NATURE 187: 240-241 (July 16, 1960)
Flavonoid Pigments of Lathyrus odoratus
J. B. Harborne

ALTHOUGH the genetics and chemistry of flower colour variation in the garden sweet pea, Lathyrus odoratus, have been much investigated1, none of the pigments present has yet been fully characterized. As part of a general study of flavonoid production in garden plants2-4, these pigments have now been analysed by means of paper chromatography and absorption spectrophotometry. Since the sweet pea varieties used by earlier investigators were not available, comparable colour forms were chosen from the wide range of present-day varieties. Examination by chromatography divided them into three main classes, depending on whether their anthocyanins were derived from the orange pelargonidin, the magenta cyanidin or the mauve delphinidin. Three deeply pigmented varieties, 'Air Warden', 'Harrow' and 'Jupiter', representing respectively each of these colour classes, were chosen for detailed examination since they contained the greatest number of pigments.

Table 1. OCCURRENCE OF FLAVONOIDS IN SWEET PEA COLOUR VARIETIES

Variety Anthocyanins Flavonol glycosides
'Air Warden'
scarlet cerise (also other varieties:
orange and salmon shades)
pelargonidin
 3-rhamnoside
 5-glucoside-3-rhamnoside*
 3-glucoside
 3-xylosylglucoside
 3:5-diglucoside
kampferol
 3-rhamnoside*
'Harrow'
deep carmine (also other varieties:
pink and rose shades)
cyanidin and peonidin
 3-rhamnoside
 5-glucoside-3-rhamnoside*
 3-glucoside
 3-xylosylglucoside
peonidin
 3:5-diglucoside
kampferol and quercetin
 3-rhamnoside*
'Jupiter'
deep purple (also other varieties:
lilac, mauve and blue shades)
delphinidin and petunidin
 3-rhamnoside
delphinidin, petunidin and malvidin
 5-glucosids-3-rhamnoside*
kampferol, quercetin and myricetin
 3-rhamnoside*
* Major glycosides; minor flavonol glycosides not shown.

Nineteen anthocyanins and three flavonol glycosides were isolated and identified by means of methods already described2. Their distribution is indicated in Table 1. Paler-coloured varieties generally contained the same pigments as the intensely coloured types though in less amount, except that the anthocyanidin 3-rhamnosides were completely lacking. Five white varieties which were examined contained the same flavonol glycosides as either 'Air Warden' or 'Harrow'; a myricetin-containing white form equivalent to 'Jupiter' was not found. Besides the three flavonol 3-rhamnosides shown in Table 1, several other flavonol glycosides were present in small amounts in most varieties. Three (that occurred with kampferol 3-rhamnoside in the white variety 'Valerie') were kampferol derivatives which had two or more sugar residues, of which one, at least, in each case was rhamnose. 'Valerie' also contained the cinnamic acid related to kampferol, namely, p-coumaric acid. It was present esterified both with glucose and with a rhamnosylglucose (probably rutinose). The glucose ester is the same compound that has recently been identified in potato berries5 and flowers of Primula obconica (Corner, J. J., and Harborne, J. B., unpublished work); the other ester has not yet been described.

The presence in Lathyrus of two new series of anthocyanidin glycosides (that is, the 3-rhamnosides and 5-glucoside-3-rhamnosides) is noteworthy since the 3-substituted sugar, in almost all the known anthocyanins, is glucose. The new pigments have much higher RF values than the corresponding glucosides in all the usual solvent systems. Furthermore, they are much more resistant than 3-glucosides and 3:5-diglucosides to hydrolysis by fungal anthocyanase (see ref. 6); the 5-glucoside-3-rhamnosides, for example, gave good yields of the corresponding 3-rhamnosides after incubation for 2 hr. with excess enzyme at 37°C. and pH 3-9.

Glycosides of all six common anthocyanidins are, with one exception, represented in both the new series: the exception is malvidin 3-rhamnoside which has, however, been provisionally identified on the basis of RF values in wild Lathyrus sativus, following the observation (Pecket, R. C., private communication) that an unusual malvidin derivative was present in that species. Pecket found that other species of Lathyrus (including a wild L. odoratus) contained only 3-glucosides. The present discovery of as many as five different kinds of glycoside in the sweet-pea shows that domestication has had a very marked effect on pigment synthesis in this species. The only other plant known to contain anthocyanin mixtures as complex as those is Streptocarpus (which is of hybrid origin4,7).

In disagreement with an earlier report1, related anthocyanidins and flavonols occur together in all the varieties examined. This agrees with findings in Solanum phureja2 and a number of other plants3,4. The genes E and Sm, which control hydroxylation of the anthocyanidins in Lathyrus, evidently also determine the flavonol hydroxylation pattern. Since flavonols and anthocyanidins are both present as 3-rhamnosides, it is likely that the same enzyme controls the addition of this sugar to both kinds of pigment. The addition of the other sugar residues must, however, be controlled by enzymes which exhibit a greater degree of substrate specificity. These results thus provide additional evidence of the close biosynthetic relationship that exists between flavonols and the anthocyanidins and of the great complexity of pigment glycosidation that occurs in highly evolved garden plants.

J. B. HABBORNE
John Innes Horticultural Institution,
Bayfordbury, Hertford, Herts.

  1. Beale, G. H., Robinson, G. M., Robinson, R., and Scott Moncrieff, R., J. Genet., 37, 375 (1939).
  2. Harborne, J. B., Biochem. J., 74, 262 (1960).
  3. Harborne, J. B., and Sherratt, H. S. A., Nature, 181, 25 (1958).
  4. Harborne, J. B., in "Plant Phenolics in Health and Disease" (in the press).
  5. Corner, J. J., and Harborne, J. B., Chem. and Indust., 76 (1960).
  6. Harborne, J. B., and Sherratt. H. S. A., Biochem. J., 65,24. P (1957).
  7. Lawrence, W. J. C., and Sturgess, V. C., Heredity, 11, 303 (1957).

Sweet Pea Bibliography