M.Sc. (Botany) / Senescence of carnation flowers is accompanied by an increase in the sensitivity of the petals to ethylene. It appears that ethylene sensitivity during normal senescence and under stress conditions is induced by the production of short-chain saturated fatty acids ranging in chain-length from C7-C10 during the early stages. During pollination-induced senescence these acids are synthesized in the styles as a result of wounding and transported to the corolla where they induce an increase in ethylene sensitivity of the petals to ethylene, causing an advancement in the timing of the climacteric peak in ethylene production. It appears that the cell membrane is the site' of action for short-chain fatty acids in their regulation of ethylene sensitivity in plant tissues. These acids cause an increase "in the ability of the tissue to bind ethylene by affecting the physical properties of the cell membranes. Treatment with STS results in a suppression of ethylene sensitivity by stabilizing the cell membranes, thereby decreasing the ability of ethylene to bind to its receptor sites in the cell membranes. Treatment with short-chain fatty acids overrides this stabilizing effect to a great extent by increasing the permeability of cellular membranes and thus the sensitivity of the carnation petal tissue to ethylene.

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The results obtained for the cross-sectional areas of the series of long-chain fatty acids may best be summarized with the aid of Graph 9. This graphical representation of the molecular areas, in Ų , against the chain length (n), of the fatty acid molecules, illustrates variation of the areas with chain length for the series in recrystallized form, and also for selected samples in the zone purified and vacuum distilled forms. On the graph, the limits of variation of the molecular areas have been represented as lines of a length corresponding to twice the standard deviation (2S). This is to give representation that the standard deviation may be positive or negative in relation to the mean. For molecules with n odd and lying between 15 and 19, the molecular area decreases. This may be due to the effect of 3 factorsg (1) A general decrease in lateral translation because of the increasing molecular mass (translational kinetic energy per molecule = ½ mc ⁻²), resulting in closer spacing of molecules. (2) A general, but steady decrease in the angle of tilt of the molecules which thus tend to be held more erect in the condensed film. (3) A general decrease in the precessional motion of the hydrophobic chain groups. For molecules with n odd and between 19 and 23, the molecular areas increase probably due to the steady increase in molecular mass causing the long chains to commence to buckle, tilt or topple in their upper regions. This tilting becomes greater because of the increasing gravitational effect on the heavier molecules which tends to make them assume a flatter posture in relation to the surface. The lower values observed for margaric and nonadecanoic acids, may be due to increasing symmetry in the chain, with corresponding economy in packing in condensed monolayers. This effect may be connected with increasing cylindrical symmetry of the hydrocarbon chain for even values of n. The results of this investigution, incomplete as it is, - serve to indicate what might reasonably be expected to happen in the orientation of these fatty acids in monolayers. Further work, especially on a greater range of acids with even n, is clearly necessary in order to establish the tentative ideas which have been suggested. However, in the present research, work was limited to those acids in the series which were obtainable without undue difficulty or delay, those which would spread readily under the conditions of experiments carried out at 20°C, and those which could be purified relatively easily. The acids below n = 15 in the series were found to be too soluble in aqueous substrates, at operating temperatures of 20°C, to yield reliable evidence with the Langmuir trough technique. The acids above n = 23 were unobtainable commercially and the synthesis of those acids from the lower members in the series presented problems of isolating the required specimens and difficulty in purifying these, which were considered b be beyond the scope of the present research. Summary and conclusion, p. 122.

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The underlying cause was sought for "inactivation", a heat-induced change in the surface of veneer that inhibits diffusion of moisture into the wood. It was demonstrated, by the use of Douglas fir wood, that the formation of an inactivated surface could be prevented by extraction with certain organic solvents, but not with water, either before or after the wood was dried. When the extractable materials were removed, or were originally absent, no specimen examined showed degradation, through the effect of heat, of the potential for forming strong glue bonds. The frequently postulated statement related to formation of ether linkages from hydroxyl groups, in heated wood, was found to be not correct. Although oxidation had been suggested as a contributing factor, inactivated surfaces were prepared in the absence of oxygen in anything but minute amounts. Veneer was collected from Coastal and Interior type Douglas fir trees that exhibited severe, moderate or no susceptibility to the development of inactivation. Representative samples were extracted with simple alkanes and a complete separation of the various components carried out, using the techniques of gas/liquid, paper and thin-layer chromatography. Qualitative variability was found, between and within trees. Strong correlation was found between the formation of an inactivated surface and the presence of saturated fatty acids with carbon-chain lengths in excess of eighteen atoms. The role of long-carbon-chain, saturated fatty acids as the causal agent of inactivation was substantiated by the application of commercially-prepared acids, of various chain lengths, to veneer that had proven insusceptible. When heated, this veneer developed an inactivated surface. A theory was proposed, based on the work described in this thesis, and the information available in the literature, to explain the mechanism of surface modification. It states that removal of some or all of the last molecular layer of water from the wood surface, and the application of heat, permits the saturated long-chain fatty acids to hydrogen-bond with the hydroxyl groups contained in the wood cellulose. The surface of the wood is then shielded by a hydrocarbon layer with very low free surface energy that is not- readily wet-table by the water contained in applied glue. / Forestry, Faculty of / Graduate

The cells of two plants, Coffea arabica and an unknown Mentha species, were grown as suspension cultures in liquid media, in order to analyse and compare the fatty acids and sterols of the cell cultures to those found in the parent plants. The cell growth, the parameters of pH and conductivity of the media, and the composition of the neutral lipid fraction were examined. In the case of the coffee cell cultures, the cell growth and the media pH and conductivity were studied in three different media, two defined and one undefined, while the mint cell cultures were studied in one other defined medium. Both coffee and mint cell cultures were grown in the absence of light (normal cultural conditions) and in the presence of light. The coffee cells showed no differences in growth rate due to variations in media composition. Exposure to light affected neither the growth rate nor initiated chlorophyll formation in the coffee cell cultures, although a distinct green pigmentation formed in the mint cells. A plot of the ionic conductivity of coffee and mint cell suspension cultures was essentially a mirror image of the growth curve of the respective culture. The fatty acids present in the neutral lipid fraction of the cells were studied via gas chromatography, and were compared to the fatty acids found in the seeds and tissues of the parent plants. Palmitate, stearate, oleate, linoleate and linolenate were found in all coffee and mint cell cultures, independent of the composition of the media and of the presence of absence of light. The appearance of short chain fatty acids (less than C-l6) occurred during the dying phases of culture. The fatty acid composition of the coffee cell cultures resembled the analyses of the leaf and stem tissues of the coffee plant rather than the coffee bean. The cell cultures all contained linolenate, not found in the coffee bean, and lacked arachidate, which was present in the bean. In contrast to the coffee cell, the mint cell fatty acids resembled the fatty acid composition of the mint seed rather than the parent plant tissues which contained substantial quantities of the short chain fatty acids (less than C-16). The total fatty acid content of the coffee and mint cell cultures was lower than the seeds of the parent plant, but was comparable to parent plant tissues. A decrease in the total fatty acid content of the neutral lipid fraction of both cultures was noted during the death phase of culture. The total fatty acid content of the coffee cell cultures was not altered by changes in media composition, nor by growth of the cultures in the presence of light. However, the growth of mint cell cultures ln the presence of light had a marked effect on the fatty acid content, which increased approximately four fold in comparison to cultures grown in the dark. The sterol composition of the unsaponifiable lipid found in the extracts of coffee and mint cell cultures was investigated via gas chromatography and thin layer chromatography. The sterols present were compared to those found in the seeds of the parent plants. The sterols found in large concentration in the coffee cells werep -sitosterol, stigmasterol and campesterol, while in the mint cells only ϐ -sitosterol was conspicuous. The predominant sterols found in the seeds of the parent plants and in the plant cell cultures were identical. However, the cell cultures of both coffee and mint contained larger amounts of sterols in their saponified lipid extracts than found in the seeds. Furthermore, in comparison to the seeds, the lipid extracts of the cell cultures contained greater quantities of unesterified sterols. A wide variety of sterols other than desmethyl sterols were located in the seeds and cell cultures, but were not identified as they constituted only a minor portion of the total plant sterols present. A large portion of the unsaponiflables of the coffee bean was characterized as non-steroidal. This non-steroidal material was identified as a mixture of two diterpenold alcohols, cafestoi and kawheol, both known to be major constituents of the unsaponiflables of coffee bean oil. The coffee cell oil unsaponifiables were also found to contain these two diterpenoid alcohols. / Land and Food Systems, Faculty of / Graduate

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