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Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

1. The net annual primary productivity of L, hyperborea has been estimated from biomass increment croppings and biomass: age relationships, The values of 16.5 mt organic matter/ha/year at 3.lm and 8,Omt organic matter/ha/year at 9.1m indicate., the high productivity of this species, 2. Various other growth parameters such as maximum biomass, LAI, net assimilation rate, chlorophyll content and index, and photosynthetic rates have been compared with the data for other communities. 3. An 'in situ' technique, which seems to measure a value close to gross photosynthesis in L, hyperborea, has been used to estimate the photosynthetic capacity of tissues of L. hyperborea at various depths, under the forest canopy, and during the seasonal growth with the following conclusions:- a) Photosynthetic efficiency was found to increase with depth b) The forest canopy had a marked shading effect on the photosynthetic capacity of tissue sections, c) Photosynthesis measured during the season showed that growing lamina tissue was below the compensation point in February, that maximum photosynthesis was in May, and that photosynthesis decreased in the summer. d) The values for daily net photosynthesis compared favourably with estimates of net assimilation rate from biomass studies, 4, Laboratory investigations on photosynthesis gave the following saturation and compensation data:- The new lamina of shallow plants was found to have a higher photosynthetic efficiency than the old lamj.na of shallow plants at low irradiance. The old lamina was found to have a slightly higher photo synthetic efficiency at low irradiance than the lamina of deep growing plants. 5. Respiration rates were measured at various temperatures and the stenothermal nature of the lamina tissue was shown in the RT curve, Lamina tissue was found to have a low optimum temperature for respiration of 9.5°C, The respiration rate of deep-growing plants appeared to be lower than shallow plants. Mannitol was implicated as the primary respiratory substrate and was interconvertible with laminarin; the latter did not appear to be utilised as suggested by Yamaguchi et al. (1966). There appeared to be little heterotrophic uptake and utilisation of exogenously supplied glucose but differences in uptake rates found were found between tissues, that of the stipe and holdfast being greater than the lamina, 6. Young sporophytes maintained in culture showed that low irradiance resulted in a thinner lamina than that found in high light grown plants and light was implicated as an additional factor to wave action in the control of lamina morphology 'in situ'. Deep-growing plants which also had a thinner lamina than shallow plants, had an increased chlorophyll content on a weight basis but not on lamina area basis compared with shallow plants. The increased chlorophyll content was not accommodated by changes in the internal ultrastructure of the chloroplasts, 7. Evidence was presented for a translocation of C14 labelled assimilates from the old lamina to the new lamina and stipe and from the stipe to the lamina. The rate of movement varied from 1.5 to 9cm/h. The mass transfer varied from 0.1.mg mannitol/day from the lamina to the stipe and from 13mg mannitol/day from the stipe to the new lamina, and from 2 to 6mg mannitol/day from the old lamina to the new lamina. These amounts were considered to be capable of supporting observed growth rates of the new lamina from biometric data.

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Call number: LD2668 .T4 1957 A88 / Master of Science

A new approach has been introduced to characterize the epidermal growth factor receptors and their relation to the mechanism of cell growth control using hybrid cells made between human EGF responsive cells and mouse A9 cells incapable of EGF binding. BALBc mice were immunized with human carcinoma A431 cells carrying an extraordinary high number of EGF receptors; antisera were used to identify the human nature of EGF receptors in these hybrid cells. One of the hybrid lines, C2B5, that retains only one human chromosome, an X/7 translocation, and a nearly complete mouse parental genome was used to analyze the relationship of the binding ability and certain post-receptor functions to the cellular mitogenic response. It was shown that the ability to bind, internalize and degrade the ligand and/or its receptor is not sufficient for cells to respond to the mitogen. Spleen cells from mice immunized with A431 cells were fused with mouse myeloma P3NP cells. One of the isolated hybridoma lines, B4G7, secreted a monoclonal antibody of the IgG class which inhibits the binding of ¹²⁵I-EGF to A431 and human fibroblasts, but not of mouse 3T3 cells. This inhibition was partial (65-70%) and Scatchard analysis of the binding data suggested that antibody preferentially interacts with a low affinity class of EGf receptors. The antibody specifically precipitated EGF receptor from radiolabeled cells. This monoclonal antibody was crosslinked to subunit A of toxic ricin through a disulfide bond. The resulting conjugate inhibited protein synthesis of A431 cells at 4 x 10⁻¹¹M and exhibited substantial cell killing. Using this conjugate we isolated a variant of A431 cells, designated C1-B7, with approximately 30 times less EGF binding capacity. Contrary to the parental A431, this variant is resistant to EGF-induced suppression of cell growth and appears to have lost most of the low affinity receptors. The high affinity type EGF receptors retained by the variant are 170,000 Mr and susceptible to EGF-induced phosphorylation, presumably on tyrosine residues. In membrane prepared from this variant, besides the EGF receptor, a low molecular weight component of as yet unknown nature is highly phosphorylated in an EGF-independent manner.

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