Root segment

A hierarchical system is the simplest type ofdatabase system. In this form, the var-iou.s data typc.s also called entities (sec figure 5-,3) arc as.signcd. systematically to various levels (Figure 5-5). The hierarchical system is represented as an upside-down tree with one root segment and ordered nodes. Each parent object can have one or more children (objects) but each child has only one parent. If an object should have more than one parent, this entity has to be placed a second time at another place in the database system. 

Macklon, A.E.S. (1975). Cortical cell fluxes and transport to the stele in excised root segments of Allium cepa L. I. Potassium, sodium and chloride. Planta, 122, 109-30. 

Salicylic Acid Absorption. The apical 5 cm of the primary and two seminal roots from each of three plants were out into 1-cm segments to form an experimental unit (ca. 0.08 g). Incubation solution cc ijjtalned 0.5 mM KCl, 0.25 mM CaSOjj, 0.5 mM salicylic acid, 10 nCl/mL [ C]-sallcyllc acid, with 25 mM Tris and 25 mM Mes buffers mixed to obtain pH 6.5. Because the salicylic acid was dissolved in absolute ethanol, the final concentration of ethanol in the incubation solution was 1 (v/v). Root segments were transferred to test tubes containing 10 mL continuously aerated incubation solution. After the predetermined absorption time, segments were collected from the incubation solution by rapid filtration on Whatman No. 2 filter paper. 

Absorption of Salicylic Acid. Excised oat roots absorbed salicylic acid in two distinct phases (Figure 1). Upon exposure to salicylic acid the root segments rapidly absorbed the eompound to attain a concentration of about 0.5 pmole/g of tissue. On the assumption that 1 g of tissue equals 1 mL of tissue, this translates to 0.5 mM salicylic acid inside the tissue, the same concentration as the external solution. This coneentration of salicylic acid was present in the tissue after 1 h and was maintained for over 3 h. By 4 h a second phase of absorption was evident (Figure 1). During the second phase, salicylic acid was absorbed at a greater rate that lasted for at least 24 h. At that time, enough salicylic acid had been absorbed that the eoncentration in the tissue was 8.0 mM. Thus, the tissue accumulated salicylic acid to concentrations greater than that in the external solution. An additional experiment (not shown) showed that the tissue would continue to absorb salicylic acid until the compound was depleted from the external solution. 

Fig. 1. Schematic of root segment preparation used for inoculum conditions of P. ginseng hairy root.

Fig. 3. Growing root segments of P. ginseng hairy root in solid culture for 10 d (A) end part (B) center part.

The uptake of radioactive abscisic acid by radish leaf discs has been described87 and its metabolism (to unidentified compounds) by root segments of Phaseolus coccineus88 and by pea seedlings during and after water stress has been reported.89... 

Fig. 93 Arbuscular mycorrhizal associations in fine roots of adjacent mature forest, secondary forest on abandoned cattle pasture (l6 years old), and active cattle pasture planted with Brachiaria brizantha forage grass. Each data point is the average value for six root samples, with 75 1-cm root segments stained and analyzed per sample following Phillips and Hayman (1970). Percent infection refers to the percent of each root segment s length in which fungal hyphae or arbuscles were visible.

Improved micropropagation of ipecac through adventitious shoot formation on cultured root segments (Method III)... 

Adventitious shoot formation on cultured root segments... 

Table 10. Influence of basal medium on shoot formation from cultured root segments of C. ipecacuanha...

Medium Condition % of shoot formation No. of shoots / segment No. of lateral roots / segment % of establishment to soil... 

Ten cultured root segments were used for each treatment. 

Fig. (24). Shoot formation of cultured root segment a Shoot formation in the dark. Segment was cultured on HF B5 solid medium in the dark for 1 month, b Development of shoots cultured in the dark for 2 months, c Plantlet was further cultured under 16 hr/day light for 1 month, d 17-month old regenerated plant cultivated in a greenhouse. Bars represent I cm (a, b, c) or 5 cm (d).

Table 11. Alkaloid content in the regenerated plants from the cultured root segments and shoot meristem culture...

Light microscopy and SEM were undertaken by the same method described in section 1.4.4. Cross section and SEM of adventitious shoots formed on the cultured root segments are shown in Fig. (25). These observation indicate that shoots were directly formed on the surface of cultured root segments without callus formation as those on the intemode segments. Therefore, the reason for variation in alkaloid contents (Table 11) may not be attributable to the callus formation. 

Adventitious shoot formation occurred when the roots were cultured onto auxin-free medium as mentioned above. Since the decrease of auxin levels seemed to be important for the adventitious shoot formation, the influences of auxin inhibitors on shoot formation on the cultured root segments were investigated. The auxin polar transport inhibitor, 2,3,... 

Table 12. Influences of auxin inhibitors on shoot formation on the cultured root segments...

The roots (ten root segments for each treatment) were cultured on B5 solid medium at 25 °C in the dark. 

The cultured root segments were divided into proximal, distal and newly developed lateral root parts and their endogenous lAA levels were periodically analyzed using enzyme-linked immunosorbent assay (ELISA) kits for lAA (PHYTODETEK iAA, Idetek Inc., USA) according to the procedure of Weiler et al. [39]. The lAA levels in the root segments are indicated in Fig. (26). The lAA levels in the roots cultured on HF B5 medium that initiated shoot formation increased once at day 9 and consequently decreased in both proximal and distal parts. On the other hand, lAA levels in proximal part of the roots cultured in the presence of 0.5 mg/1 TIBA increased along with the culture period. The roots cultured on the MS medium containing 0.5 mg/1 NAA (source for the experiments) accumulated low amounts of lAA and the lateral roots did not accumulate detectable amounts of lAA in all the cases. 

The adventitious root segments (1-2 cm) were inoculated into 50 ml MS liquid medium supplemented with 0.5 mg/1 lAA in a 100 ml Erlenmeyer flask and maintained in the dark on a rotary shaker (100 rpm) at 25 C. The roots ca. 30 mg fresh weight) were subcultured at four weekly intervals in order to obtain sufficient materials for experiments. To examine the effect of auxins in root culture, roots ca. 30 mg fresh weight) were inoculated into 50 ml MS liquid medium supplemented with various concentrations of auxins under the conditions described above. Growth and alkaloid contents were measured after certain culture periods. 

Fig. (45). Shoot regeneration on the adventitious and hairy root segments of Duboisia hybrid.

The root segments grown in MS liquid media were cultured on 1/2 MS solid medium containing various concentrations and combinations of IAA and BA for 7 weeks at 25 °C under 16 hr/day light. Three segments were used for each treatment. 

Hairy root segments ca. 1 cm) were placed onto MS solid medium either with lAA (0.1-0.5 mg/1) and/or BA (0.5-1 mg/1) or without... 

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. 

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