Alliaceae

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Alliaceae

Description

Perennial herbs with bulbs, bulb-like conns or rhizomes. Leaves simple, basally concentrated, spirally set or distichous. Inflorescence usually umbellate and with 1, 2 or more membranous spathes. Flowers generally bisexual, actinomorphic or sometimes zygomorphic. Stamens usually 6 or sometimes 5 with several staminodes, free, inserted at the base of the tepals or in the perigone-tube; Ovary superior, 3-celled, with axillary placentas, septal nectary grooves present on the ovary; Fruit a loculicidal capsule. Seeds often half-ovoid, half-globose or tetrahedral and triangular in transection, sometimes ovoid or ellipsoid to subglobose and rounded in transection.

Distribution

Chile: present South Africa: present nearly cosmopolitan: present
As circumscribed by Dahlgren et al. (1985) this segregate from Liliaceae s.l. comprises the South African Agapanthoideae, the mainly Chilean Gilliesioideae, and Allioideae with the neogeic tribe Brodiaeeae and the nearly cosmopolitan Allieae.

Phytochemo

All members of Allium emit after wounding characteristic odours known as 'onion odour' and 'garlic odour'. Everywhere mankind met species of Allium, it made use of their spicy, culinary and medicinal properties. Allium taxa, including a lot of cultivars of the onion group (A. cepa), the garlic group (A. sativum) and the leek group (A. porrum), are cultivated from time immemorial in southern Europe and the Near East. Allium kurrat seems to have been taken in cultivation in ancient Arabia, Palestina and Egypt and A. chinense, fistulosum, macrostemon and tuberosum had or still have many ancient cultivars from India to China and Japan. Chives (A. schoenoprasum) were taken in cultivation in postroman time in Europe.

There are three classes of secondary metabolites which apparendy are produced by all species of Allium. Firstiy a range of sulphur compounds which originate all after wounding from genuine S-alkyl- and S-alkenylcysteines and are responsible for the characteristic odour. Secondly complex mixtures of biologically active saponins with C27 steroidal sapogenins. Thirdly phenolic compounds which seem to be mainly derivatives of the flavonols kaempferol and quercetin and simple phenolic acids such as protocatechuic and ferulic acid, Perhaps biogenic amines and simple amides and alkaloids represent another group of characteristic Allium metabolites.

The totality of the presently known chemical compounds indicates that Allium, and possibly Allioideae, have one taxon-characteristic chemical character, namely production of S-alkylated cysteines. By their saponins Allioideae are reminiscent of that part of Lilii-florae which is classified by Dahlgren et al. (1985) in Dioscoreales and Asparagales. Biochemically Allioideae are clearly distinct from Amaryllidaceae s.str., Haemodoraceae, Hypoxidaceae and all the families reunited in Liliales sensu Dahlgren et al. (1985).

Phytochemistry and chemotaxonomy of Alliaceae were discussed twice by Hegnauer (1963, 1986) sub Liliaceae; in these treatises many references can be found. Some results of recent phytochemical investigations will shortly be mentioned in the following alineas.

Sulphur compounds are usually considered to be mainly responsible for the medicinal virtues of garlic and other species of Allium. This initiated a large number of chemical, analytical and medicinal publications; see e.g. Ziegler et al. (1989), Sticher (1991), Block (1992), Hikino et al. (1986) and others. The S-alkylated cysteines are stored in fresh bulbs, leaves and seeds of Allium species as γ-glutamyl peptides. During long storage or on wounding a lot of mostly enzymatic transformations can take place, e.g.: generation of the free S-alkylated cysteines; oxidation to S-alkylated cysteine sulfoxides (the S-allyl-derivative is alliin); transformation of the sulfoxides to dialkyl thiosulfinates (the diallyl-derivative is allicin); this last step is catalysed by the enzyme alliinase which is only known from the genera Allium and Nothoscordum. S-rra^-l-propenylcysteine (the precursor of the lachrimatory factor of onion), S-allyl-cysteine (the precursor of alliin and allicin), S-methylcysteine and S-propylcysteine occur in variable amounts and proportions in different species of Allium (Lawson et al*. 1991). New transformation products of allicin are the ajoenes and the vinyldithiins of A. sativum (Sticher 1991). Onions produce on grating and slicing variable amounts of thiopropanal-S-oxide (lachrimatory factor), 2-rnethyl-2-pentenal, propanethiol, dipropyldisulfide, propenyl-propyldisulfide and others (Tokitomo & Kobayashi 1992). The cepaenes and deoxycepaenes of A. cepa are isomers of the A. sativum ajoenes (Block & Zhao 1992). Other types of sulphur compounds were isolated from subterranean parts of Tulbaghia violacea (Burton et al. 1992).

All species of Allium produce monodesmosidic spirostanol-type and bidesmosidic furo-stanol-type steroidal saponins. A review treating 26 species, 26 sapogenins and 40 saponins was published by Kravets et al. (1990). Of the sapogenins mentioned agiogenin, alliogenin, the ansurogenins, cepagenin, gantogenin, the karatavigenins, luvigenin, neo-agigenin and its 6-benzoate and neoalligenin are new C27 Agiogenin was first isolated from A. giganteum (therefore not aiogenin: Dahlgren et al. 1985: 195). New saponins were isolated among others from bulbs of A. ampeloprasum (Morita et al. 1988), bulbs of A. chinense (Matsuura et al. 1989a), bulbs of A. giganteum (Sashida et al. 1991), flowers of A. porrum (Harmatha et al. 1987), bulbs and roots, but not leaves, of A. sativum (Matsuura et al. 1988,1989b) and bulbs of A. vineale (Chen & Snyder 1987, 1989). The vineale saponins have molluscicidal activity; the leek saponin aginoside is concentrated in flowers and makes them unpalatable and toxic for larvae of the leek moth; the spirostanolsaponins aginosideprosapogenin and ampeloside-Bs1 of A. ampeloprasum are fungitoxic whereas the bidesmosidic furostanol saponins ampeloside-Bf1 and -Bf2 did not inhibit the two species of Fungi tested; the same biological properties were observed in A. sativum with the fungitoxic eruboside-B, a spirostanolic β-chlorogenin-3-glycoside, and the inactive bidesmosidic furostanols proto-eruboside-B, sativoside-B 1 and sativo-side-R1. Bulbs of Tristagma uniflora yielded saponins with tigogenin, neotigogenin, two 25-epimeric 5α,6-dihydronuatigenins and two 25-epimeric 5α,6-dihydroisonuatigenins as aglycones (Brunengo et al. 1985). According to Koch (1992) the steroidal sapogenins may be involved in some of the therapeutical effects of onion and garlic.

Commercially available fresh leaves of A. tuberosum yielded three new kaempferol bis- and tris-glycosides with one of the sugar hydroxyls acylated by ferulic acid, a kaempferol and a quercetin 3,4'-bisglucoside and kaempferol-3-sophoroside (Yoshida et al. 1987).

Bulbs of A. chinense (= A. bakeri) yielded diallyl disulfide, the dihydrostilbene lunu-laric acid and the amides N-p-coumaroyltyrarnine and N-feruloyltyramine (Okuyama et al. 1986; Goda et al. 1987). Another amide, aurantiamide acetate, was isolated from whole plants of A. wallichii (Talapatra et al. 1989); these authors also reported isolation of the furanocoumarin imperatorin from the same plant without giving yields nor mentioning vouchers. A simple alkaloid related to N-methyltyramine and called alline (do not confound with alliin) was isolated from A. ramosum (= A. odorum) (Tashkhodzhaev et al, 1985) and sequently demonstrated to occur also in A. altaicum, anisopodium, senescens, splendens, stellerianum and victorialis, but not in A. leucocephalum and A. schoenopra-sum var. sibiricum (Antsupova & Polozhiy 1987).

Bulbs of all investigated Allium species store fructans (Hegnauer 1963; Deinko 1985) and seeds store fatty oils with much linoleic acid (Hegnauer 1963; see for unsaturated fatty acids of Allium taxa also Deinko 1985). According to Afzal et al. (1985) lipids of bulbs of A. sativum contain much polyunsaturated fatty acids, such as linoleic, arachidonic (= eicosa-all-cis-5,8,11,14-tetraenoic) and an eicosapentaenoic acid.

Phytoalexins were induced in bulb scales of A. cepa by Botrytis cinerea, and subsequently two fungistatic compounds could be isolated; they were called tsibulin-1,C11H18O2, and -2,C13H22O2, after the Ukrainian name 'tsibulya' for onion; the tsibulins are 1-alkyl-cyclopentan-2,4-diones (Tverskoy et al. 1991).

Van Damme et al. (1991) prepared lectins from bulbs of five species of Allium and compared them with lectins of bulbs of six species of Amaryllidaceae s.str.; the taxonomic meaning of these results is not yet clear. (R. Hegnauer)

Citation

Dahlgren, Clifford & Yeo, Fam. Monocot. 1985