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Genetic differentiation of European black poplar (Populus Nigra L.) clones and populations with respect to some enzymes involved in biosynthesis of cellulose and lignin

Taşkıran, Bircan
The European black poplar, (Populus nigra L.) is ecologically and economically important fast-growing trees. Its wide distribution range in northern hemisphere, easy vegetative propagation, rapid growth rate and hybridization ability, and also its biomass source potential make European black poplar a perfect candidate for lignocellulosic biomass production. In this study, specific activities of two important cellulose related (SuSy and UGPase) and three lignin pathway related (PAL, 4CL, and CAD) enzymes, were evaluated in natural P. nigra clones. In addition to cellulose and lignin related enzyme activities, cellulose, lignin, and glucose contents, as well as height and diameter of clones were examined to explore genetic variance components, heritability of traits, and relationships between these traits. Also, clones with lignocellulosic potential were identified to be used for future breeding studies and industrial applications. As a total, 285 clones (genotypes) represented by 4 ramets and replicated twice are used for the study. The results of our study indicated that the great portion of total variation was due to clonal variation ranging from 33.0% (in UGPase) to 64.1% (in glucose). Moderate to high clonal heritabilities were estimated for traits ranging from 0.50 (in UGPase) to 0.80 (in glucose). All lignin related traits showed moderate heritabilities ranging from 0.53 (in CAD) to 0.61 (in PAL). Number of clones with desired cellulose and lignin properties were found. One of these clones, 62160 was among the highest 12 clones regarding UGPase, SuSy, cellulose, height, and diameter, but it was also among the lowest 12 clones with respect to PAL and CAD activities. Phenotypic correlations of cellulose content with SuSy (rp=0.184) and UGPase (rp=0.160) were low, but significant. Although PAL, 4CL, and CAD were positively correlated with each other, surprisingly there were no significant relationships detected between lignin content and these enzymes. The positive correlation among these phenylpropanoid pathway enzymes clearly demonstrated the flux of the substrate into the pathway, but no relationships between lignin content and them suggested that there might be more complicated regulations in the pathway which leads to change in lignin composition rather than lignin deposition.