Latex vessels

Alkaloids are found in all parts of the plant, especially in bark, leaves, root and fruits. Sometimes the alkaloids are found in certain cell-types of tissues, e.g. the opium alkaloids are found specifically in the latex vessels of the poppy fruit or capsule. 

Errera (18) drew attention to four tendencies of alkaloid distribution. Concentration is normally high in (o) very active tissues, growing fruits, etc. (6) epidermis, piliferous layer, and the layers just below them (c) vascular sheaths and other perenchyma adjoining and penetrating the vascular tissue (d) latex vessels, where present. 

Rubber formation takes place in the latex vessels and all intermediates of the pathway occur there. The latex of Hevea and many other plants consists of multinucleate protoplasm in extensively anastomosed duct systems of laticifers (Loomis and Croteau, 1980). Electron microscopy of laticifers from several plants families has shown that latex is a highly specialized cytoplasm containing typical structures such as nuclei and mitochondria, endoplasmic reticulum, and ribosomes, as well as polyisoprene and resin particles. Latic-... 

In Hevea brasiliensis, rabber is largely formed and stored in the bark, in rings of latex vessels interspersed with the sieve tubes of the secondary phloem of the trank, branches, or roots. Laticifers also are present in the leaves, flowers. 

NR latex flows out from the latex vessels of NR trees after tapping. Best NR yield can be obtained for tapping at around 2 am. The latex vessels beeome plugged with particles after clotting is initiated by the flow of NR latex after several hours. When the cut is reopened on the following day, NR latex flows out again. The NR latex is collected daily for further processes. The production... 

Rubber is obtained from the latex of Hevea hrasiliensis where it occurs in a system of specialized, connected cells, the latex vessels. Latex contains rubber particles with a diameter of up to 3 fxm. The rubber particles are suspended in the liquid cell plasm along with nuclei, mitochondria, ribosomes, soluble enzymes etc. 

Latex, under certain conditions, is able to synthesize rubber even when removed from the latex vessels. While formation of isopentenyl pyrophosphate takes place in the latex fluid, polymerization to rubber takes place on the surface of rubber particles. It is catalyzed by a polymerase located at the boundary between the particles and the aqueous phase. The rubber molecules formed vary in size from 500 to 5000 isoprene units. 

Nordal,A., Benson,A.A. Phorbic acid biosynthesis in the latex vessel system of Euphorbia. Plant Physiol. 44,78-84 (1969)... 

Figure 6.29a. A longitudinal ultrathin section of part of a latex vessel in a Papaver somni-femm capsule showing smooth and granulated alkaloidal vesicles. Glutaraldehyde/osmium tetroxide fixation with lead citrate poststaining and Epon embedding x 10,000 reduced 25% for reproduction.

Latex is obtained from the tree by a process called tapping. Near the cambium layer in the bark are the latex vessels, a network of capillary tubes that occur in all parts of the tree but are concentrated in the bark. Here the plant food is changed into rubber hydrocarbon. A cut is made into the thin lay of lactiferous vessels, the cambium lay being carefully avoided. Latex exudes from this cut and is collected. 

Tapping is done in the early morning hours when flow is at a maximum. After about 5 hours, the flow rate decreases, the cut latex vessels start to choke with coagulated latex, and the flow stops. At the time of tapping, a small amount of ammonia is placed in the cup to prevent premature coagulation. 

In poppy plants morphinan alkaloids are primarily accumulated in latex which in turn is contained in structurally and physiologically specialized cells, laticifers. Roberts et al. (1983 and references therein) demonstrated that 1000 g and supernatant fractions of the latex are required for alkaloid biosynthesis and that a subpopulation of dense organelles of the 1000 g sediment have a function as a storage compartment for alkaloids. Morphinan alkaloid production with poppy cell cultures, therefore, would appear to require the concurrent differentiation of latex vessels. The high levels of alkaloid accumulation would thus appear to be intriguingly correlated with the formation of latex and latex vessels. 

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