Browsing by Author "Schmeisser, Michael"
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- ItemAnthocyanins in selected Proteaceae(Stellenbosch : Stellenbosch University, 2002-12) Schmeisser, Michael; Jacobs, G.; Holcroft, D. M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.ENGLISH ABSTRACT: Trials were conducted to follow colour development during the growth season of the commercial Leucadendron cultivar 'Siivan' Red', as well as the Protea cultivars 'Ivy', 'Carnival' and 'Sylvia'. HPLC analysis showed that pigments responsible for red colour in Leucadendron and Protea cultivars are anthocyanins. Initial extraction of anthocyan ins from freeze-dried and finely ground Leucadendron leaves, using 5% formic acid in methanol, resulted in the precipitation of gel-like compounds, making the extracts impossible to filter for HPLC. Trials were conducted to determine the optimum extraction solvent and extraction time for anthocyanin quantification in Leucadendron, using 'Safari Sunset' (Leucadendron sa/ignurn x L. /aureo/urn) as reference material. Acetone, 80% acetone, 5% formic acid in water and 5% formic acid in methanol were added to freeze dried leaf samples and allowed to extract for one hour. Extracts were analysed by reverse-phase HPLC. Extractions with methanol and water yielded extracts with a high content of pectin-like compounds, making them difficult to purify for HPLC. 80% acetone proved to be the most efficient extraction solvent, yielding the highest anthocyanin concentration, and showing the least amount of insoluble compounds. Optimal extraction time was determined for 80% acetone by testing 1, 6 and 24-hour extractions respectively. Although 6 hour extraction showed a slightly higher yield, a 1-hour extraction should suffice for quantification of anthocyanin changes over time, as trends will clearly be evident. 'Siivan Red' shoots meeting export quality can generally be harvested from mid February to mid April (late summer to autumn). The harvesting period ends as the colour of the distal leaves forming the flower head change from red to green. Anthocyanin, chlorophyll and carotenoid fluctuations were investigated in 'Siivan Red' during the 2000 growth season. The observed red colour loss is the result of the net degradation of anthocyanins and appeared to be correlated to the phenological development of the shoot. Although a positive correlation was noted between anthocyanin content and average daily temperature and mean daily sunlight hours, it appears unlikely that they are the causal factors for the observed colour change. Anthocyanin degradation started during conditions of long exposure to high light intensities and continued during a period of low temperature (autumn), both which are known to favour anthocyanin synthesis rather than its degradation. Therefore it appears that colour development in 'Silvan Red' is developmentally regulated. The Leucadendron cultivar 'Safari Sunset' with the same parentage as 'Siivan Red', is noted for its more intense red-purple colouration, which it does not lose during its development. The more intense colouration of 'Safari Sunset' has been ascribed to the higher total anthocyanin concentration, which was almost double that encountered in 'Siivan Red'. 'Safari Sunset' was shown to contain the same major types of anthocyanins, and hence the purple colouration (not seen in 'Siivan Red') can not be explained in terms of different types of anthocyanins being present. However, the ratio between the two major anthocyanins present in both 'Safari Sunset' and 'Siivan Red' were significantly different in that 'Safari Sunset' showed a considerably higher concentration of peak 1, which is most likely responsible for the observed purple colouration. High anthocyanin concentrations have been noted to buffer against visual changes in colour, which is the most probable reason that a colour loss is not observed in 'Safari Sunset'. Colour development of the innermost involucral bracts of three Protea cultivars was followed from an initially selected inflorescence size to commercial harvest (when flowers have opened slightly). 'Ivy', 'Carnival' and 'Sylvia' show a light pink, dark pink and red colouration respectively, which has been ascribed to differences in total anthocyanin concentration. Colour development in 'Carnival' showed a quadratic trend with time, with the highest rate of anthocyanin synthesis occurring a week prior to harvest. Colour development in 'Ivy' and 'Sylvia' were shown to be linear with time. As inflorescences are closed during their development and anthocyanin synthesis in the innermost involucral bracts occurred in darkness, light does not appear to have a major influence on colour development. Temperature did not appear to have a significant effect on flower colour, as flowers developing later in the season, when ambient temperatures were lower, showed no significant differences in anthocyanin concentration to those harvested earlier. Hence, it appears that colour development in all three cultivars is developmentally regulated.
- ItemColour dynamics in Leucadendron(Stellenbosch : University of Stellenbosch, 2010-12) Schmeisser, Michael; Steyn, Willem J.; Jacobs, G.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Horticultural Science.ENGLISH ABSTRACT: The bright colouration of involucral leaves in Leucadendron is unfortunately transient in nature. Undesirable colour changes render this cut flower unmarketable, resulting in a considerable loss of profit. A deeper understanding of the mechanism leading to colour change is needed to form the framework on which future manipulation strategies can be built. Yellow Leucadendron possess the ability to degreen and regreen naturally, a phenomenon linked to the controlled degradation of chlorophyll and the lesser degradation of carotenoids, which then impart the yellow colour. This colour change is directly linked to the development of the inflorescence. Involucral leaves degreen towards anthesis and are entirely yellow at full bloom. They begin to regreen again when the last florets on the cone have wilted. Deconing before flowering completely inhibits the colour change. Deconing at full bloom, results in leaves regreening sooner. Therefore the inflorescence appears to be the origin of the cue for colour change. Any factor that expedites the death of the florets, results in sooner regreening of involucral leaves. Ultra-structurally, the degreening and regreening resulted from a transdifferentiation of mature chloroplasts to gerontoplast-like plastids, which upon regreening completely redifferentiated into fully functional chloroplasts. In the red Leucadendron cultivar Safari Sunset, the photosynthetic pigment degradation pattern is identical to that of yellow cultivars. However, colour expression is complexed by the presence of anthocyanins. Anthocyanin concentration was shown to be directly related to the opening of the flower head rather than to the phenological development of the inflorescence. With opening, the previously shaded inner involucral leaf surfaces are exposed to higher levels of irradiance and respond by turning red, presumably for photoprotection. Similar to yellow cultivars, any factor leading to the death of the florets before flowering, not only prevents the degreening of involucral leaves, but also prevents the opening of the flower head and therefore the associated change in anthocyanin levels. The ecological significance of regreening was also investigated. What does a female Leucadendron plant stand to gain by regreening rather than discarding the involucral leaves? Regreened involucral leaves were shown not to play a significant role in providing photosynthates for the developing cone. Although the presence of regreened involucral leaves were shown to provide protection against high irradiance and radiant heating of the cone, they were not essential to ensure survival of the cone. The small floral bracts were shown to be very capable of adaptation. The most plausible reason for regreening is therefore assumed to be based on a cost-benefit relationship. As most Leucadendron are adapted to grow on very nutrient poor soils, the question should maybe be rephrased. Why waste valuable resources? Sclerophyllous leaves, like the involucral leaves, are costly to make and therefore reusing, rather than discarding them does seem a sensible strategy for survival.