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Journal of Experimental Botany, Vol. 35, No. 160, pp. 1656-1662, November 1984 Flower Colour Changes in Lantana camara H. Y. MOHAN RAM AND GITA MATHUR Department of Botany, University of Delhi, Delhi-l10007, India Received 4 April 1984 ABSTRACT Lantana camara flowers undergo colour change subsequent tq anthesis. In the colour variant selected for the present study, pink buds, yellow newly-opened flowers and ageing orange, scarlet and magenta flowers are found in the same inflorescence. The flower pigments were chemically analysed and identified as delphmidin monoglucoside and fJ-carotene. Thrips are regular pollinators of LantafUI under Delhi conditions. Pollination was identified as the trigger for rapid anthocyanin synthesis. Even the presence of one pollen grain on the stigma of a yellow flower was sufficient to cause colour change. Injection of a suspension of pollen into flowers opened in vitro caused pigment changes. An extract of Lantana pollen was also able to simulate the effect of pollination, suggesting the involvement of a pollen factor. The post-pollination shift in petal colouration is caused by the masking of carotenoids by differential amounts of anthocyanin. As thrips are attracted to only yellow flowers, chromatic changes playa role in conserving pollinator energy. Key words: Anthecology; Floral pigments; Lantana camara; Pollination. INTRODUCTION Colour, size, form and number of floral parts constitute the major visual attractants for pollinators. In recent years there has been a resurgence of interest in the study of floral colouration and its significance in anthecology (Kevan, 1978). Polymorphism in flower colour has been correlated with pollinator partitioning in Cirsium palustre (Magford, 1974a, b), Leavenworthia crassa (Lloyd, 1969) and Raphanus raphanistrum (Kay, 1976). Flower colour polymorphism may also be influenced by edaphic factors (Horovitz, 1976; Frias, Godoy, Iturra, Koref-Santibanez, Navarro, Pachew, and Stebbins, 1975; Dakshini, Roonwal, and Gupta, 1982). Flowers of several plants undergo change in colour after opening. There are numerous colour forms in Lantana camara, which according to Stirton (1978), is not a single variable species but is a species aggregate with a few parental species and their numerous hybrid derivatives. Howard (1970) and Barrows (1976) had reported post-anthesis flower colour changes in Lantana camara. In a short communication we have explained the significance of petal colour changes in the pollination of Lantana by thrips (Mathur and Mohan Ram, 1978). In this paper the cause of flower colour change has been examined and the nature and biogenesis of floral pigments and their quantitative changes at different stages of flower development have been presented. at National Chung Hsing University Library on April 12, 2014 http://jxb.oxfordjournals.org/ Downloaded from

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Page 1: Flower Colour Changes in Lantana camara

Journal of Experimental Botany, Vol. 35, No. 160, pp. 1656-1662, November 1984

Flower Colour Changes in Lantana camara

H. Y. MOHAN RAM AND GITA MATHUR

Department of Botany, University of Delhi, Delhi-l10007, India

Received 4 April 1984

ABSTRACTLantana camara flowers undergo colour change subsequent tq anthesis. In the colour variant selectedfor the present study, pink buds, yellow newly-opened flowers and ageing orange, scarlet and magentaflowers are found in the same inflorescence. The flower pigments were chemically analysed andidentified as delphmidin monoglucoside and fJ-carotene.

Thrips are regular pollinators of LantafUI under Delhi conditions. Pollination was identified asthe trigger for rapid anthocyanin synthesis. Even the presence of one pollen grain on the stigma ofa yellow flower was sufficient to cause colour change. Injection of a suspension of pollen into flowersopened in vitro caused pigment changes. An extract of Lantana pollen was also able to simulatethe effect of pollination, suggesting the involvement of a pollen factor. The post-pollination shiftin petal colouration is caused by the masking of carotenoids by differential amounts of anthocyanin.As thrips are attracted to only yellow flowers, chromatic changes playa role in conserving pollinatorenergy.

Key words: Anthecology; Floral pigments; Lantana camara; Pollination.

INTRODUCTIONColour, size, form and number of floral parts constitute the major visual attractants forpollinators. In recent years there has been a resurgence of interest in the study of floralcolouration and its significance in anthecology (Kevan, 1978). Polymorphism in flowercolour has been correlated with pollinator partitioning in Cirsium palustre (Magford,1974a, b), Leavenworthia crassa (Lloyd, 1969) and Raphanus raphanistrum (Kay, 1976).Flower colour polymorphism may also be influenced by edaphic factors (Horovitz, 1976;Frias, Godoy, Iturra, Koref-Santibanez, Navarro, Pachew, and Stebbins, 1975; Dakshini,Roonwal, and Gupta, 1982).

Flowers of several plants undergo change in colour after opening. There are numerouscolour forms in Lantana camara, which according to Stirton (1978), is not a single variablespecies but is a species aggregate with a few parental species and their numerous hybridderivatives.

Howard (1970) and Barrows (1976) had reported post-anthesis flower colour changes inLantana camara.

In a short communication we have explained the significance of petal colour changes inthe pollination of Lantana by thrips (Mathur and Mohan Ram, 1978). In this paper thecause of flower colour change has been examined and the nature and biogenesis of floralpigments and their quantitative changes at different stages of flower development have beenpresented.

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MA TERIALS AND METHODSThe colour variant of Lantana selected for the present study occurs abundantly as a weed in the DelhiUniversity Campus and shows well-defined colour changes. Each inflorescence bears 36-38 bracteate,sessile flowers (15-17 rnm long), spirally arranged on a condensed oval axis. The apices of the youngflower buds are pink. The freshly opened flowers are yellow, which become orange after 20 h. There is afurther shift in colour to scarlet within 7-8 h followed by magenta after 26 h. All flowers have a deepercolouration around the mouth of the corolla tube.

The buds/flowers have been classified into six distinctly recognizable stages of development asdetailed below. These stages have been taken as standards for reference in the text (Fig. I).

>--1

lmm

II 111YELLOW

IVORANGE

VSCARLET

VIMAGENTA

FIG. I. Stages of flower development.

Stage I: Buds 3-4 mm long, spirally arranged in the centre of the inflorescence, tips light pink, 2-3 dbefore anthesis.Stage II: Buds 8-10 mm long, tips bright pink, I d prior to opening.Stage II I: Open flowers with yellow corolla. Mouth of corolla buttercup yellow No. 5 (seeHorticultural Colour Charts, London), lobes canary yellow No. 2/2. Nine hours after anthesis, mouthIndian yellow No. 6/1, lobes Indian yellow No. 6/2. Stigmatic exudate abundant. Copious amount ofnectar present at the base of the ovary. Flowers receptive for pollination.Stage IV.' Flowers orange-coloured. Mouth of corolla orange No. 12, lobes orpiment orange No. 10/2.Stage V: Flowers scarlet, outer to stage IV flowers. Petals fresh and turgid, mouth of corolla scarletNo. 19/1, lobes crimson No. 22/1.Stage VI: Magenta (No. 27/1) flowers with shrivelled corollas surrounding stage V flowers.

Preliminary studies showed that the two major groups of pigments are carotenoids (yellow) andanthocyanins (red). For characterization of the chemical nature of anthocyanins, the pollinated flowersof Lantana were extracted in methanol-HCI (1%). The aglycone and sugar moieties were separated byacid hydrolysis, refluxing under reduced pressure, solvent separation and 2-D chromatography. Theaglycone was identifed by cochromatography with standards, spectrophotometry and RF values invarious solvent systems (Harhorne, 1958a, b; Jain, 1973; Harborne, Mabry, and Mabry, 1975; Mathur,1976, 1983). The sugar moiety was characterized by chromatography with standard sugar samples.The monoglucoside nature of the anthocyanin was determined by chromatography with knownanthocyanin (Jain, 1973) and by RF values in standard solvent systems (Harhorne, 1958a). Carotenoidswere extracted from yellow flowers, purified, saponified and analysed by thin layer chromatography.

Because of difficulties in extracting and isolating anthocyanins from carotenoid-rich yellow flowersand carotenoids from scarlet and magenta flowers containing anthocyanins, separation of purepigments was incomplete. To overcome the difficulties the procedure of extraction was modified asfollows. Five grams (fresh weight) of bud/flower corollas at various stages of development wereextracted in methanol followed by extraction in methanol-HCl containing ascorbic acid. Carotenoidswere isolated from the former extract and anthocyanins from the latter.

A quantitative estimation of the anthocyanins and carotenoids was made by determining a.D.values at 535 nm and 430 nm respectively, using a Systronics 20 spectrophotometer.

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1658 Mohan Ram and Mathur-Flower Colour Changes in Lantana

Bud corollas (Stage II) and yellow flower corollas (Stage lID were excised and planted on autoclavedplain (0-8%) agar medium in Petri plates (7·5 em in diameter). The sequence ofcolour changes occurringin them was noted.

RESUL TS

Characterization of anthocyanin and carotenoids

The R F values for Lantana petal anthocyanidin were recorded to be 0·30 in Forestal (aceticacid: HCI: water; 5: 3: 2) and 0·42 in SAW (butanol: acetic acid: water; 4: I : 5; upper layer).These values indicate the aglycone to be delphinidin (Harborne, 1958a, 1967).

To confinn further that the aglycone was delphinidin, a complete visible absorption wasrecorded for the purified aglycone on a spectrophotometer from 390 nm to 610 nm (at 5 nmintervals). A peak was noted around 540-545 nm, which coincided with the peak ofabsorption established for delphinidin (Harborne, 1958a, 1967; Harborne et al., 1975).

Extracts from Lantana flowers at six stages ofdevelopment were cochromatographed. Themajor spots developed after a 14 h descending run in SAW had the same level (same R F

values) indicating that the same anthocyanin was present at all the stages. The sugar moietyof anthocyanin was identified as glucose by cochromatography with standard sugars (R F

value for Lantana sugar moiety was 0·451 and for glucose 0-452 in SAW). The R F values ofunhydrolysed anthocyanin in butanol-Hel and SAW were 0·11 and 0·255 indicating that itwas delphinidin monoglucoside (Harborne, 1958a}

The purified carotenoid extract of Lantana flowers, subjected to thin layer chromato­graphy using 11 solvent systems yielded 14-16 spots. Cochromatography with authenticf3-earotene revealed the major component to be f3-earotene. The minor components were notanalysed.

Quantitative changes in pigments during flower development

As no other pigments were identified in the extracts, it was considered necessary toestimate the amounts of anthocyanin and f3-carotene in the corollas at different stages offlower development.

The average fresh and dry weights ofcorollas at six stages of flower development togetherwith O.D. values for anthocyanin and carotenoids are presented in Fig. 2.

A peak of carotenoid synthesis (97·43%) was recorded between stages I and II. Theincrease in carotenoids was about 13% in the next stage, followed by 7% from stage III to IV.The total amount ofcarotenoids continued to remain steady until stage V, after which a 17%decrease was recorded. Thus carotenoid synthesis was highest before anthesis and continuedat a low rate until stage IV, followed by complete cessation after stage IV and degradationafter stage V.

From stage I to II the increase in O.D. for anthocyanins was about 18% and from stage IIto III it was about 9%. Between stage III and IV a substantial stimulation in anthocyaninproduction (86%) was noted. A fall in the total amount of anthocyanins occurred afterstage V, accompanied by withering of the corolla.

The increase in fresh and dry weights was rapid between stages I and III followed by a slowincrease up to stage V. Subsequently the fresh weight showed a sudden fall. The dry weight,however, registered a negligible increase.

Role of pollination in petal colour change

In Lantana flowers, pollination under field conditions occurs just after anthesis when thepetal colour is yellow, corresponding to stage III of flower development. As the colourchanges to orange subsequently, it was logical to examine the relation between pollination

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1.6

lS

1.4

13

12

11>t: 1.0(/)

z Q9lJJ0

Q8....J<t OJui= Q6Q.

0Q5

0.4

0.3

0.2

0.1

II III IV V VI

STAGES

Mohan Ram and Mathur-Flower Colour Changes in Lantana 1659

160

150

140

130

120

110

100~CII

90 E

80~Cl

70 W60~

50

40

30

20

10

FIG. 2. Fresh and dry weights (data represent mean of 10 bud/flower corollas of each stage) and quantityof purified pigments (based on three determinations) at six stages of flower developmenL 0.0. was

measured at 535 nm for anthocyanins and at 430 nrn for carotenoids.

and petal colour change and to establish whether this is a mere coincidence or whether thereis a cause-effect relationship.

Colour change in yellow flowers (Stage III) collected between 09.00 hand 10.00 h fromexperimental bushes was studied by implanting corollas alongside their respective pistils onautoclaved plain agar ((}8%) in Petri plates and kept covered. After 2 d about 65% of thecorollas had changed their colour to scarlet whilst the remainder had not. A microscopicexamination of the stigmas showed that the pollinated ones were identified with the corollasthat had become scarlet, whereas unpollinated ones belonged to flowers whose corollas hadnot changed colour. In one case, there was a single pollen grain on the stigma and in anotheronly four, although their corresponding corollas had shown colour change. The remainingstigmas had 55-200 pollen grains each. From these data it may be inferred that pollinationis the trigger for the processes that lead to chromatic alterations in the corolla and that eventhe presence of a single pollen grain on the stigma is sufficient to initiate them. Interestingly,the intensity ofcolouration does not depend on the number of pollen grains deposited on thestigma

Excised buds of stage II that subsequently opened in Petri plates containing agar,remained yellow even after 6 d. Their stigmas showed no pollen grains indicating that lack ofpollination prevented chromatic change.

In vitro pollination: Another experiment was set up to examine whether flower colourchange can be initiated by in vitro pollination. For this, entire inflorescences bearing stage IIflower buds in the periphery were planted in agar plates. As the buds opened, they wereinjected with a suspension of pollen grains prepared in Brewbaker and Kwack's medium(Brewbaker and Kwack, 1963) by means of a syringe inserted through the mouth of the

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corolla. 0·5 cm3 of the medium contained pollen from 20 anthers collected from freshlyopened flowers of the same colour variant of Lantana. Flowers injected with the mediumwithout the pollen served as controls. Scarlet colouration developed in the flowers thatreceived pollen suspension after 2 d, whereas the controls remained yellow. This findingconfirms that both natural and artificial pollination can induce petal colour change.

Effect ofpollen extract: 45 to 50 anthers collected from freshly opened flowers were put in1·0 em3 of Brewbaker and Kwack's medium and crushed with a glass homogenizer. Thehomogenate was filtered and injected into newly-opened flowers in inflorescences planted onagar. The control flowers received the plain medium. Development of scarlet colouration inthe petals in response to the pollen extract suggested that some substances released by pollenconstitute the trigger for chromatic alteration.

Intensity of colour development: It was important to find out whether the duration ofcontact between the pollinated stigma and the corolla influences the intensity of colourdevelopment. To verify this, corollas of freshly opened flowers were excised from the fieldfrom 06·00 h to 18·00 h at 2 h intervals. Immediately after excision the corollas were plantedon agar plates and kept in the culture room. After 48 h the colouration of the corolla in eachset was noted. Corollas collected at 06{)() hand 08'00 h remained yellow; these were fromunpollinated flowers. A light shade of orange-scarlet was observed in the petals excised at10·00 h and an increasingly deeper colouration was noted in the collections made thereafterup to 18·00 h. This study indicated that whereas pollination was the trigger for induction ofcolour change, the intensity of colour development depended on the length of the time thecorolla remained attached to a pollinated flower.

To ascertain whether or not plant hormones are able to simulate the effects of pollination,the corollas of unpollinated flowers (stage II) were planted on (}5% agar containing6-benzylamino purine (BAP) or gibberellic acid (GA 3 ) or indoleacetic acid (IAA) each at10- 7,10- 6,10- 3 and 10- 4 mol dm- 3 . However, none of these hormones was able to causea shift in petal colour at any of the concentrations tested.

DISCUSSION

The main aim of the present work was to establish the basis of flower colour change inLantana camara and to identify the chemical nature and estimate the quantity of pigments.

The anthocyanin of Lantana flowers has been identified as delphinidin monoglucoside andthe major carotenoid as p-<.:arotene. There is no qualitative change in these two pigments,although their relative ratio is altered during development

In the first two stages offlower development, the amount ofcarotenoids is higher than thatofanthocyanin. Stage III represents the peak ofcarotenoid synthesis. A spurt in anthocyaninproduction occurs after pollination. The shift in colour from orange to scarlet and magentais brought about by higher anthocyanin content relative to carotenoids.

Harborne (1976) has explained that in most ornamentals, varieties containing mixtures ofanthocyanin types are as common as those having single pigments. Flowers with mixtures ofthe expected intermediate shades are to be found in Verbena hybrida, Hyacinthus orientalis,Lathyrus odoratus and Streptocarpus hybrida.

In the colour variant of Lantana camara chosen for the present study, the anthocyanin isthe same but its varying proportions in relation to carotenoids accounts for the differentshades. It would be interesting to carry out further investigations on the nature of the majorfloral pigments in the other colour variants of Lantana.

The upland cotton flowers change their colour from cream-yellow at anthesis towatermelon-red the next day (McGregor, 1976). Chhabra and Singh (1978) have noted thatthe newly opened flowers of Gossypium hirsutum var. J. 34 are yellow and that anthocyanin is

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present only after fertilization. At the abscission stage, the concentration of pigment becomesintense. These workers have suggested that there is a relationship between loss of moisturecontent of petal tissues and increase in anthocyanin formation and that sugars and ABAplaya role in these processes. The nature of the trigger for petal colour change in cotton hasnot been characterized.

Arditti, Flick, and Jeffrey (1971) have shown that the application of ABA to unpollinatedflowers of Cymbidium enhances anthocyanin formation in the sepals, petals, columns andlabella, typically noted in pollinated flowers. In response to NAA +ABA, the otherpost-pollination responses are nearly comparable to those in pollinated flowers butanthocyanin content is lower than in the flowers treated with ABA alone. In Lantana BAP,GA 3 or IAA were unable to replace the pollination trigger for petal colour change.

Wainwright (1978) has observed that the flowers of Lupinus arizonicus and L. sparsijfarusbear a yellowish-white banner spot which changes to deep purplish red with pollination.Insects avoid visiting flowers with the latter condition. Wainwright believes that the changein the spot colour is not a response to fertilization, pollen tube growth or pollengermination. Manipulation of the stigma, removal of all the pollen from the stigma or totalexcision of the stigma one day after anthesis induce the spot change. This work is similar tothe situation in Lantana and Wainwright seems to have missed the significance of pollenfactors.

The present work has established that pollination is the trigger for petal colour change. Asthe pollen extract is also able to simulate the pollination effect, it may be speculated that thepollen releases a 'factor' which moves from the pistil to the petals to stimulate anthocyaninproduction. The chemical nature of the pollen factor remains to be established. Thereis recent evidence that in the pollen-stigma recognition phenomenon a saccharide and alectin moiety are involved (Sharma and Shivanna, 1983). Whether induction of colourchange is a similar phenomenon also requires further investigation. The phenomenon ofpost-pollination colour change which provides an advantage in regulating the visitations bypollinators has been noted in several other plants but the mechanism involved has rarelybeen examined.

Thrips (Haplothrips tenuipennis and Thrips hawiiensis) are the regular pollinators ofLantana flowers under Delhi conditions and they visit only yellow flowers, avoiding flowersof other colours on the same inflorescence (Mathur and Mohan Ram, 1978). This findingemphasizes the significance of post-anthesis colour change in the conservation of pollinatorenergy. The mechanism of pollination and the colour preferences exhibited by thrips will bediscussed in another paper.

LITERATURE CITEDARDITTI, J., FLICK, B., and JEFFREY, D., 1971. Post-pollination phenomenon in orchid flowers. II. New

Phytalagist,70, 333-41.BARROWS, E. M., 1976. Nectar robbing and pollination of Lantana camara (Verbenaceae). Biotropica,

8(2), 132-5.BREWBAKER, J. L., and KWACK, B. H., 1963. The essential role of calcium ion in pollen germination

and pollen tube growth. American Journal of Botany, SO, 859-65.CHHABRA, NEELAM, and SINGH, O. S., 1978. Factors affecting anthocyanin synthesis in cotton flowers.

In Physiology ofsexual reproduction in flowering plants. Eds. C. P. Malik, A. K. Srivastava, N. C.Bhattacharya and Rattan Singh. Kalyani Publishers, New Delhi, India. Pp. 136-41.

DAKSHINI, K. M. M., ROONWAL, G. S., and GUPTA, S. K., 1982. Heavy metal accumulation byVernonia cinerea (L.) Less. Asteraceae. Journal of Geochemical Exploration, 16, 235-8.

FRIAS, D., GODOY, R., lTURRA, P., KOREF-SAN1lBANEZ, S., NAVARRO, J., PACHEW, N., and STEBBINS,G. L., 1975. Polymorphism and Chilen population of Eschscholtzia californica. Plant Systematicsand Evolution, 123, 185-98.

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HARBORNE, 1. B., 1958a. The chromatographic identification of anthocyanin pigments. Journal ofChromatography, 1, 473-88.

--1958b. Spectral methods of characterizing anthocyanins. Biochemical Journal, 70, 22-8.--1967. Comparative biochemistry of the flavonoids. Academic Press, London and New York.--1976. Function offlavonoids in plants. In Chemistry and biochemistry ofplant pigments. Volume 1.

Second Edition. Ed. T. W. Goodwin. Academic Press, London and New York. Pp. 736-79.--MABRY, T. J., and MABRY, H., (Eds.). 1975. Theflavonoids. Chapman and Hall, London.HOROVITZ, A., 1976. Edaphic factors and flower colour distribution in Anemoneae (Ranunculaceae).

Plant Systematics and Evolution, 126, 239-42.HOWARD, R. A., 1970. Lantana camara-A prize and peril. American Horticultural Magazine, 49(1),

31-6.JAIN, M. C., 1973. A study of anthocyanins and proanthocyanidins from some Indian plants. Ph.D.

Thesis, University of Delhi, Delhi, India.KAY, Q. O. N., 1976. Preferential pollination of yellow-flowered morphs of Raphanus raphanistrum by

Pieris and Eristalis spp. Nature, 261, 230-2.KEVAN, P. G., 1978. Floral colouration, its calorimetric analysis and significance in anthecology. In

The pollination offlowers by insects. Ed. A. J. Richards. Academic Press, New York and London.Pp.51-79.

LLOYD, D. G., 1969. Petal polymorphism in Leavenworthia (Cruciferae). Contributions of GrayHerbarium, Harvard University, 198, 6-40.

MAGFORD, D. J., 1974a. Flower colour polymorphism in Cirsium palustre. Heredity, 33,241-56.--1974b. Flower colour polymorphism in Cirsium palustre. 2. Pollination. Ibid. 33, 257-63.MATHUR, GITA, 1976. Physico-chemical studies on the phenolic constituents of seeds of Antigonon

leptopus. M.Sc. Thesis. University of Delhi, Delhi, India.--1983. Flower colour changes and pollination in Lantana camara. Ph.D. Thesis, University of

Delhi, Delhi, India.--and MOHAN RAM, H. Y., 1978. Significance of petal colour in thrips-pollinated Lantana camara.

Annals of Botany, 42, 1473-6.MCGREGOR, S. E., 1976. Insect pollination of cultivated crop plants. U.S.D.A. Agriculture Handbook

No. 496, 1-411.SHARMA, NEELAM, and SmvANNA, K. R., 1983. Lectin-like components of pollen and complementary

saccharide moiety of the pistil are involved in self-incompatibility recognition. Current Science, 52,913-15.

STIRTON, C. H., 1978. Tickberries on the march. Veld and Flora (March 1978), 8-11.WAINWRIGHT, C. M., 1978. The floral biology and pollination ecology of two desert lupines. Bulletin of

the Torrey Botanical Club, 105(1), 24-8.

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