Functional analysis of dwarf genes located in T-DNA of Ri plasmids and its application to plant breeding

菊苣花芽分化需要低温长日照处理。然而，用Ri质粒的T-DNA转化的菊苣植株在长日照条件下不经低温处理就表现出开花。在转Ri质粒T-DNA上的rol C基因的菊苣植株中也观察到类似的不经低温处理的花芽形成现象。用赤霉素、反赤霉素、细胞分裂素和乙烯等植物生长调节剂处理未转化的菊苣植株，赤霉素（GA_3）诱导茎伸长，但不诱导花芽分化。抗赤霉素（S-3307，一种有效的赤霉素生物合成抑制剂）对菊苣花芽分化的诱导频率较低，而且当用GA_3处理转Ri T-DNA的菊苣植株时，不能观察到花芽的形成。这些结果表明，Ri T-DNA可能具有抑制赤霉素生物合成或抑制赤霉素活性的生理功能。转化植株和正常植株的赤霉素主要为GA_1，转化植株中GA_1的含量低于正常植株的1/100。这一结果表明，一些生理反应（包括矮化），特别是在植物中观察到的Ri T-DNA转化诱导内源赤霉素含量的减少转化植物。

It is well known that Cichorium intybus requires low temperature and long day treatments for the flower bub differentiation. However, Cichorium plants transformed with T-DNA of Ri plasmid exhibited flower formation without low temperature treatment under a long day condition. Similar phenomenon of flower bud formation without low temperature treatment was also observed in Cichorium plants transformed with single rol C gene located on the T-DNA of Ri plasmid. When not-transformed (normal) Cichorium plants were treated with some plant growth regulators, such as gibberellin, anti-gibberellin, cytokinin, and ethylene, gibberellin (GA_3) induced the stem elongation, but not the flower bud differentiation. On the other hand, anti-gibberellin (S-3307, a potent inhibitor of gibberellin biosynthesis) induced the flower bud differentiation with low frequency.Moreover, when Cichorium plants transformed with Ri T-DNA were treated with GA_3, flower bud formation could not be observed. These results indicate that a possible physiological function of Ri T-DNA is an inhibition of gibberellin biosynthesis or a suppression of gibberellin activity).Qualitative and quantitative analyses of endogenous gibberellin in Atropa belladonna transformed with Ri T-DNA were carried out by using radio-immunoassay with monoclonal antibodies against some gibberellins. The major gibberellin in the transformed and normal plants was GA_1, and the contents of GA_1 in the transformed plants was less than 1/100 as compared to that of the normal plants. This result suggests that some physiological responses (including dwarfism) observed specifically in plants transformed with Ri T-DNA were induced by the decrease of endosenous gibberellin contents in the transformed plants.