The Nature of the White Colour of Petals

Whiteness in flowers has been ascribed to reflection of lightor to the presence of flavones in the tissue. Light reflectionfrom the surface of chrysanthemum petals and the pigment contentof the petals were determined before and after various treatments.After squashing or infiltration of the petals with water, lightreflection was reduced to half or less, whereas flavone contentremained almost unimpaired. Further reductions in light reflectionwere obtained by removing the cuticle. An albino Antirrhinumwas white in colour, yet contained no flavone. These resultsare discussed and it is concluded that whiteness is due to reflectionof light, particularly by the surfaces round air spaces.     

Photocontrol of Growth, and of Anthocyanin and Chlorogenic Acid Production in Cultured Callus Tissues of Haplopappus gracilis

Cultures of dark-grown Haplopappus callus (strain AI) were exposedto continuous blue, green, red, far-red, and white light for33 days at energy levels of approximately 10 J m^-2s^-1. Growthwas suppressed in all but far-red. Blue had the greatest suppressiveeffect, green the least; red and white were about equally effective.Mean cell generation times were increased from 8–8 days(dark control) to 12.5 days in red light and 20.5 days in blue.There was a slight increase in mean wet weight per cell in bluelight but a slight decrease in red, whereas there was almosta twofold increase in mean dry weight per cell in blue and littlechange in red. In contrast, far-red stimulated growth; the meancell generation time was reduced to 6–5 days and therewas little change in wet or dry weight per cell. Anthocyanin synthesis was promoted by all wavebands except far-red.Blue had the greatest effect, then white, red, and green inthat order. In blue light the pigments accumulated rapidly,but only during the early stages of culture. The maximum amountper cell was attained after 7 days and thereafter the valuesdeclined. In red, however, the pigments accumulated relativelyslowly, and the maximum cell content was not attained until22 days; the amount attained was less than half that attainedin blue light. Initially, the ratio of cyanidine-3-glucosideto cyanidine-3-rutinoside exceeded 5.0 in blue light, but theratio fell to almost unity with time. This probably reflecteda rapid initial synthesis of the glucoside accompanied by asteady conversion to the rutinoside. Blue light was also more effective than red in acceleratingchlorogenic acid production. The response to blue light occurredafter the initial rise in anthocyanins and continued for therest of the culture period. The data are discussed in relation to similar high-energy photoresponsesreported for intact systems.     

Production of Anthocyanins, Flavonols, and Chlorogenic Acids by Cultured Callus Tissues of Haplopappus gracilis

A purple-pigmented strain of Haplopappus gracilis callus culturedin vitro produced two anthocyanins, the 3-monoglucoside and3-rutinoside of cyanidine. Light was essential for their production.When dark-grown cultures, irrespective of age, were exposedto light, the anthocyanins accumulated rapidly for about 7 daysand then declined. The 3-monoglucoside accumulated at abouttwice the rate of the 3-rutinoside, and also declined faster.Expressed on a dry-weight basis, production was most efficientin cultures that were approaching stationary phase at exposure.Two flavonol pigments were also produced, the 3-rutinoside and7-monoglucoside of quercetin; these, however, could not be estimatedaccurately. Chlorogenic acid was a prominent constituent of the callus,and consisted of a mixture of the 3- and 5-caffeoyl esters ofquinic acid. Production was enhanced by light though not dependenton it. The two acids were more stable than the anthocyaninsand accumulated over a longer period; they accumulated at similarrates, the 5-caffeoyl ester accounting for 86±3 per centof the total complex. Production was most efficient in culturesexposed to light immediately after inoculation. Anthocyanin production was completely suppressed, and chlorogenicacid production substantially reduced, by inclusion of 2,4-dichlorophenoxyaceticacid, 0.1 mg/1, in the medium.     

Changes in Anthocyanin, Carotenoid, Chlorophyll, and Protein in Developing Florets of the Chrysanthemum

Florets of a purple cultivar (Fandango) of the horticulturalchrysanthemum (Chrysanthemum morifolium Ramat) were removedfrom flower heads at seven stages of opening (from unopenedbud to dying flower) and segregated into different lengths,each of which was analysed. Wet weight per floret increased from 0.25–1 mg in thebud to about 3 mg (tubular florets) or to 20–40 mg (rayflorets) in the fully open flower. Protein decreased from 6per cent of the wet weight in the bud to about 2 per cent inthe open flower. In the ray florets anthocyanin concentrationreached a maximum in the half-open flower and then decreasedsharply, whereas carotenoid and chlorophyll declined continuouslyfrom the bud stage. Almost no anthocyanin was formed by thetubular florets and chlorophyll declined as in the ray florets,but carotenoid concentration increased to a maximum in the half-openflower and then decreased. In another cultivar (Light Bronze Fandango) the content of anthocyaninwas lower and that of carotenoid higher but similar changesin pigment levels were observed except that carotenoid roseto a maximum in the ray florets. In two other cultivars, Redand Cerise Fandango, the anthocyanin content was the same asin Fandango but the carotenoid concentration was the same orabout half that in Light Bronze Fandango respectively.     

Pigment Production by Cultured Florets of Chrysanthemum morifolium

Individual florets (4–5 mm long) of a purple cultivar(Fandango) of the horticultural chrysanthemum (Chrysanthemummorifolium Ramat) were taken from flower buds just prior toopening and cultured in a sterile liquid medium (containinginorganic salts and sucrose) at 15 °C under a 12-h day.For the first 14 days increase in wet weight was exponential.Anthocyanin appeared on the third day and was then synthesizedrapidly. Chlorophyll and carotenoid were present initially:carotenoid levels rose quickly while chlorophyll remained almostconstant. Highest pigment content and most growth were foundwhen the florets were grown on 3 per cent sucrose. However,the highest anthocyanin concentration was found with 4 per centsucrose, the highest carotenoid concentration with 0.6 per centsucrose. No anthocyanin was produced when the florets were grownat 6 or 30 °C; maximum yield was at 15 °C. Most carotenoidwas formed at 30 °C and most chlorophyll was found at 20–5°C. All florets from 1 to 7 mm long could be cultured. Theseresults are discussed in relation to flower colour and pigmentformation in vivo.