Anthocyanins in selected Proteaceae

[摘要] ENGLISH ABSTRACT:Trials were conducted to follow colour development during the growth season ofthe commercial Leucadendron cultivar 'Siivan' Red', as well as the Protea cultivars'Ivy', 'Carnival' and 'Sylvia'. HPLC analysis showed that pigments responsible forred colour in Leucadendron and Protea cultivars are anthocyanins.Initial extraction of anthocyan ins from freeze-dried and finely groundLeucadendron leaves, using 5% formic acid in methanol, resulted in theprecipitation of gel-like compounds, making the extracts impossible to filter forHPLC. Trials were conducted to determine the optimum extraction solvent andextraction time for anthocyanin quantification in Leucadendron, using 'SafariSunset' (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 addedto freeze dried leaf samples and allowed to extract for one hour. Extracts wereanalysed by reverse-phase HPLC. Extractions with methanol and water yieldedextracts with a high content of pectin-like compounds, making them difficult topurify for HPLC. 80% acetone proved to be the most efficient extraction solvent,yielding the highest anthocyanin concentration, and showing the least amount ofinsoluble compounds. Optimal extraction time was determined for 80% acetone bytesting 1, 6 and 24-hour extractions respectively. Although 6 hour extractionshowed a slightly higher yield, a 1-hour extraction should suffice for quantificationof anthocyanin changes over time, as trends will clearly be evident.'Siivan Red' shoots meeting export quality can generally be harvested from midFebruary to mid April (late summer to autumn). The harvesting period ends as thecolour of the distal leaves forming the flower head change from red to green.Anthocyanin, chlorophyll and carotenoid fluctuations were investigated in 'SiivanRed' during the 2000 growth season. The observed red colour loss is the result ofthe net degradation of anthocyanins and appeared to be correlated to thephenological development of the shoot. Although a positive correlation was notedbetween anthocyanin content and average daily temperature and mean dailysunlight hours, it appears unlikely that they are the causal factors for the observedcolour change. Anthocyanin degradation started during conditions of longexposure to high light intensities and continued during a period of low temperature(autumn), both which are known to favour anthocyanin synthesis rather than itsdegradation. Therefore it appears that colour development in 'Silvan Red' isdevelopmentally regulated.The Leucadendron cultivar 'Safari Sunset' with the same parentage as 'SiivanRed', is noted for its more intense red-purple colouration, which it does not loseduring its development. The more intense colouration of 'Safari Sunset' has beenascribed to the higher total anthocyanin concentration, which was almost doublethat encountered in 'Siivan Red'. 'Safari Sunset' was shown to contain the samemajor types of anthocyanins, and hence the purple colouration (not seen in 'SiivanRed') can not be explained in terms of different types of anthocyanins beingpresent. 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 likelyresponsible for the observed purple colouration. High anthocyanin concentrationshave been noted to buffer against visual changes in colour, which is the mostprobable reason that a colour loss is not observed in 'Safari Sunset'.Colour development of the innermost involucral bracts of three Protea cultivarswas 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 differencesin total anthocyanin concentration.Colour development in 'Carnival' showed a quadratic trend with time, with thehighest rate of anthocyanin synthesis occurring a week prior to harvest. Colourdevelopment in 'Ivy' and 'Sylvia' were shown to be linear with time.As inflorescences are closed during their development and anthocyanin synthesisin the innermost involucral bracts occurred in darkness, light does not appear tohave a major influence on colour development. Temperature did not appear tohave a significant effect on flower colour, as flowers developing later in theseason, when ambient temperatures were lower, showed no significant differencesin anthocyanin concentration to those harvested earlier. Hence, it appears thatcolour development in all three cultivars is developmentally regulated.

[发布机构] Stellenbosch University