Changes in the spectral pattern of selenium accumulation in Coleus blumei and the effects of chelation.

Chemically enhanced phytoremediation has been proposed as an effective approach to remove heavy metals from contaminated soil through the use of high biomass production plants. This study investigated changes in the spectral pattern of selenium (Se) accumulation in Coleus blumei Benth. (coleus) plants grown in hydroponics with 1.0 mg/l sodium selenite (Na2SeO3) and the effects of (S,S)-ethylenediamine disuccinic acid (EDDS) thereon through X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDXS) and Fourier transform infrared (FTIR) spectroscopy analyses. When EDDS concentrations were in the range of 0-1.0 mmol/l, Se content increased significantly; however, at EDDS concentrations above this range, the symptoms of Se toxicity were alleviated in coleus leaves. Application of EDDS over 1.0 mmol/l significantly decreased total Se uptake in the leaves and roots of the plants. The powder diffraction patterns of the roots and leaves displayed sharp crystalline peaks, which were characteristic of an organic molecule with crystallinity. Our results revealed the presence of high amounts of C, O, Mg, Al, Si, K and Ca in the roots and leaves under Se-induced stress with different concentrations of EDDS. There were no changes in the chemical compositions of the roots and leaves, but the contents were influenced by Se-induced stress and EDDS treatment. This study demonstrated the importance of applying XRD, EDXS and FTIR methods toward a more comprehensive understanding of the mechanisms of EDDS-induced Se accumulation in plants.

Genetic elicitation by inducible expression of ß-cryptogein stimulates secretion of phenolics from Coleus blumei hairy roots.

The accumulation of phenolic compounds in plants is often part of the defense response against stress and pathogen attack, which can be triggered and activated by elicitors. Oomycetal proteinaceous elicitor, ß-cryptogein, induces hypersensitive response and systemic acquired resistance against some pathogens. In order to test the effect of endogenously synthesized cryptogein protein on phenolic compounds accumulation in tissue, and secretion into the culture medium, Coleus blumei hairy roots were generated. Agrobacterium rhizogenes was employed to insert synthetic crypt gene, encoding ß-cryptogein, under the control of alcohol-inducible promoter. The expression of ß-cryptogein, in C. blumei hairy roots, was controlled by application of 1% and 2% ethanol, during 21 days induction period. Ethanol-induced expression of ß-cryptogein caused significant decrease of soluble phenolics and rosmarinic acid (RA) in hairy root lines and increase of phenolics, RA and caffeic acid in culture medium. These data suggest that ß-cryptogein might be a potential regulatory factor for phenolics secretion from the roots.

Exploration of the ability of Coleus blumei to accumulate aluminum.

In this study, the capacity of an ornamental species (Coleus blumei) to extract and accumulate aluminum was evaluated. The analyzed parameters were amount of soluble aluminum, radical growth, tolerance rate, bioaccumulation factor, and tissues aluminum concentration. The main limiting factor for aluminum accumulation is the availability of the metal. However, Coleus blumei can grow and accumulate up to 1445.7 mg kg(-1) of aluminum dry base. This plant can play an important role in the treatment of polluted water with metals, since it can grow in conditions with a pH of around 4.8. The aluminum tolerance rate showed for this plant ranged between 18.8% and 25%. Therefore, this species behaves as a non-accumulator, even though the bioaccumulation factor was 3098.5 L kg(-1).

Influence of growth regulators and sucrose concentrations on growth and rosmarinic acid production in calli and suspension cultures of Coleus blumei.

Rosmarinic acid, which is reported to have adstringent, antibacterial, antiviral and antioxidant activities, is one of the most prominent secondary compounds in Coleus blumei (Lamiaceae). Rosmarinic acid (RA) production in different hybrids of C. blumei was estimated by HPLC. Conditions for HPLC were as follows: column, 150 x 4.6 mm; solvent system, methanol -0.1% phosphate (45 : 55); flow rate, 0.9 mL/min; detection: 325 nm. Two out of four hybrids of C. blumei (hy1; hy2) contain better rosmarinic acid production (0.9 and 1.0% dry weight, respectively) and the leaves have the highest rosmarinic acid production, followed by stems and roots. The hydroxyphenylpyruvate reductase (HPPR) gene expression levels were analysed by semi-quantitative RT-PCR. Hy3 shows highest level of HPPR gene expression out of four hybrids on genotype-specific patterns, and stems represent the highest level of HPPR gene expression among leaves, roots and stems. This was probably a result of the fact that the RA biosynthetic pathway was regulated by interactions of several enzymes necessary for biosynthesis. The explants from the hy1 leaves were used in subsequent studies on the effect of different growth regulators (2.0 mg L(-1) 6-benzyl-aminopurine (6-BA), different 2,4-dichlorophenxyaretic acid (2,4-D) and alpha-naphthaleneacetic (NAA) concentrations) and sucrose contents (1, 2, 3, 4, 5 or 6%) on culture growth and rosmarinic acid accumulation. On the effect of different growth regulators, the best result is obtained when the B5-medium supplemented is with 2.0 mg L(-1) 6-BA, 0.5 mg L(-1) NAA, 0.8 mg L(-1) 2,4-D and 2% sugar, and solidified with 0.8% agar. In this case, both growth index and rosmarinic acid accumulation reach a maximum, which is 49.7 and 25.3% (dry weight), respectively. The optimal medium for suspension culture growth contains 2.0 mg L(-1) 6-BA, 0.5 mg L(-1) NAA, 0.8 mg L(-1) 2,4-D, 600 mg L(-1) inositel and 2% sugar, and the rosmarinic acid production is 1.7% (dry weight). The rosmarinic acid accumulation is enhanced by the sucrose concentrations. When the sucrose content is 6%, the calli and cell culture accumulate 33.7% (dry weight) and 10.1% (dry weight) rosmarinic acid, respectively. Higher sucrose content (>or=5%) has a negative influence on culture growth. B5-medium supplemented with 2.0 mg L(-1) 6-BA, 0.5 mg L(-1) NAA, 0.8 mg L(-1) 2,4-D, 4% sugar and 0.8% agar is best for both culture growth and rosmarinic acid accumulation. On the basis of the above results, we can establish a two-phase culture system by calli of C. blumei for the biosynthesis of RA. In the growth phase, the calli grow well, but with lower RA production in a modified B5-1A medium with 2% sucrose. The calli are then subcultured to B5-1A medium with 6% sucrose where the calli start to accumulate RA, but grow slowly.

Changes in antioxidant potential and sink-organ dry matter with pigment accumulation induced by hexaconazole in Plectranthus forskholii Briq.

An investigation was conducted in Plectranthus forskholii by giving it different concentrations (10, 15, 20, 25, and 30 mg L(-1)) of hexaconazole, a fungicide cum plant-growth regulator, in order to find out its effects on growth, pigment composition, and antioxidant potential. The treatments were given as soil drenching on different growth stages. All the concentrations of hexaconazole used significantly decreased the stem length and leaf area, whereas side branches, fresh and dry matter content, photosynthetic pigments, and antioxidant potential were increased. The number of tubers, length and girth of tubers, fresh and dry weight of tubers and tuber pigments were found to be the highest at a 25 mg L(-1) concentration of hexaconazole. Hexaconazole application at 25 mg L(-1) concentration was found to be more effective than 10, 15, 20, 25, and 30 mg L(-1) in promoting fresh and dry weight of root tuber over 165 days after planting. The pigments like chlorophyll, carotenoid; anthocyanins, xanthophylls and antioxidants such as ascorbic acid, reduced glutathione and total phenol were significantly increased under hexaconazole treatment when compared to untreated control plants.

Potential application of urea-derived herbicides as cytokinins in plant tissue culture.

Various urea-derived herbicides and different cytokinin analogues were used to determine their effects on callusing response and shoot regenerating capacity of alfalfa (Medicago sativa L.) and Coleus (Coleus forskohlii Briq.). The herbicides monuron and diuron evoked profuse callusing response from Coleus leaf segments and alfalfa petiole explants on Murashige and Skoog medium. Shoot regeneration by monuron (2.0 mg/l) showed a maximum of 3 multiple shoots both in alfalfa and Coleus with a frequency of 92% and 75%, respectively. Whereas diuron (0.5 mg/l) showed a high frequency of shoot regeneration (89%)with a mean number of 5 shoots in alfalfa, in C.forskohlii, the frequency of regeneration was 90%with a mean number of 6 shoots. Diuron with two chloride groups in the phenyl ring showed significantly higher cytokinin-like activity than single chloride substitution monuron. This study demonstrates the potential use of monuron and diuron as cytokinins in plant tissue culture.