sugar analysis in the acid hydrolysate, thioacidolysis, 31P-NMR spectroscopic analysis and steric exclusion chromatography of thioacidolysis products. As the severity of CW changed progressively from NW through MCW to SCW, all chemical parameters changed concurrently. In particular, levels of galactose and lignin increased, while those of glucose and mannose decreased. The amounts of p-hydroxyphenyl β-ethers released by chemical degradation and uncondensed p-hydroxyphenyl C-9 units also increased at elevated CW severity levels. The amounts of galactose and the p-hydroxyphenyl content of the lignin correlated linearly with lignin for CW samples. The chemical differences between CW and OW in the stem, branch and seedling were similar, i.e., they are independent of the morphological origin of the sample. Parameters based on the p-hydroxyphenyl unit content appear the most suitable chemical indicators of CW severity, as they are least sensitive to the sample's morphological origin and their response to CW severity is high.

text: Quantitative chemical indicators to assess the gradation of compression wood A chemistry-based parameter has been sought for determining the gradation of compression wood (CW), i.e., the severity, in tissues of Pinus radiata wood. Fluorescence microscopy was the reference for characterisation of the tissues containing CW. The collected material contained CW of varying severity, beginning with normal wood (NW containing no CW), continuing with material with some features of CW (CW of mild severity, MCW) and ending up with a material with pronounced features of CW (CW of high severity, SCW). Matching opposite wood (OW) was also included in the study. The chemical analyses included lignin determination, sugar analysis in the acid hydrolysate, thioacidolysis, 31P-NMR spectroscopic analysis and steric exclusion chromatography of thioacidolysis products. As the severity of CW changed progressively from NW through MCW to SCW, all chemical parameters changed concurrently. In particular, levels of galactose and lignin increased, while those of glucose and mannose decreased. The amounts of p-hydroxyphenyl β-ethers released by chemical degradation and uncondensed p-hydroxyphenyl C-9 units also increased at elevated CW severity levels. The amounts of galactose and the p-hydroxyphenyl content of the lignin correlated linearly with lignin for CW samples. The chemical differences between CW and OW in the stem, branch and seedling were similar, i.e., they are independent of the morphological origin of the sample. Parameters based on the p-hydroxyphenyl unit content appear the most suitable chemical indicators of CW severity, as they are least sensitive to the sample's morphological origin and their response to CW severity is high.

year: 2009-07

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: Maori & Psychology Research Unit annual report 2006

authors: Rua, Mohi

subjects: Maori and Psychology Research Unit

abstract: Annual report of the Maori and Psychology Research Unit (MPRU) 2006. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

text: Maori & Psychology Research Unit annual report 2006 Annual report of the Maori and Psychology Research Unit (MPRU) 2006. The unit was established in August of 1997. The unit is designed to provide a catalyst and support network for enhancing research concerning the psychological needs, aspirations, and priorities of Maori people. The MPRU is well situated to draw together skilled and experienced interdisciplinary research groups by networking and establishing working relationships with staff and students within the Faculty of Arts and Social Sciences, the University, and the wider community.

year: 2006