Milky juice

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Leaking poisonous milky sap of the spurge (Euphorbia).

Under latex or chyle is understood that some of organisms - taxa liquid formed secretion , which in the plant body in milk tubes or in the hyphae of fungi is formed and transported. The name of the milky juice comes from its milky, cloudy appearance. The milky sap is usually white, rarely yellow to orange. Milky juice has a more or less thick consistency and hardens in the air. A well-known form of the milk juice is latex, from which the rubber is extracted. Also known is the milky juice from the unripe capsule fruits of the opium poppy , from which the opium and the alkaloids it contains ( e.g. morphine ) are obtained. Plants with milky sap were often viewed as magic or witch plants in ancient times and in the Middle Ages .

Organisms in which milky sap occurs

Opium poppy, Papaver somniferum , from whose milk opium can be obtained.
Milky juice of Papaver somniferum obtained by scratching immature seed pods provides opium when dried.

Plant families in which milky sap are leading representatives include:

Milky sap is also found in some mushrooms , for example in the genus of the milklings ( Lactarius ), whose hyphae are white ( Lärchen-Reizker ) or red-orange ( Edel-Reizker , Fichten-Reizker , Salmon-Reizker , Wechselblauer Edel-Reizker , wine-red pine -Reizker , Spangrüner Kiefern-Reizker ) or blue-green (blue- milked Reizker , Indigo-Reizker ) contain milk juice with saturated fatty acids. In some species, the milky sap changes color in the air. Some dairy pigs taste more or less hotly burning raw, some types can lead to gastrointestinal irritation, even when cooked.

Chemical composition

Milky juice consists mainly of isoprenoids or terpenes , which are emulsified in various proportions in an aqueous base, depending on the species. Milky juice also contains sugar , starch grains , tannins , glycosides , alkaloids (e.g. in the opium of the opium poppy ), essential oils , waxes and gum resins , organic acids , starch, proteins , enzymes (e.g. papain in the papaya Carica papaya ) in various proportions . and oils either dissolved , emulsified or suspended therein . The presence of emulsified droplets of the water-insoluble organic substances (isoprenoids, oils) causes the milky cloudiness of the milk juice. The milk juice is often toxic because of the alkaloids or glycosides it contains.

About 2000 types of plants contain more or less large amounts of rubber as part of their milky sap, but only about 500 of them are so large that one can speak of plants containing rubber. The rubber content in the milky sap of these plants varies between 1% and 20% of the dry matter (according to Nultsch, see literature). Rubber is in the form of fine particles suspended in the protein-rich matrix. Milky juice containing rubber is also known as latex . Chemically similar to rubber are gutta-percha , balata and chicle .

Anatomy of the milk tubes

Milk tubes (right column of text, lower half)

The milk tubes are branched vascular systems in the organs of the higher plants that form the milky sap and that produce and store the milk sap. Milk tubes were first described by Marcello Malpighi in 1679 .

Depending on the way in which the milk tubes originate, a distinction is made between articulated and non-articulated milk tubes. In addition, a distinction is made between anastomising (forming a network through cross connections) and non-anastomising milk tubes. There are also types with simple milk-sap-carrying cells, the cytoplasm of which is not connected or only connected by plasma bridges (e.g. Parthenium argenteum ). Hevea brasiliensis (rubber tree) and Lactuca serriola (compass plant) have articulated milk tubes . Euphorbia lathyris (cruciferous milkweed) and Ficus elastica (rubber tree) have undivided milk tubes .

Undivided milk tubes grow with the plant from germination and run through the plant body as long, sometimes widely branched tubes. Articulated milk tubes later develop in the mature plant through the fusion of elongated parenchymal cells . The remains of the dissolved transverse walls are only faintly visible in the microscope . Through the formation of lateral bulges, the milk tubes can form lateral branches and connect with other milk tubes (anastomize). This creates a dense network in the plant body. In many plant species, however, the tubes remain without cross connections.

In terms of their physiology and the way in which they function, there is no difference between undivided and articulated milk tubes. The vascular system is polynuclear in both cases. The cell nuclei and mitochondria are pressed against the cell membrane and the cell wall , while the entire cytoplasm is replaced by the milky sap, which contains the remaining organelles (for example ribosomes ). Milky juice is therefore not a dead liquid, but a living cytoplasm.

New formation of milky sap

If the vascular system in a living plant or a fungus fruiting body is damaged, the milky sap with the ribosomes and mitochondria contained in it flows out. The milky sap that escapes hardens in the air and thus closes the wound . Immediately after it has flowed out, the formation of new milky sap begins, which, depending on the amount that has flowed out, is completed after about 2 days. This is only possible because normally some functioning organelles and cell nuclei as well as enzymes remain in the empty milk tubes and can carry out the synthesis of the substances contained in the milk juice.

Importance of the milk juice for the organisms

The meaning of the milk juice was still largely unclear at the time of its discovery. It was initially assumed that the milk tubes were used to carry and store nutrients (Hanstein 1864, Schmalhausen 1877). It later became clear that the sieve tubes in the plants are used for this.

A more likely function of the milk sap is to protect against animal damage. The bitter taste and the toxicity of the substances it contains mean that vertebrates in particular are deterred from eating the milk-containing plants. However , this protection is of no use against the caterpillars of the milkweed hawk ( Hyles euphorbiae ) and the oleander hawk ( Daphnis nerii ). It is possible that protective mechanisms against the toxic ingredients have developed in your metabolism.

Another function of the milk juice is likely to be the protection of organisms from infections . First, the act contained tannins and alkaloids antibiotic , on the other hand the milk juice is at the exit from a wound by a rapid drying up and solidifying wound closure achieved.

The importance of milk juice for humans

Latex extraction

The alkaloids contained in the milk sap of many species have long been used medicinally by humans. In naturopathy, for example, carefully dosed doses of milk juice from milkweed , goose thistle or celandine are used to treat stomach problems, liver weakness and shortness of breath. Externally, the milky sap is used to burn warts and diluted for skin diseases. However, because of the toxicity of the plants mentioned, the application should be left to experts. Latex, the milky sap of the rubber tree ( Hevea brasiliensis ), is called rubber in its dried form and is used to produce rubber . The milky sap of the pear apple tree ( chicle ) is used to produce chewing gum . Gum arabic is obtained from the milky sap of acacia . To obtain the milky sap, the bark of the tree is scored in a V-shape so that the liquid drips out on one side of the trunk and can be collected there in containers. The juice is then concentrated by evaporation or centrifugation and stabilized with ammonia .

Immature seed pods from the latex of the opium poppy is opium won that as the products derived from morphine and heroin found not only as a Narcotic, but also as a painkiller use or even place. However, because of its addictive nature , medicinal use is generally carried out under strict control.

Christ thorn ( Euphorbia millii ) contains tumor- promoting alkaloids in its milk sap . They are only used in small amounts, but as a precaution it is recommended to avoid direct skin contact with the milk sap of this houseplant.

The milky sap of the oriental purging binders served as a drastic laxative because of its glycosidic skammonin content .

literature

  • Wilhelm Nultsch : Allgemeine Botanik , 7th edition, Thieme, 1982
  • Richter, Gerhard: Metabolic Physiology of Plants , 5th Edition, Thieme, 1988
  • Eduard Strasburger : Textbook of Botany , 51st edition 1978
  • Otto Schmeil : Flora von Deutschland , 88th edition, Quelle and Meyer, 1988

Web links

Commons : Latex  album with pictures, videos and audio files

Individual evidence

  1. ↑ Investigation of skin-irritating diterpene esters in milkweed plants (Euphorbiaceae); especially poinsettia and Christ thorn ( memento from January 6, 2001 in the Internet Archive ) (archive.org).