The Geography of Phytochemical Races

4.1 Across the Atlantic Ocean 177
Table 4.1 Glucosinolates in seeds of Cakile maritima and C. arabica (from Rodman, 1976)
Glucosinolate C. maritima subsp. a C. a.
CMBA CMMW CMMM CMEU CARA
Isopropyl trace 3.7 23.8 0 58.5
Allyl 80.3 12.2 9.0 99.9 23.0
sec-Butyl 16.3 84.8 34.0 0 17.0
3-Butenyl trace 0 2.8 0 trace
3-Methylthiopropyl 1.0 trace 4.9 trace 0
4-Methylthiobutyl 0 0 12.1 0 0
5-Methylthiopentyl 0 0 10.8 0 0
a CMBA = subsp. baltica; CMMW = subsp. maritima from western Europe; CMMM = subsp.
maritima from the Mediterranean; CMEU = subsp. euxima; C. a. = CARA = C. arabica.
Unique among the collections reported in this study was the chemistry of subsp.
euxima whose glucosinolate profi le consisted essentially of a single compound,
allyl glucosinolate.
It is interesting, and relevant, to look at Rodman’s views on the evolution of
Cakile, as discussed in his 1976 paper. Cakile arabica Velen. is seen as the primitive
species in the genus (or most closely resembling the primitive form) based on morphological
considerations, breeding system (it is strongly self-incompatible), and
the capacity to utilize the aliphatic amino acids isoleucine, methionine, and valine
for the production of glucosinolates. It is also important to note that C. arabica is
endemic to the deserts around the Persian Gulf and that the evolution of the beach
lifestyle in other Cakile species is considered to be an adaptation to the expanding
availability of sandy beach habitats associated with the development of the
Tethys Sea (proto-Mediterranean Sea). Migration of Cakile to new areas in Western
Europe was accompanied by partial relaxation of self-incompatibility, simplifi cation
of glucosinolate profi les in terms of the number of compounds, for example,
C. maritima subspecies euxima and baltica, and in some cases, elongation of the
precursor amino acids and oxidation of methylthioalkyl glucosinolates to the corresponding
sulfi nyl [308] and sulfonyl derivatives [309].
Colonization of the New World, thought to have occurred during late Pliocene
or Pleistocene times, was accompanied by further reduction of self-incompatibility
and simplifi cation of glucosinolate profi les. A complicating factor in the overall
chemical simplifi cation trend is the capacity of the New World species to utilize
aromatic amino acids as precursors in glucosinolate biosynthesis; phenylalanine is
converted to benzyl glucosinolate [310] and to 2-phenylethyl glucosinolate [311]
after one round of elongation. Rodman (1976) pointed out that it is not possible to
distinguish between this new biosynthetic pathway having been developed de novo
in New World taxa, or whether this represents a release of a repressed pathway.
It had been suggested by Rodman (1974) that the naturalized C. maritima along
the western coast of North America originated from plants growing along the shore
of the western Mediterranean. This possibility gained a good deal of support from the
discovery that the glucosinolate profi le of the North American plants bears close similarity
to that of plants from the western Mediterranean. It also appears that the western