BiochemicaISystematic, sandEcology, Voi. 9, No. 2/3, pp. 205-206,1981. 0305-1978181 / 020"205~2 $02.00/0 Printed in Great Britain. © 1981 Pergamon Press Ltd.

Short Communication Epicuticular Alkanes from Desert Plants of Baja California

PETER PROKSCH, CHARLES STERNBURG and ELOY RODRIGUEZ Phytochemical Laboratory, Department of Ecology and Evolutionary Biology, University of California,

Irvine, CA 92717, USA

Key Word Index- Asclepias subulata; Asclepidiaceae; Pedilanthus macrocarpus; Euphorbiaceae; Bursera microphylla; Burseraceae; Fouquieria columnans; Fouquieriaceae; Larrea tridentata; Zygophyllaceae; epicuticular alkanes.

Plant epicuticular waves serve as a barrier and shelter against environmental stress, some of their most important functions being reduction of transpiration, resistance against pathogens and increasing of frost hardiness [1-3]. The chemical composition of epicuticular waxes is rather unique, very stable long-chain aliphatic constituents such as alkanes or lowly oxygenated compounds predominating in most cases [4]. We are interested in the amount and composition of epicuticular waxes from desert plants as affected by extreme environmental conditions. In this first paper we report the alkane chemistry of five dominant species from the Vizcaino Desert of Baja California, Asclepias subulata Denne (Asclepidiaceae), Pedilanthus macrocarpus Benth. (Euphorbiaceae), Bursera microphylla A. Gray (Burseraceae), Fouquieria columnaris Kell. (Fouquieriaceae) and Larrea tridentata (Sesse Moc. ex. DC) Coville (Zygophyllaceae) [5, 6]. Fouquieria columnaris [5], an endemic plant to Baja California and to a small part of the mainland of Mexico, is assigned by some authors to the genus Idria [7].

Asclepias subulata and P macrocarpus, both deciduous plants, showed the highest amounts of epicuticular alkanes (2.5% and 3.4% respectively per dry weight, Table 1). The large amounts of

alkanes covering their stems is a chemical mechanism for controlling the water potential. Only minute amounts of alkanes (0.1% per dry weight) were extracted from the leafy stems of L. tndentata. Chemical reduction of water loss for this plant is probably accomplished by the thick film of phenolic resins covering the surface [8]. Average yields of epicuticular alkanes compared to A. subulata and P. macrocarpus were extracted from the leaves of B. microphylla and F. columnaris (1.8% and 1.1% respectively per dry weight). The alkane profiles of the studied species were analysed by GLC (Table 1). The alkanes n-C29 and n-C31 were the dominant components in A. subulata, B. microphylla, F. columnaris, and L. tridentata; n-029 predominated in the pattern of F. columnaris (87.2%) and n-C31 in B. microphylla (54.1%). These two alkanes were nearly equally distributed in the profiles of A. subulata and L. tridentata. The alkane profile of P. macrocarpus was, in comparison, shifted to longer chain lengths with its dominating alkanes n-C31 and n-C33, which to- gether represented 85% of the total yield. The latex of P macrocarpus also contains up to 10% (per dry weight) of cis-1,4-polyisoprene (rubber) [9]. Experimental Plants were collected in January 1981 in the Vizcaino Desert of Baja California, Mexico, along the roadside between

TABLE 1. AMOUNT AND COMPOSITION OF EPICUTICULAR ALKANES FROM DESERT PLANTS OF BAJA CALIFORNIA

Total alkanes Individual alkanes (% total) Species (% dry weight) C 23 24 25 26 27 28 28 30 31 32 33 34 35 Asclepiassubulata 2.5 0.2 0.2 2.3 1.6 13.5 3.9 31.8 6.1 30.2 2.9 6.4 + 0.9 Pedilanthusmacrocarpus 3.4 + 2.4 + 9.3 1.0 47.0 2.6 37.6 + + Bursera microphylla 1.8 + + + + 4.7 + 28.9 1.9 54.1 1.9 8.5 + + Fouquieria columnan's 1.1 + + + + 7.4 + 87.2 + 5.3 + + Larrearridentata 0.1 1.0 0.6 4.5 0.6 9.0 1.8 36.7 3.6 39.7 0.9 1.5 + +

+<0.1%.

(Received28 March 1981 )

2(35

206 PETER PROKSCH, CHARLES STERNBURG AND ELOY RODRIGUEZ

Catavina and Bahia de Los Angeles. Identification was secured by comparison with voucher specimens of the UCI herbarium which were previously collected at the same sites. The plant material, stems of A. subulata and ,£ macrocarpus and foliated branches of the other species were kept fresh in ice chests until extraction. Epicuticular waxes were extracted by dipping the plants into distilled Et20 for 1 min. AIkanes were separated from the dried, evaporated extract by SiO 2 column chromatography and analysed by G LC [10]. Identifica- tion of the alkanes was by comparison with known standards.

Acknowledgements-The support of NSF-Fire Ecology grant (No. DEB79-12204), the Graduate Division of UCI and the Fu(bright Commission to one of the authors (P.P.) is gratefully acknowledged.

References 1. Kolattukudy, P. E. (ed.)(1976) Chemistry and Biochemistry

of Natural Waxes, p. 6. Elsevier, Amsterdam. 2. Tulloch, A. P. (1976) Chemistry and Biochemistry of

Natural Waxes (Kolattukudy, P. E., ed.) p. 269. Elsevier, Amsterdam.

3. Eglinton, G. and Hamilton, R. J. (1967) Science 156, 1322.

4. Kolattukudy, P. E. (ed.) (1976) Chemistry and Biochemistry of Natural Waxes, p. 2. Elsevier, Amsterdam.

5. Henrickson, J. (1972) Aliso 7, 439. 6. Wiggins, I. L. (1980) Flora of Baja California, pp. 202,

129, 589, 826. Stanford University Press, Stanford, California.

7. Wiggins, I. L. (1980) Flora of Baja California, p. 403. Stanford University Press, Stanford, California.

8. Mabry, T. J., DiFeo, D. R., Jr., Sakakibara, M., Bohnstedt, C. F., Jr. and Seigler, D. (1977) Creosote Bush, Biology and Chemistry of Larrea tridentata in New Wor/dDeserts (Mabry, T. J., Hunziker, J. H. and DiFeo, D. R., Jr., ed.) p. 116. Dowden, Hutchinson ~ Ross, Stroudsburg, Pennsylvania.

9. Sternburg, C. and Rodriguez, E. (1981) Am. J. Botany (in press).

10. Proksch, P., Behl, M. H. and Rodriguez, E. (1981) J. Agric. Food Chem. (submitted).