Phytolacca americana L. (Pokeweed)

Phytolacca americana (Phytolaccaceae), in addition to serving as an occasional food, is a medicinal plant listed officially in the United States and in the French and Japanese Pharmacopeia. The plant has been used in folk medicine as a diuretic, purgative, antiscorbutic, and antisyphilitic agent (Fournier 1948). The roots are reputed in Korea to treat edema and rheumatism. At present, P. americana is used in some French homeopathic preparations to alleviate influenza, acute amygdalis, quinsy, mammary and rheumatic pains, and chronic pharyngitis. The plant and its tissue cultures have been investigated as a source of saponins, betalains, mitogens, and antiviral proteins.

Botanical Traits and Classification

The genus Phytolacca belongs to the family Phytolaccaceae, order Centro-spermae (or Caryophyllales), suborder Chenopodiineae (which includes ten families accumulating the pigments betalains). This suborder is closely related to the anthocyanin suborder Caryophyllineae. Both suborders are derived from a common ancestor, probably preadapted for C4 photosynthesis, which had evolved ring-like inclusions composed of proteinaceous filaments, contained in the sieve-element plastids in all the Centrospermae families. About 35 species are assigned to the genus.

Phytolacca americana L. (synonym: P. decandra L.; common names: English: pokeweed, pokesallet, pokeberry, pigeon berry, American scarlet berry; French: raisin d’Amerique; German: Kermesbeere) is a perennial herb, somewhat woody at the base, growing to a height of 1-3 m. Stems are subdichotomously branched, often red, with decurrent ridges from the leaf bases. Leaves are ovate-lanceolated, petiolated. Spikes of greenish white flowers turn reddish in fruits. Fruits are depressed-globose, dark purple juicy berries, about 10 mm in diameter (); they are dispersed by birds. P. americana originated in North America and was introduced into numerous countries in Europe. Thereafter, the species was spread to other continents and is now established in South Africa, Japan, Australia, New Zealand, Argentina, etc., so that it is now on a way to become an ubiquitous weed.

Optimal conditions for germination of P. americana seeds have been investigated (): alternating temperatures, light, and nitrate are three factors of importance to obtain appreciable seed germination; soaking seeds in concentrated H2S04 prior to sowing increases rates of germination. Juice of pokeweed fruits and extracts of freshly harvested mature leaves stems or immature fruits are inhibitory for seed germination; in contrast, extracts of juvenile leaves have no effect on seed germination.

P. americana has long been considered poisonous for humans and animals. The more toxic organs are roots, stems and leaves being less toxic (); however, poisoning of horses and bovids was reported after consumption of pokeweed leaves. There are conflicting opinions about the toxicity of berries, some traditional sources indicating medicinal values when fermented. The juice was formerly used as a dye to color jam and wine. Yet, as this practice seemed to be hazardous, the cultivation of the plant was forbidden in Portugal (Le Maout and Decaisne 1876). Pokeber-ries were reported to be toxic to cattle, horses, and turkey poults, despite the fact that many wild birds are known to consume these fruits. Ingestion of berries by cows produced gastrointestinal disturbances and eventually death caused by paralysis of the respiratory organs. Peripheral blood plasmocytosis was found in children exposed to pokeberries. Presence of toxins has been described by Driver and Francis. On the other hand, other reports claimed that the seeds are extremely toxic when ingested. Despite the toxicity of all parts of the plant, young stems and leaves seem to be edible if cooked: several authors claimed that P. americana sprouts were eaten locally in the United States or in France as a vegetable (Bois 1927).

Conclusions and Perspectives

The studies on Phytolacca americana tissue cultures have shown that a number of economic and medicinal compounds may be produced in vitro.

From the pharmaceutical point of view, an important finding is that RIPS can be produced in cell suspensions. As P. americana is a very common species, easy to culture, it would be uneconomical to use cells grown in vitro for producing these proteins. However, cultures in vitro might be of interest since they are available throughout the year. Another important point is the fact that PAP-C slightly differs from the other PAPS isolated in the plants. It is well known that somaclonal variations often occur in tissue culture and therefore it may be expected that other forms of PAPS, some of them having more active biological properties, exist in these tissues.

Another promising result is the accumulation of betalains in callus and suspension cultures. At present, the data available regarding the effect of environmental factors on these cultures represent only an initial step on the way to be explored. Increasing the accumulation of the pigment might be of interest with the aim of producing the dye on a commercial scale.