Translocation,

Results of some of the grafting experiments described in the previous section sug t strongly that alkaloids, in particular those of the.nicotine and tropane groups, are carried from the root and distributed throughout the aerial parts of the plant. The obvious agent of transport is the transpiration stream, and its participation has been confirmed by Dawson s (82) observations on the sap bleeding from cut stumps of Connecticut tobacco plants. The sap could be seen to exude from the xylem only and contained 

nicotine per ml. The sap exuding from the cut stumps of Datura stramonium plants gives a good Vitali-Morin reaction for tropane alkaloids (96). The alkaloids themselves, as distinct from soluble precursors, are therefore moved by this mechanism. 

It is a general observation that aging leaves lose at least a proportion of their alkaloids while attached to the plant. This could be due to a slow evacuation of soluble alkaloid salts into the stem. It could also be due to breakdown in situ, either with or without subsequent transport, of the degradation products. Detached belladonna leaves do break down their alkaloids after a more or less prolonged period of detachment, and similar destruction of nicotine has been observed by Mothes in old tobacco leaves, though Vickery et al. failed to observe it in leaves which were, perhaps, younger (99). 

It is obvious that evidence for or against the movement within the symplast of alkaloids, as such, is still inconclusive. Movements accompanied by partial breakdo vn with subsequent resynthesis, as happens with proteins and polysaccharides, would also explain the above observations, but such a process appears chemically improbable in some instances. 

---

C2H4N4. A translocated herbicide, m.p. 157-159 C, used as a non-selective herbicide on fallow land or in established orchards. 

MCPB, 4-(4-chloro-2-methylphenoxy)-butyric acid, CiiHisClOj. A compound in itself harmless to plants, but when absorbed and translocated in the cells, CnHuClOs is converted to a powerful herbicide, and results in the death of the plant. Acts as a selective weedkiller. Other butyric acid derivatives used commercially are 2,4-Dg and 2,4,5-Tb, the butyric acid analogues of 2,4-D and 2,4,5-T. ... 

CaH24N.,03P2,(Me2N)2P(0)0P(0)(NMe2)z. It is not highly toxic to insects when used as a contact insecticide, but is readily absorbed by the roots and leaves of plants and translocated in the sap, so that the plant becomes toxic to species feeding on it. 

The concentration of alkaloids, as well as the specific area of occurrence or localization within the plant or animal, can vary enormously. Thus the amount of nicotine [54-11-5] (21), C2QH24N2, apparentiy synthesized ia the roots of various species of JSHcotiana and subsequentiy translocated to the leaves varies with soil conditions, moisture, extent of cultivation, season of harvest, etc and may be as high as 8% of the dry leaf, whereas the amount of morphine (2, R = H) ia cerebrospiaal duid is of the order of 2 to 339 fmol/mL (23). 

On ornamental plants CCC is appHed to a2aleas, geraniums, and hibiscus (Hibiscus sp] to make compact plants, and to poinsettias to reduce stem height and increase the red color of the bracts. A considerable amount of work has been carried out on cereals with CCC to reduce stem length and inhibit lodging. In Europe, the effect of CCC on shortening the culms of cereals is dependent upon the genotype. It has been demonstrated that the effect is as follows wheat > triticale > durum wheat > rye > oats > barley > corn = millet = rice (37). In barley, culms are initially inhibited but later the plant overcomes the inhibition (37). This has been attributed to poor assimilation, translocation, and rapid breakdown in wheat (38). 

Inabenfide. [4-Chloro-2-(a-hydroxybenzyl)]-isonicotonanilide) [82211 -24-3] (Inabenfide) (32) is not for use in the United States, but is used in other countries to inhibit the growth of rice plants. The compound is appHed to the soil 40—60 days prior to the heading up of plants, where it is absorbed through the roots and translocated throughout the stem. It inhibits the elongation of the lower intemodes and this stops lodging. It is extremely toxic to fish. 

Biorational approaches have proven useful in the development of classes of herbicides which inhibit essential metaboHc pathways common to all plants and thus are specific to plants and have low toxicity to mammalian species. Biorational herbicide development remains a high risk endeavor since promising high activities observed in the laboratory may be nullified by factors such as limitations in plant uptake and translocation, and the instabiHty or inactivity of biochemical en2yme inhibitors under the harsher environmental conditions in the field. Despite these recogni2ed drawbacks, biorational design of herbicides has shown sufficient potential to make the study of herbicide modes of action an important and growing research area. 

In this type of activation, which occurs in both animal and plant tissues, the original insecticide is relatively stable and can be translocated through plant tissues without destmctive hydrolysis until the oxidation has occurred, which then makes the insecticide both highly toxic and relatively unstable so that it rapidly is hydroly2ed to nontoxic products. 

Genetic Control. Manipulation of the mechanisms of inheritance of the insect pest populations has occurred most successhiUy through the mass release of steri1i2ed males, but a variety of other techniques have been studied, including the environmental use of chemostetilants and the mass introduction of deleterious mutations, eg, conditional lethals and chromosomal translocations (58 ndash 60) (see Genetic engineering). 

Metabolic Functions. Chromium (ITT) potentiates the action of insulin and may be considered a cofactor for insulin (137,138). In in vitro tests of epididymal fat tissue of chromium-deficient rats, Cr(III) increases the uptake of glucose only in the presence of insulin (137). The interaction of Cr(III) and insulin also is demonstrated by experimental results indicating an effect of Cr(III) in translocation of sugars into ceUs at the first step of sugar metaboHsm. Chromium is thought to form a complex with insulin and insulin receptors (136). 

Excitation of smooth muscle via alpha-1 receptors (eg, in the utems, vascular smooth muscle) is accompanied by an increase in intraceUular-free calcium, possibly by stimulation of phosphoUpase C which accelerates the breakdown of polyphosphoinositides to form the second messengers inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 releases intracellular calcium, and DAG, by activation of protein kinase C, may also contribute to signal transduction. In addition, it is also thought that alpha-1 adrenergic receptors may be coupled to another second messenger, a pertussis toxin-sensitive G-protein that mediates the translocation of extracellular calcium. 

Ethylene oxide has been shown to produce mutagenic and cytogenic effects in a variety of test systems (226). An increased frequency of chromosomal aberrations in peripheral lymphocytes of monkey exposed to ethylene oxide for 104 weeks has been reported (240). In mice, it is an effective inducer of chromosome breaks leading to dominant-lethal mutations. In addition, ethylene oxide has been shown to induce heritable effects in the heritable translocation test conducted in mice exposed to ethylene oxide by inhalation (241,242). In this study, male mice were exposed to ethylene oxide ranging from 165 to 300 ppm for 6 h per day 5 or 7 days/week for 8.5 weeks. Ethylene oxide has also been shown to bind to proteins (243) as well as to DNA (244). Several studies on ethylene oxide-exposed workers have demonstrated an increased incidence of chromosomal aberrations and sister chromatid exchanges the relevance of such effects to human health evaluation is currendy uncertain. 

---