Morus (PROSEA Medicinal plants)

Plant Resources of South-East Asia
Introduction

List of species

Morus L.

Protologue: Sp. pl. 2: 986 (1753); Gen. pl. ed. 5: 424 (1754).

Family: Moraceae

Chromosome number: x= 14; M. alba: n= 14, M. australis: n= 14, M. nigra: 2n= 89-106, 154, 308

Major species

Morus alba L.,
M. nigra L.

Vernacular names

Mulberry (En)
Mûrier (Fr)
Moral, morera (Sp)
Indonesia: murbei (general)
Malaysia: bebesaran (general)
Philippines: amoras (Filipino)
Cambodia: moon
Laos: mon
Thailand: mon
Vietnam: dâu tằm, dâu tàu, tằm tang.

Origin and geographic distribution

Morus comprises 10-15 species and is distributed in all tropical and temperate regions; in the tropics, mainly in montane habitats. Only one species (M. macroura Miq.) is native to the Malesian region; several others have been introduced and have occasionally naturalized.

Uses

In most parts of South-East Asia it seems to be more important to cultivate mulberry trees (most often M. alba) for their leaves, which are used to rear silkworms (Bombyx mori), than for their medicinal application. Trials have been done on the species discussed below and (in Sumatra and Java) on M. cathayana Hemsl. and M. latifolia Poir. to ascertain their suitability for raising silkworms. Furthermore, the tasty fruits are highly valued and made into juice, wine, jam, etc. In India the fruits are also used as a dye.

In general, the root bark, twigs and fruits are used as restorative, tonic, pectoral, diuretic, and are prescribed to treat cough, asthma, phthisis, and other chest complaints, dropsy and rheumatism. The leaves are depurative, cooling and resolvent.

The syrup made of fresh Morus fruits is used as a refrigerant in fevers and as an expectorant in coughs and sore throats. A drink made of it has similar applications. A decoction of the leaves of Morus is used for its blood-purifying properties as a febrifuge, diuretic and galactagogue. The leaves, bruised or withered over a fire and covered in coconut oil, are used to cover wounds and against insect bites, apparently for their anti-inflammatory properties. The root-bark is used in various applications for its general restorative properties, as a remedy against toothache and as emmenagogue, and furthermore in Vietnam for similar applications as the leaves, as diuretic, antitussive and expectorant and prescribed in oedema, high blood pressure, cough, bronchitis and asthma. The bark of Morus is used as a purgative and vermifuge. Root-bark, leaves and fruits of various Morus species are considered a remedy for diabetes. The root-bark of M. alba and possibly other Morus species is also known as the oriental drug "sohakuhi", which has long been used for anti-inflammatory, diuretic, antitussive and antipyretic purposes in oriental medicine.

M. alba yields an attractive wood, and is also used in agroforestry. It is occasionally planted as a roadside tree. Its fibrous bark has been used to make paper. M. macroura wood yields a medium-quality firewood.

Properties

Preliminary pharmacological investigations of n-butanol and water-soluble fractions of M. alba root showed cathartic, analgesic, diuretic, antitussive, antioedemic, sedative, anticonvulsant and hypotensive actions in mice, rats, guinea-pigs and dogs. These experimental results seem to show some correlation with the traditional clinical applications in Chinese medicine.

The anti-inflammatory activity of the methanol extract of M. alba root has been studied in rats using the following methods: rat paw oedema, inflammatory exudation, carrageenin-induced pleurisy, cotton pellet granuloma and chronic experimental arthritis. The extract has been found to be effective in carrageenin-induced oedema and this was not due to a counter-irritant effect. It was also effective against mediator-induced (histamine, serotonin, bradykinin) oedema; it reduced the intensity of peritoneal inflammation and also inhibited the migration of leukocytes, suggesting an anti-exudative effect. The extract reduced the formation of granulation tissue and inhibited experimental arthritis, suggesting its effect on proliferative phases of inflammation and in arthritic conditions. Antipyretic studies revealed its potential to reduce body temperature in pyretic rats. The extract further possessed analgesic activity.

A series of flavone derivatives have been isolated from the root-bark of M. alba: mulberrin, mulberrochromene, cyclomulberrin, cyclomulberrochromene, mulbeeranol, and phenolic compounds albactalol, albanol A and albanol B. The flavone morin (2',3,4',5,7-pentahydroxyflavone, an isomer of quercetin) has been identified in the heartwood. Morin shows anti-angiotensin properties, with activity on blood pressure and isolated tissues of the rat. The latter effect of morin seems to be a direct action on the muscle-relaxing system. Morusinol, an isoprene-substituted flavone is found in the root-bark of M. alba together with a number of related compounds. In general these flavones are known to have some anti-tumour activity.

Eighteen N-containing sugars have been isolated from the roots of M. alba, including seven that were isolated from the leaves of M. bombycis Koidz. These N-containing sugars are: 1-deoxynojirimycin, N-methyl-1-deoxynojirimycin, fagomine, 3-epi-fagomine, 1,4-dideoxy-1,4-imino-D-arabinitol, 1,4-dideoxy-1,4-imino-D-ribitol, calystegin B₂ (= 1α,2β,3α,4β-tetrahydroxy-nor-tropane), calystegin C₁ (=1α,2β,3α,4β,6α-pentahydroxy-nor-tropane), 1,4-dideoxy-1,4-imino-(2-O-β-D-glucopyranosyl)-D-arabinitol, and nine glycosides of 1-deoxynojirimycin. These glycosides consist of 2-O- and 6-O-α-D-galactopyranosyl-1-deoxynojirimycins, 2-O-, 3-O- and 4-O-α-D-glucopyranosyl-1-deoxynojirimycins and 2-O-, 3-O-, 4-O- and 6-O-β-D-glucopyranosyl-1-deoxynojirimycins. Due to the presence of nitrogen in the molecules, some authors also refer to these compounds as alkaloids instead of N-containing sugars; this makes 3-epi-fagomine a new member of the polyhydroxylated piperidine alkaloids. Furthermore, the isolation of 1,4-dideoxy-1,4-imino-D-ribitol is the first report of its natural occurrence.

It has recently been found that the polyhydroxy-nor-tropane alkaloids possess potent glycosidase-inhibiting activities. Inhibition of glycosidases might be part of the mechanism involved in anti-hyperglycaemic effects. Calystegin A₃ (from Calystegia sepium (L.) R. Br., Convolvulaceae) is an example of a trihydroxy-nor-tropane, and the calystegins B₁(from C. sepium) and B₂ (from C. sepium and M. alba) are examples of tetrahydroxy-nor-tropanes. Calystegin C₁ (M. alba) is a new member of the calystegins, the first naturally occurring pentahydroxy-nor-tropane. The inhibitory activities of 3-epi-fagomine, calystegin B₂, calystegin C₁, and four glycosides of 1-deoxynojirimycin have been investigated against rat digestive glycosidases and various commercially available glycosidases. Calystegin C₁ was found to be a particularly potent inhibitor of rat digestive glycosidase. The β-D-glucoside of 1,4-dideoxy-1,4-imino-D-arabinatol, which is known to be a potent inhibitor of yeast α-glucosidase and mouse intestinal isomaltase, completely lost inhibitory activity against rat glycosidases. When compared with the commercially available glycosidases, calystegin B₂ performed better than calystegin C₁.

Diabetic patients experience xerostomia, a feeling of thirst and the need to frequently drink water. This syndrome is believed to be partially related to a reduced flow rate of saliva and an accompanying decrease in salivary protein components. Furthermore, many of these salivary protein constituents possess local antimicrobial properties and promote local wound healing and epidermal tissue generation. Hot water extracts and six N-containing sugars derived from M. alba leaves, have been investigated on pilocarpine-induced saliva secretion in streptozocin-induced diabetic mice. Hot water extracts (100 and 200 mg/kg, intraperitoneal) significantly potentiated the pilocarpine-induced salivary flow, but not the protein content. The N-containing sugars (37.5-300 μmol/kg) potentiated the saliva secretion, and the order of potency was 1,4-dideoxy-1,4-imino-D-arabinitol > fagomine > 2-O-α-D-galactopyranosyl-1-deoxynojirimycin. Only fagomine significantly increased the protein content in the saliva.

An aqueous methanol extract of the root of M. alba showed a hypoglycaemic effect on intraperitoneal administration in normal mice. The active component was found to be a glycoprotein called moran A. A dose-dependent activity for the purified compound was furthermore established on intraperitoneal injection in both normal and alloxan-induced diabetic mice, 7 and 24 hours after administration. The hypoglycaemic activity is also found in an ethanol extract of the leaves of M. alba. The aqueous extract of the leaves of M. alba also exhibited uterine stimulant and estrogenic activity. Clinical study of aqueous extracts of the fruits showed laxative, central nervous sytem depressant and cholecystokinin receptor binding activities. Hypoglycaemic activity in humans is not only for M. alba but also for orally administered M. nigra leaf extracts.

Morusin and kuwanon C, isolated from root bark of M. australis showed significant effects in platelet aggregation assays. An aqueous extract of M. australis showed significant antibacterial activity against Streptococcus mutans with a minimal inhibitory activity of less than 7.8 mg/ml. Small pieces of M. alba leaves inoculated with Fusarium solani f. sp. mori produced new antifungal substances. These substances can be extracted by methanol, ethanol or acetone but not with chloroform or water. An acetone extract of the non-infected leaves showed antibacterial activity against Staphylococcus species.

Description

Dioecious or monoecious shrubs or trees up to 35 m tall; bark surface fissured, exuding white or yellowish-white latex.
Leaves alternate, simple or 3-5-lobed, dentate, palmately 3-5-veined; stipules lateral, caducous.
Inflorescence axillary, spicate.
Flowers unisexual, small, with 4, free or basally united, imbricate tepals; male flowers in long catkin-like inflorescences, with 4 exserted stamens and top-shaped pistillode; female flowers in short to capitate inflorescences, tepals accrescent and succulent in fruit, ovary included, 1(-2)-locular with a single ovule, style 2-partite, staminodes absent.
Fruit a juicy syncarp, composed of many achenes enclosed in the succulent tepals; endocarp woody.
Seed subglobose, with endosperm.
Seedling with epigeal germination; cotyledons emergent; hypocotyl elongated; first leaves often palmately or pinnately lobed.

Growth and development

Growth of M. alba is initially rapid but slows down abruptly after about 10 years. Pollination is probably by wind. Morus fruits may be set without pollination and are eaten by birds, the seeds defecated and thus dispersed; dispersal by water is also known. Vesicular-arbuscular mycorrhizae are present in M. alba, M. australis and M. nigra but the degree of colonization varies.

Other botanical information

It are the light-coloured buds of M. alba that account for its name rather than the colour of its fruit, which can be almost any colour including white, lavender, red and black. The leaves may be entire to variously lobed on the same plant.

The number of Morus species is often greatly over-estimated because many cultivated forms that have arisen through hybridization have been described as species. M. bombycis Koidz. is sometimes thought to be conspecific with M. australis.

Ecology

Most mulberry species occur in warm temperate to subtropical regions, and in tropical highland areas. In temperate regions white mulberry is the most frost-hardy Morus, though some clones are damaged at 6°C whereas others can stand temperatures of -40°C. In India, white mulberry has invaded irrigated plains very rapidly. Although black mulberry seems to be much less cold-tolerant, this may vary among clones, with absolute minimum temperatures between -18°C and -12°C. In general, Morus prefers well-drained, loamy soils, but white mulberry, for example, is quite tolerant of drought and poor soils.

Propagation and planting

Morus can be propagated by seed and by cuttings, grafting and air-layering. Hardwood, softwood and root cuttings can all be used for vegetative propagation. Seeds are extremely small and the 1000-seed weight is 2.2-2.3 g. In India, M. alba is raised from seed which germinates in 9-14 days. Seedlings are pricked out when 10-15 cm tall. All but a few terminal leaves are stripped ("striplings") before seedlings are planted during the cold season or at the beginning of the rains. Cuttings with 3-4 buds are used for the production of leaves to feed silkworms. They are buried for 15-20 cm of their length, including 2 buds. The rooted cuttings are planted out in the field after two months. Spacing depends on the method of harvesting leaves and is variable, being (0.5-)0.8(-1.2) m × (1.5-)1.8-2.0(-2.5) m. When planted in paired rows, the distance between pairs is about 1.8 m, about 0.6 m within one pair, with 0.5 m in the row. Grafted M. alba gives higher leaf yields than plants raised from seedlings or cuttings, resulting in silkworm cocoons of superior quality. Experimental micropropagation was quite successful in India where shoot tip and nodal explants from a 12-year-old black mulberry tree were multiplied. Nodal explants from seedlings of white mulberry raised in vitro all rooted and were successfully transferred to a 1:1 sand-vermiculite mixture.

In vitro production of active compounds

M. alba callus cultures from the leaves give rise to cell lines, which are reported to produce a variety of compounds e.g. prenylated chalcones and phytosteroids. The yield of these Diels-Alder adducts is higher than in the intact plant.

Husbandry

Morus trees are pruned to maintain an adequate framework for effective branching. M. alba is grown as a tree, a bush or as an espalier aiming at optimum leaf production. Low cutting ("bush type") is generally practised, but semi-low and medium cutting (at 1 m height) are also known. When grown as a bush, white mulberry in India is productive for about 15 years after which period the crop is replaced. Black mulberry is pruned to a height of 1 m during the resting period; this promotes vigorous growth and the production of large-sized fruits.

Diseases and pests

The major diseases of Morus as observed in India are: powdery mildew (Phyllactinia corylea, also found in Indonesia), leaf spot (Cercospora moricola, Pseudocercospora mori) and leaf rust (Cerotelium fici). The stem borer Batocera rufomaculata is an important pest. In Thailand, the nematode Hoplolaimus seinhorsti is often found in M. alba plantations and probably associated with a root-rot disease which is widespread in the north-eastern part of the country.

Harvesting

Mature leaves of M. alba are harvested either by plucking and leaving a few terminal leaves, or by pruning, coppicing or pollarding. For harvesting there seems to be no standard procedure with regard to frequency and cutting height. In a pruning experiment with M. nigra in Indonesia neither total leaf production nor the chemical composition of the leaves was affected by the height of pruning (20, 70 and 120 cm) and the frequency (3-4 months). The roots are simply dug up.

Yield

An annual yield of 25 t fresh leaves per ha is considered acceptable for M. alba.

Handling after harvest

Harvested roots of Morus are washed and the rough part is scraped off. Then a longitudinal incision is made, the bark pounded lightly and separated from the wood, tied in bundles and dried in the sun. Harvested leaves for feeding silkworms are stored in loose heaps in cool rooms and heating, fermentation and drying-out are prevented.

Genetic resources and breeding

There are over 1000 races of M. alba, mainly to produce fodder for silkworms. In India, the techniques to induce tetraploidy in M. alba have recently been standardized and diploids, autotriploids and tetraploids are being studied, to assess their relative advantages.

Prospects

The hypoglycaemic properties of Morus deserve further attention for their possible application in diabetes. Furthermore, the anti-inflammatory properties and the wide range of traditional clinical applications warrant continuing interest in Morus.

Literature

Asano, N., Oseki, K., Tomioka, E. & Matsui, K., 1994. N-containing sugars from Morus alba and their glycosidase inhibitory activities. Carbohydrate Research 259(2): 243-255.
Boer, E. & Sosef, M.S.M., 1998. Morus L. In: Sosef, M.S.M., Hong, L.T. & Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3). Timber trees: Lesser-known timbers. Backhuys Publishers, Leiden, the Netherlands. pp. 387-389.
Chatterjee, G.K., Burman, T.K., Nagchaudhuri, A.K. & Pal, S.P., 1983. Antiinflammatory and antipyretic activities of Morus indica. Planta Medica 48(2): 116-119.
Chen, F., Nakashima, N., Kimura, I., Kimura, M., Asano, N. & Koya, S., 1995. Potentiating effects on pilocarpine-induced saliva secretion, by extracts and N-containing sugars derived from mulberry leaves, in streptozocin-diabetic mice. Biological and Pharmaceutical Bulletin 18(12): 1676-1680.
Council of Scientific and Industrial Research, 1962. The wealth of India: a dictionary of Indian raw materials & industrial products. Vol. 6: 429-439.
Ghafoor, A., 1985. Moraceae. In: Nasir, E. & Ali, S.I. (Editors): Flora of Pakistan. No. 171. Shamim Printing Press, Karachi, Pakistan. 54 pp.
Konno, C., Oshima, Y. & Hikino, H., 1977. Morusinol, isoprenoid flavone from Morus root barks. Planta Medica 42(2): 118-124.
Lim, S.H., Kim, Y.T., Lee, S.P., Rhee, I.J., Lim, J.S. & Lim, B.H., 1990. Sericulture training manual. FAO Agricultural Service Bulletin 80. Food and Agriculture Organization of the United Nations, Rome, Italy. 115 pp.
Samsijah & Sudrajat, 1975. Hama dan penyakit tanaman murbei [Pests and diseases of mulberry plants]. Laporan No 197. Lembaga Penelitian Hutan, Bogor, Indonesia. 67 pp.
Siddiqui, H.H., Malhotra, N.K. & Ramaswamy, A.S., 1975. Antiangiotensin activity of morin on the blood pressure and isolated tissues of the rat. Journal of Research on Indian Medicine 10(4): 120.

Selection of species

Authors

D.S. Alonzo