Adventitious root system

A primary root system is developed, but is replaced by an adventitious root system. 

In order to determine the rate of recovery, accurate amounts of emetine and cephaeline were added to the medium used for root culture where the adventitious roots of ipecac were cultured for 8 weeks and then extracted as follows twenty ml medium was mixed with 200 pi 10% ammonium hydroxide and 6 ml diethylether in a test tube for 5 min using vortex mixer. Four ml upper layer was accurately taken and concentrated under a stream of nitrogen gas. The extract was dissolved in an appropriate volume of methanol and quantitatively analyzed by HPLC. The HPLC system gave good recovery 104.4% for emetine and 104.8% for cephaeline (Table 6). 

The biosynthesis of the secondary metabolites seems to be related to the differentiation of the cells or plant organs such as shoots or roots [50, 51]. In the section 2, production of isoquinoline alkaloids and tropane alkaloids by adventitious root cultures is described. However, the cultivation of intact plants or their organs is in most cases either phytohormone-dependent or of poor growth, so that these systems are not very useful for industrial purposes [73]. 

In the meantime, the formation of the main alkaloids in C. ipecacuanha under a variety of conditions has been extensively investigated emetine (1) in callus cultures (49) and under the effects of L-tyrosine supplementation (5t)) emetine (1) and cephaeline (2) in Panamanian ipecac (57), in Nicaraguan ipecac (52), in regenerates obtained by clonal propagation (53,54), in tissue cultures (55) and under the effects of exogenous feeding of shikimic acid and L-phenylalanine (55), in cell suspension and excised root cultures (57), in adventitious root cultures (58), and in callus cultures (56,59) and the effects of age and electrokinetic potential (60) ipecoside (7) in the roots (61) and the effect oi Azotobacter, leaf mold, and farmyard manure on alkaloid content (62). In addition, micropropagation systems for C. ipecacuanha have been developed (63-65). 

Despite the small number of studies on the influence of BS on roots, all of the most important experimental root systems, that is, adventitious cutting roots, intact seedling/plant roots, excised root segments and excised cultured roots have already been employed. 

Convenient as root segments may be for some work, their usefulness is diminished by the fact that they represent only a fraction of the root system thus making it difficult to extrapolate to the whole root. Adventitious and seedling roots do not present such problems, but their physical association with shoot tissues can make for difficulties in determining whether roots respond directly to BS or indirectly via primary effects on the shoot. 

Of possible relevance in this respect are the observations that BS and auxin appear to produce opposite effects in root systems whereas they usually act in a similar (but not identical) way on the shoot and commonly show important interactive effects. The most strikingly different effects of these two compounds in roots relate to adventitious root formation in cuttings which is inhibited by BS (24, 30, 31) and promoted by auxin (24), and proton secretion and membrane potential in root segments which are enhanced and hyper-polarized respectively by BS and inhibited and depolarized respectively by auxin (39, 40). These data could suggest either that BS act independently of auxin in roots or that they antagonize... 

It is a general observation that seedlings raised under the influence, for instance, of tetcyclacis or triazoles exhibit a shoot-root-ratio which has shifted in favor of the root. In many cases, root growth is stimulated and longer and thicker main roots can be observed, while the formation of adventitious roots and root hairs is initially inhibited [38]. The formation of an improved root system may be one of the reasons why most of these plants show a better performance at later stages of development. 

The long cultivation times and the low alkaloid yields make these in vitro systems inappropriate for commercial apphcation. Moreover, the supplement of additional phytohormones, essential for support of the adventitious roots growth, could promote the appearance of culture instabilities, manifested by unpredictable alkaloid yields. 

Since ginsenosides are accumulated in the root of the plant, mainly after 6 years of growth, their agricultural production is very expensive. Therefore, ginsenoside production by means of biotechnological alternatives has been extensively studied by a number of researchers, using different plant-derived systems such as callus tissues, cell suspensions, and transformed and adventitious root cultures. 

Hahn EJ, Kim YS, Yu KW, Jeong CS, Pack KY (2003) Adventitious root cultures of Panax ginseng c.v. Meyer and ginsenoside production through large scale biOTeactor system. J Plant Biotechnol 5 1-6... 

After feeding the tips of intact primary roots of Phaseolus seedlings with aqueous solutions of labeled hormones by means of 1 jil-droplets (which were quickly absorbed), percentages of 30, 10, 4, and 1 of the label from kinetin, ABA, GAi, and lAA, respectively, were translocated into the shoot system during the subsequent 24 h. Most of the shoot s kinetin label was detected in the apical bud and primary leaves, although in all cases radioactivity was found in lateral and adventitious roots, about 10% for the ABA and 3% for the other hormones (Hartung 1977). 

This is found on all grasses and cereals, and it is the main root system of most monocotyledons. The primaiy root is soon replaced by adventitious roots, which arise from the base of the stem (Fig. 1.12). These roots can, in fact, develop from any part of the stem, and they are found on some dicotyledons as well (but not as the main root system), e.g. underground stems of the potato. 

As rocks are transformed to soil so a proportion of each element is usually converted to a form which plant roots can absorb. Consequently, most of the elements in the Periodic Table would probably be detected in any plant sample if sufficiently sensitive analytical methods were used. Uptake of an element is no evidence that it plays any role in the development of the plant since a root has no power to reject any soluble element entirely. One must therefore differentiate between those elements which are needed, the essential nutrients, and the rest. The conventional criteria by which the presence of an element is regarded as essential rather than adventitious are these the plant cannot complete its life cycle in the absence of the element the action of the element must be specific in that no other element can wholly substitute for it nor is the element simply involved in beneficially altering the plants root environment the element must be shown to be a constituent of an essential metabolite, or required for the proper functioning of an essential enzyme system or be uniquely involved in maintaining the overall ionic composition of tissue. Table 1-2 lists the elements which are generally accepted as being essential for plants. Major or macronutrients are separated from micronutrients, the latter being present in tissue concentration < 0.1 %. 

Micropropagation systems mentioned previously (Method I and Method II) require two different cultural steps, shoot multiplication and rooting. In the course of tissue culture studies of ipecac, adventitious shoot formation on cultured root had been incidentally found. Therefore, one step micropropagation system of ipecac was established through adventitious shoot formation on the cultured root [14]. 

Polar transport of endogenous lAA was indispensable for the adventitious shoot formation on the cultured roots of ipecac. This micropropagation system can be easily applied to other woody species if detailed mechanism will be elucidated. 

Since secondary metabolite production is generally higher in differentiated tissues, as well as root cultures, the cultivation of shoot cultures for the production of medicinally important compounds has been attempted [20]. Undifferentiated cultures often accumulate secondary metabolites to a lesser extent, or sometimes not at all. For example, a potent antimalarial compound, artemisinin, produced by Artemisia annua has not been observed to accumulate in undifferentiated cultures, while trace amounts have been detected in shoot cultures [21]. In addition, the development of adventitious shoots in liquid cultures has been shown to provide a highly proliferative and rapid growing system amenable to automated inoculation, mechanical separation, control of the medium components, and efficient delivery to the final stage for plant growth and development [13]. There are a number of medicinal plants whose shoot cultures have been studied for their secondary metabolites (Table 89.3). 

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