Horseradish (Armoracia rusticana) hairy roots were established by transformation with the Ri plasmid T-DNA in Agrobacterium rhizogenes ATCC 15834. To elucidate effects of light and sugar signals on differentiation of adventitious shoots, horseradish hairy roots were cultured in phytohormone-free LS medium in the dark and light conditions. Adventitious shoots were formed in the presence of 1% (W/V) sucrose in the light but not formed in the dark condition. And long term exposure of horseradish hairy roots to light more than 3 days was important to induce the formation of adventitious shoots in the negligible condition of sugar-signaling. On the other hand, adventitious shoots were formed in the presence of 3-10% (W/V) sucrose in the dark as well as in the light condition. These results showed both light and sugar signals were involved in differentiation of adventitious shoots in horseradish hairy roots.

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Horseradish (Armoracia rusticana) hairy-root clones AR182 and AR450 were used to examine the capabilities for differentiation of adventitious shoots from root segments. When horseradish hairy roots were cultured in phytohormone-free LS medium in the light condition, adventitious shoots were formed in AR450 but not formed in AR182. To elucidate effects of phytohormones on differentiation of adventitious shoots in AR182, hairy roots were cultured in LS medium containing naphthaleneacetic acid (NAA) and benzyladenine (BA) in the light condition. A large number of adventitious shoots were formed in LS (10^-6M NAA) and LS (10^-7M NAA and 10^-7 M BA) in AR450. But adventitious shoot was not formed in AR182 even in the presence of NAA and BA. These results showed that the adventitious shoot formation was strongly repressed in AR182.

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The associations of tree species with physical (edaphic and/or topographic) habitats in species-rich tropical forests, and interspecific differences in their habitat association are commonly observed. One would therefore expect tree species to have developed numerous anatomical and physiological adaptations to specialized habitat conditions in a niche where the species regenerate preferentially. A wide variation among seedlings of tropical tree species in the morphology of roots has been observed. The variation in root architecture and allometry of tropical tree seedlings may be explained by trade-off between depth growth for the uptake of water which increases with depth and horizontal growth around the soil surface for the uptake of nutrients which tend to lie close to the soil surface. Therefore, it is hypothesized that architectural and allometric variations in roots generate competitive advantage of a species over counterpart competitors in a habitat where the species regenerates preferentially and in turn lead to equilibrium coexistence of tree species in forest communities.

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Horsenettle (Sonalum carolinense L.), a clonal perennial is native of the southern US, has been increasing as a serious weed in Japan. Control of the horsenettle is difficult because of clonal reproduction by its extensive root system. Therefore, whole structure of the root system, shoot emergence and its control mechanism within a clone, allocation pattern and strategy of vegetative reproduction were investigated. 1. The root system is composed of horizontal and vertical roots that are clearly divided. 2. Shoot emergence period is limited during one and half months of the spring because of its intensive intra-clonal control. 3. The shoots spread slower than the root system in a clone. 4. The root system has priority over other organs in dry matter allocation. 5. Dry matter allocation to the inside of a clone is higher than the outside in the shoots but not in the root system. Consequently, strategy of vegetative reproduction of horsenettle is conservative and tolerant to disturbance and stress. Therefore, eradication of horsenettle is not the purpose but the result of long and adequate control.

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