Phytoremediation can be regarded as an excellent method in environmental technologies. In the present scenario, remediation of heavy metals (HMs) contaminated soil has become an important work to be done for the well-being of human and their environment. A balance between elevated metabolic precursors to protective phenylpropanoids and increased biosynthesis of these anthocyanins, flavonoids, and lignin is proposed to play a role in the acclimation of Populus to UV-B radiation and may provide a useful tool in engineering plants as improved bioenergy feedstocks. However, poplar plants with genetic modifications that affect lignin biosynthesis, or natural variants with altered lignin levels and compositions, displayed complex changes in phenylpropanoid metabolites. Noninvasive, ecophysiological measurements using epidermal transmittance and chlorophyll fluorescence as well as metabolite measurements using UPLC-MS generally revealed that the synthesis of anthocyanins, flavonoids, and lignin precursors are increased in Populus upon moderate to high UV-B treatment. were examined for sensitivity or acclimation to UV-B radiation under greenhouse and laboratory conditions. In an effort to explore the relationships between plant lignin levels and composition, the origin of growth elevation, and the hierarchical synthesis of UV-screening compounds, a collection of natural variants as well as transgenic Populus spp. Environmental adaptations by plants also generate a suite of responses for protection against damage caused by UV-B radiation, with plants from high elevations or low latitudes generally displaying greater adaptation or tolerance to UV-B radiation. Flavonoids (phenolic glycosides) and sinapate esters (hydroxycinnamates) have been implicated as UV-B protective compounds because of the accumulation in the leaf epidermis and the strong absorption in the wavelengths corresponding to UV. Plants have evolved to protect leaf mesophyll tissue from damage caused by UV-B radiation by producing an array of UV-absorbing secondary metabolites. These results show that ADF lignins contain significant concentrations of lignin-bound proteins, which renders this method unsuitable to determine genuine lignin. The major fraction of this nitrogen was recovered in amino acids, which corresponded to 14% and 3% protein in ADF lignins of leaves and wood, respectively. C/N analysis revealed the presence of 3.1 and 1.4% nitrogen in ADF lignins of beech leaves and wood, respectively. However, the two calibrations were based on different empirical terms, showing that TGA and ADF lignins did not share the same physical basis for calibration. Both NIRS calibration procedures gave good statistical fits with correlation coefficients close to 1, indicating that TGA and ADF lignin concentrations of beech can be estimated by NIRS with high accuracy. Both ADF and TGA lignin data of beech were used to calibrate near-infrared reflectance spectra (NIRS) for lignin prediction. Leaves of a given species generally contained higher ADF-lignin concentrations than the corresponding stem tissue. In contrast, gravimetrically estimated ADF lignins did not or only moderately correlate with lignins measured with methods based on the UV absorbance of the solubilized lignin degradation products. Lignin concentrations determined in hydrolyzed cell walls of different tissues and species by the AB method showed a good correlation with those obtained by the TGA method and, thus, were convertible. The "lignin" concentration determined with the AB method was strongly dependent on whether or not the cell walls were subjected to alkaline hydrolysis to remove covalently bound aromatic nonligneous components before lignin determination. Each of the three methods estimated a different lignin concentration in a given tissue, except for spruce wood. In each case, cell walls were isolated before lignin determination. Three commonly employed methods for lignin determination, i.e., the thioglycolic acid (TGA), the acetylbromide (AB), and the acid detergent fiber (ADF) method, were compared using leaves and xylem tissue from five species (Nicotiana tabacum, Populus x canescens, Fagus sylvatica, Quercus robur, and Picea abies).
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