1458 GENETICS: ALSTON ET AL. PROC. N. A. S. 3 Gilbert, W., J. Mol. Biol., 6, 374, 389 (1963). 4Takanami, M., these PROCEEDINGS, 52, 1271 (1964). 5Nirenberg, M., P. Leder, M. Bernfield, R. Brimacombe, J. Trupin, F. Rottman, and C. O'Neal, these PROCEEDINGS, 53, 1161 (1965). 6 Schuster, H., J. Mol. Biol., 3, 447 (1961). 7 Michelson, A. M., and M. Grunberg-Manago, Biophim. Biophys. Acta, 91, 92 (1964). 8 Nirenberg, M., and J. H. Matthaei, these PROCEEDINGS, 47, 1588 (1961). 9 Brenner, S., A. 0. W. Stretton, and S. Kaplan, Nature, 206, 994 (1965); Stretton, A. 0. W., and S. Brenner, J. Mol. Biol., 12, 456 (1965). 10 Weigert, M. G., and A. Garen, J. Mol. Biol., 12, 448 (1965). 11 Notani, G. W., D. L. Engelhardt, W. Konigsberg, and N. D. Zinder, J. Mol. Biol., 12, 439 (1965). 12 Capecchi, M. R., and G. N. Gussin, Science, 149, 417 (1965). 1 Crick, F. H. C., The Wobble Theory (manuscript circulated to Information Exchange Group No. 7, National Institutes of Health, June 1965). 14Nirenberg, M. W., and co-workers, in preparation. 15 Holley, R. W., J. Apgar, G. A. Everett, J. T. Madison, M. Marquisee, S. H. Merrill, J. R. Penswick, and A. Zamir, Science, 147, 1462 (1965). 16 Jukes, T. H., Am. Scientist, in press. HYBRID COMPOUNDS IN NATURAL INTERSPECIFIC HYBRIDS* BY R. E. ALSTON, H. ROSLER,t K. NAIFEH, AND T. J. MABRY CELL RESEARCH INSTITUTE AND DEPARTMENT OF BOTANY, UNIVERSITY OF TEXAS Communicated by Wilson S. Stone, September 9,1965 Since the more recent applications of chemical methods to the study of natural interspecific hybridization, there has been considerable interest in the theoretical question of whether or not new structural configurations occur in such hybrids; i.e., hybrid-specific products formed by the combined enzymatic complements of the parents. Many years ago, Reichert' called attention to the fact that hybrids oc- casionally exhibited unexpected flower colors. The appearance of new compounds has been suggested from chemical analyses of interspecific hybrids. Alston and Turner2 described four hybrid-specific flavonoids in the leaves of the hybrid Baptisia leucantha X B. sphaerocarpa, but the compounds were later shown to occur in the flower petals of the latter species.3 Other sporadic suggestions of the occurrence of such hybrid-specific substances have not been followed by definitive experimental proof of their existence. Diverse genetic studies of flavonoid compounds (the only such extensively investigated plant secondary compounds) have invariably shown that simple mendelian mechanisms govern qualitative differences in these com- pounds.4 From current knowledge of the types of flavonoid compounds which are widely distributed in plants, it is possible to predict a large number of ways in which hybrid substances might occur. This question is important to systematic studies utilizing variability in the patterns of secondary compounds as systematic criteria. We are concerned here with a number of hypothetical compounds which could be expected to exist in the following natural hybrids of Baptisia: B. leucantha X B. sphaerocarpa; B. alba X B. tinctoria; and B. alba X B. perfoliata. Other hybrid- type molecules may be predicted to occur in other known Baptisia hybrid combina- Downloaded by guest on September 26, 2021 VOL. 54, 1965 GENETICS: ALSTON ET AL. 1459 tions, but in these other situations the necessary 2 3. R chemical investigations have not yet been completed. HO 0 2OH Since we are concerned at this time only with flavonol I L /OH glycosides of the kaempferol and quercetin series, the 6 OH'N numbering system assigned to the flavonol nucleus OH 0 should provide sufficient information to follow the FIG. 1.-Flavonol ring struc- discussion (Fig. 1). ture and numbering system. = IdentificationIdentzflcaticmof Flavonoids.-Chromatographic~ ~ ~ CRKaempferol,= OH. R H; quercetin, methods for the crude plant extracts and for the detection of the flavonoids were similar to those reported in our previous work.' Complete characterization of the glycosidic moieties of compounds 74, 75, and 77 has not been achieved, but it is known that 74 is a 3-monoglycoside of quercetin, and 75 and 77 are 3-mono- and diglycosides of kaempferol, respectively. The complete chemical characterization of these compounds is not central to the present discussion. Compound 76 is rutin; (quercetin 3-[6-0-(a-L-rhamno)-13-D-glucoside] i.e., quercetin 3-f3-rutinoside). It has been isolated from Baptisia alba and identified, utilizing such chemical criteria as NMR spectroscopy and by comparison with authentic material. The details of the structure elucidation of compounds 68-71 of Baptisia sphaero- carpa will be reported elsewhere;6 therefore, the different techniques required will only be summarized here. Compounds 70 and 71 were obtained crystalline and their structures were determined primarily by NMR spectroscopy of the tri- methylsilyl ethers.7" Independent confirmation of the glucosyl moieties was effected by enzyme hydrolysis with emulsin.8 In addition, acid hydrolysis of all the glyco- sidic linkages followed by gas chromatographic analysis of the trimethylsilylated sugars7b determined the nature of-the individual sugars present. Compound 71 is quercetin 3-f-D-glucosyl-7-,B-rutinoside, and compound 70 is quercetin 3,7-di-,B-D- glucoside. Compound 71 was converted to a 5,3',4'-trimethyl-ether whose NMR spectrum was identical in all respects with the spectrum of the compound obtained by oxidation of hesperidin (5,3'-dihydroxy4'-methoxy-flavanone-7-,B-rutinoside) to the corresponding flavonol, glucosylation at the 3-position, and finally methylation of the phenolic hydroxyl groups. This confirms the identification of compound 71 as quercetin 3-,B-D-glucosyl-7-,B-rutinoside. Compound 69, a product of partial hydrolysis of 71 with 10 per cent acetic acid, is quercetin 7-0-rutinoside; 3-glycosyl groups are units known to be rapidly hydrolyzed by acid treatment relative to the 7-glycosyl group. Compound 68, a product obtained by partial acid hydrolysis of quercetin 3,7-di-,B-D-glucoside (70), is quercetin 7-,B-D-glucoside. A compound designated as 71a occurs in Baptisia alba and chromatographs the same as compound 71. However, it yields rutin (76), upon hydrolysis by emulsin. Thus, compound 71a is quercetin 3-f3-rutinoside-7-f3-D-glucoside and differs from compound 71 only in the position of attachment of the sugar moieties to the querce- tin nucleus. Quercetin 3-f3-rutinoside-7-f3-D-glucoside was subsequently synthe- sized from rutin, and the synthetic material ran at the same chromatographic posi- tion as compound 71a isolated from B. alba, thus providing additional proof of the identification of compound 71a. Kaempferol 7-f3-neohesperidoside was obtained from the flavanone glycoside naringin by standard methods. Partial hydrolysis of the neohesperidoside afforded Downloaded by guest on September 26, 2021 \.;;. ...A ha. .4,> Up.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I......... ..:....~~ ~ ~ ~ ~ ~ ~ ~ ~ .:..... ....'....... ~3/-~~~~~ (a) 77 .-C:~7~ ~ b t-butanol-aceticacid-water351 L 16~~~~~6 t*butoacet acdwater(3:1: Downloaded by guest on September 26, 2021 VOL. 54, 1965 GENETICS: ALSTON ET AL. 1461 kaempferol 7-f3-glucoside. Kaempferol glycosides of the duckweed, Wolffia punc- tata,9 were utilized to establish the probable locations of kaempferol analogues of compounds 70 and 71a. Figure 2 illustrates the positions of the various compounds which have been dis- cussed above as they occur in the two-dimensional solvent system used for screen- ing purposes. The actual chromatogram is derived from a natural hybrid. Results.-Table 1 indicates the known flavonol compounds found in the four species now being considered. The yellow-flowered species (B. perfoliata, B. TABLE 1 FLAVONOLS OF Baptisia SPECIES B. Ieu. B. alba B. sphaerocarpa B. tinctoria B. perfoliata L F L F L F L F L F Quercetin 3-glycoside74 + tr + tr 0 + 0 0 0 0 Quercetin 3- rutinoside 76 + tr +++ + 0 tr 0 0 0 0 Kaempferol 3-glycoside 75 + tr 0 0 0 0 0 0 0 0 Kaempferol 3-digly- coside 77 + tr + tr 0 0 0 0 0 0 Quercetin 7-p-D- glucoside 68 0 0 0 0 0 + 0 + 0 0 Quercetin 7-,p-rutino- side 69 0 0 0 0 0 + 0 + 0 0 Quercetin 3,7-di-p-D- glucoside 70 0 0 tr tr 0 + 0 + 0 0 Quercetin 3.j-D-glu- cosyl-7-19- rutinoside 71 0 0 0 0 0 + 0 + 0 0 Quercetin 3-g-rutino- syl-7-,B-D- glucoside 71a* 0 0 + + 00 0 0 0 0 * Originally considered to be a single compound. + + +, The major flavonoid component; +, present in moderate concentration; tr, trace; 0, not detected. sphaerocarpa, and B. tinctoria) produce either no flavonols at all or 7- or 3,7-glyco- sides of quercetin. The white-flowered species (B. leucantha and B. alba) produce flavonol 3-mono- and 3-diglycosides of both kaempferol and quercetin. B. leucantha produces no 7-glycosides, but B. alba produces certain 3,7-glycosides of quercetin only. Figure 3a-c illustrates the compounds of the groups discussed here which are present in the combinations of parental species and their hybrids. By consulting the data of Table 1 and Figure 3 it may be seen that in certain FIG. 2.-(a) Two-dimensional chromatogram of leaf extract of natural hybrid between Baptisia leucantha and B. sphaerocarpa showing compounds of interest to the present study. (b) Compounds of the hybrid shown in (a) which are relevant to the present discussion: (68) quercetin 7-f,-D-glucoside; (69) quercetin 7-,B-rutinoside; (70) quercetin 3,7-di-#-D-gluco- side; (71) quercetin 3-0-D-glucosyl-7-j3-rutinoside; (71a) quercetin 3-0-rutinosyl-7-o-D- glucoside; (74) quercetin 3-glycoside; (75) kaempferol 3-glycoside; (76) quercetin 3-fl- rutinoside; (77) kaempferol 3-diglycoside.