PARENT SESSION
Posters P6D Crop photosynthesis, agricultural biotechnology. Abstracts (742-753)

Effects of exogenous gibberellin on the biomass production of lombardy poplar. Tomohiro Igasaki^*,1, Kenji Shinohara¹, ¹ Forestry and Forest Products Research Institute, Tsukuba, Japan

ABSTRACT- Gibberellins (GAs) are essential endogenous regulators of growth and developmental processes throughout the plant life cycle. We are interested in genetic engineering of the biosynthesis of GAs to control the growth of lombardy poplar (Populus nigra). Before molecular biological approach, we studied the effects of GA₃ on the biomass production and carbon fixation of lombardy poplar. Clonal materials were treated with 15 M, 45 M or 150 M GA₃, or left untreated, for five weeks. The rates of increases in the height and the diameter of shoots and the numbers of nodes were increased by all treatments with GA₃. Total dry-matter production and the dry weights of terrestrial parts increased with increases in the concentration of GA₃, while dry weights of roots decreased. The net photosynthetic rate and the levels of Chl and carotenoids in mature leaves decreased at 150 M GA₃, but the level of anthocyanin was not significantly different in all plants. An analysis of wood anatomy revealed that the numbers of epidermal and pith cells and the number of xylem fiber cells increased after all treatments and that GA₃ at 45 M and 150 M stimulated the vertical elongation of xylem fibers. But the dimensions of epidermal, pith and xylem fiber cells were unaffected by the treatments. The relative levels of monosaccharides, the lignin content of cell walls, and the ratio of syringyl aldehyde to vanillin in lignin residues were also not significantly affected by the treatments. The internal level of GA₃ increased markedly after the treatments, while the levels of GA₁, GA₂₀, GA₄, GA₉ and GA₅ significantly decreased. Thus, exogenous GA₃ has a positive effect on the growth of lombardy poplar at appropriate concentrations. We have also isolated the genes for enzymes of GAs biosyntheses, and examined their expression and functions in lombardy poplar.

KEY WORDS: biomass, Populus, gibberellin, poplar