REVIEW OF GUNNERACEAE

PHYTOCHEMICAL STUDY OF GUNNERA PERPENSA L

3.1 REVIEW OF GUNNERACEAE

Gunner a L. is a genus of herbaceous flowering plants and is the only member of the family Gunneraceae. Gunnera was previously placed within the family Haloragaceae due to its vegetative habit and the endosperm-rich seeds, but later studies on the morphology, anatomy, embryology and palynology accentuate the differences between Gunnera and the Haloragaceae taxa.1' '

The genus was named in honour of the Norwegian bishop and botanist Johan Ernst Gunnerus (1718-1773). The plant has existed for at least 95 million years and there are approximately 50 species mostly distributed in the southern hemisphere (Fig. 3.1). Their natural populations are restricted to super humid areas with heavy rainfalls, on riverbanks, near waterfalls and close to wells.4,5' The characteristic features of the species are long, slender and fleshy stems, rhubarb-like leaves and spikes with greenish flowers. Another characteristic feature of Gunnera shared by only few angiosperms is that it contains a number of separate vascular strands in the stems and petioles, which is indicative that Gunnera evolved from aquatic ancestors.

The genus is interesting on an ecological and physiological basis for its remarkable symbiosis with cyanobacteria of the genus Nostoc} Cyanobacteria are a large, diverse and ancient group of prokaryotic autotrophs with an oxygenic photosynthesis and also perform biological nitrogen fixation, thereby using atmospheric N2 as their sole nitrogen source.

The cyanobacterium infects specialized gland organs located on the stems of the host and once it has passed into the interior of the gland the cyanobacterium also enters the Gunnera cells where it starts to differentiate the highest frequency of nitrogen-fixing cells recorded for a cyanobacterium population. A good knowledge of this symbiotic relationship may be helpful in the development of nitrogen-fixing plants.

Taxonomical studies of Gunnera have been performed with the most complete morphological revision by Schindler in 1905.

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He divided Gunnera into five subgenera based on modes of propagation and geographic distribution, i.e. Perpensum, Pseudogunnera, Milligania, Misandra and Panke.

FIGURE 3.1: Distribution of Gunnera 9

The subgenus Perpensum consists of the single African species, G. perpensa L. This was

the first species of the genus to be described and occurs in the mountains of southern

Africa and along the Great Rift to Ethiopia and also in Madagascar. It is a medium-sized

plant characterized by stout creeping rhizomes and reniform leaves. The inflorescences are

large with hermaphroditic flowers (Fig 3.2).

The subgenus Pseudogunnera includes a single species, G. macrophylla Blume occurring on the mountains of New Guinea, Solomons Islands and Sulawesi, Wallace's Line of Java, Sumatra, Borneo and in south-eastern Asia. It is a medium-sized plant with reniform leaves. It forms slender axillary stolons carrying paired opposite bracts. It is monoecious and the inflorescences are bisexual, with male flowers on the upper branches and female flowers on the lower branches.

The subgenus Milligania includes five to seven species from New Zealand as well as the single Australian species, G. cordifolia Hook. f. from Tasmania (Fig 3.3). These are all small, mat-forming stoloniferous plants lacking scales on the stem. They are monoecious, with mostly unisexual, occasionally bisexual inflorescences.

www.utas.edu.au/dicotkey/DicotKev/OTHERS/zGunntfra.htm

FIGURE 3.3: Gunnera cordifolia

The subgenus Misandra includes two small, stoloniferous species G. magellanica Lam.

(Fig 3.4) from South America, characterized by a conical ochrea covering the apical bud.

The plants are dioecious.

TABLE 3.1: Compounds isolated from selected Gunnera species.

Numb. compound G. peltata G. masafuerae G. tintoria G. magellanica

3.1 oleanolic acid + + + +

3.2 ursolic acid - - + +

3.3 lupeol + + + +

3.4 erythrodiol + + + +

3.5 urs-12-ene- 2Pt,3a-diol

+ + + +

3.6 vomifoliol + + + +

3.7 liliolide + + - +

3.8 p-sitosterol + + + +

3.9 daucosterin + + + +

3.10 uvaol - +

3.11 ionone derivatives + + +

3.12 pinoresinol + + + +

It has been reported that an extract from the New Zealand species G. hamiltonii possesses strong lipoxygenase activity and that antithrombin activity was observed from an extract of G. tinetoria from the Azores. '

OH

3.11

3.8R = H

3.9R=p-D-glucoside

HO

HO,,

3.10

OMe

3.2 BACKGROUND ON GUNNERA PERPENSA

The only South African Gunnera species is Gunnera perpensa, L. known as uGobho in 'isiZulu' and river pumpkin in English. It is widespread in Africa from Sudan, Ethiopia, Zaire, Rwanda, Uganda, Kenya, Tanzania, Zimbabwe, Mozambique and along the central and eastern areas of Southern Africa.

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It grows around the edges of the rivers and streams and is intolerant to frost. It grows in all types of soils.

\rr~•JfJ 7

X

1.

i l -

fe.

V

-'"V /

i . _ J-~""

E.J. Mendes, Haloragaceae, Ftora Zambeziaca 1978, 4, 74.

FIGURE 3.6: Geographical distribution of G. perpensa in South Africa

It is a rhizomatous, thinly perennial herb to 1 m in height with palmate leaves, tufted, near

the apex of rhizome. The green flower spikes (2-10 cm long) appear in August and the

G. perpensa is sometimes used as an ingredient in the medicine called isihlambezo (to ensure the health of a mother and a child during pregnancy) and in medicine called Inembe (taken regularly during pregnancy to ensure easy childbirth).20

Water, hexane and 100% ethanol extracts of dried root were assessed for in vitro antibacterial activity against Staphyloccocus aureus, Klebsiella pneumoniae, Bacillus subtilis and Escherichia coli and were found to be inactive in the concentrations used.21

The aqueous extract have also been tested and showed the best antibacterial activity, which is the added advantage of its use for the treatment of wound infections.

Motivated by the distinct red color of the stems and skin irritation on contact with the leaves of the plant, Drewes et al. looked at the chemical constituents of stems and leaves.

They isolated the benzoquinones (3.13 and 3.14), a benzopyran (3.15) and a phytol (3.16).

Compound 3.16 is reported as a mild irritant isolated from other plants, hence the skin irritation on handling of the plant by the authors.23 In comparing the antibacterial activity of the crude extracts of stems and leaves, the leaves showed higher activity than the stems.

Amongst the compounds isolated, the benzoquinones showed good antibacterial activity.

The leaves of the plant are used by the rural people of Eastern Cape in wound dressing.24

3.16