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

众所周知，菊苣的花芽分化需要低温和长时间的处理。而经Ri质粒T-DNA转化的菊苣在长日照条件下，不经低温处理也能开花。在Ri质粒T-DNA上单个rol - C基因转化的菊苣植株中，也观察到类似的不经低温处理的花芽形成现象。赤霉素、抗赤霉素、细胞分裂素、乙烯等植物生长调节剂对未转化（正常）菊苣的茎伸长有诱导作用，而赤霉素（GA_3）对花芽分化无诱导作用。另一方面，抗赤霉素（S-3307，一种有效的赤霉素合成抑制剂）诱导花芽分化的频率较低。经Ri T-DNA转化的菊苣植株经GA_3处理后，花芽未形成。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。采用单克隆抗体对部分赤霉素进行放射免疫分析，对经Ri T-DNA转化的颠茄内源赤霉素进行定性和定量分析。转化植株和正常植株的赤霉素主要以GA_1为主，且与正常植株相比，转化植株的GA_1含量不到1/100。这一结果表明，Ri T-DNA转化植株的一些生理反应（包括矮化）是由转化植株内源性赤霉素含量的减少引起的。

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.