Cucumis sativus L. (Cucumber)

Cucumis sativus (cucumber), a creeping plant of the family Cucurbitaceae widely cultivated for its fruit, probably originated in northern India. It has been cultivated in India for 3000 years and the related species, Cucumis hardwickii Royle, has been found in the Himalaya mountain area. It is a tender annual with a rough, succulent trailing stem and stalked hairy leaves with three to five pointed lobes; the stem bears branched tendrils by which the plant can be trained to supports. The short-stalked, yellow, bell-shaped flowers are unisexual, but staminate and pistillate ones are borne on the same plant; the latter are recognized by the swollen warty green ovary below the rest of the flower. Flowers are insect-pollinated. Hives of bees are commonly placed near plantings in frames or fields or inside greenhouses to ensure pollination and fruit setting. The chromosome number is 2n = 14.

The heat requirement of the cucumber is one of the highest among the common vegetables. There are three groups of varieties, based on adaptability and use: (1) very large-fruited, strong growing varieties adapted only to greenhouse or frame culture. Several English greenhouse varieties form fruits without pollination and seed formation, and are generally much larger than those popular in the USA; (2) large-fruited, outdoor-grown and Japanese greenhouse varieties for slicing and pickling, generally having white spines; (3) small-fruited prolific varieties grown outdoors principally for making pickles, having black spines.

Cucumber fruit forms a bitter substance, cucurbitacin C, when cultivated at a low temperature under conditions of water starvation or overaddition of nitrogen. Cucurbitacins are a group of tetracyclic triterpenes, commonly referred to as “bitter principles of cucurbits”, which have antineoplastic and anti-gibberellin activity. They are isolated from various species of cucurbitaceous plants, known since antiquity for their beneficial and toxic properties. The plants have been used as vermifuges, emetics, narcotics, and antimalarials, and have been implicated in sporadic livestock poisoning in S. Africa. Seventeen cucurbitacins have been isolated, mostly from plants of the Cucurbitaceae family, but also from the Begoniaceae, Cruciferae, Datisceae, Euphorbiaceae, and Scrophulariaceae.

The food value of the cucumber is low, although the fruit contains vitamin A and C and free amino acids, but it is popular for salads and relishes. The Sikkim cucumber, C. sativus var. sikkimensis, is a large-fruited form, reaching 15 inches long and 6 inches thick, grown in Sikkim and Nepal. The West Indian gherkin, Cucumis anguria, has small, slender vines, and abundant small ellipsoid green fruit covered with warts and spines. It is used for pickling.

Cucumber (Cucumis sativus) is one of the plentiful sources of enzymes in plant. These enzymes include ascorbate oxidase, shikimate dehydrogenase, isomerases, and xylanase. However, these enzymes are not unique in cucumber seed or tissue, but widely distributed within the plant kingdom, although in cucumber enzymes there are several variations of isozymes or differences in substrate specificities compared with the enzymes from other plants. The reason for the extensive studies of enzymes from cucumber is that they can be easily obtained, as the seed and fruit is found in most countries.

In this post, we focus on the production of ascorbate oxidase in in vitro culture since the enzyme is particularly useful, the pure enzyme being distributed commercially.

In Vitro Cultivation

Plant cell cultures are a potential source of medically important substances, such as alkaloids, steroids, vitamins, pigments, and enzymes. Induction mechanisms of enzymes responsible for secondary metabolism in cultured plant cells have been studied with a view to high productivity of useful metabolities.

Conclusions

Peelings of cucumber (Cucumis sativus) were induced to form callus, which in turn produced ascorbate oxidase, on Murashige-Skoog basal medium with plant hormones. Cell lines which produced high levels of ascorbate oxidase and had a high growth rate were selected. Addition of 100 times more copper, a prosthetic metal of ascorbate oxidase, than that in the basal medium resulted in a significant increase in enzyme activity. A suspension culture of the cells was also established, which was found to produce ascorbate oxidase in the medium. The secretion of the enzyme from the cells was stimulated by addition of calcium ions. Maximum cell yield and maximum levels of ascorbate oxidase were obtained at about the 20th day by shake culture, but similar growth and enzyme activity were found at the 10th day in an air-lift type jar fermentor.