Bonhomme F, Kurz B, Melzer S, Bernier G, Jacqmard A
Laboratory of Plant Physiology, University of Liège, Sart Tilman, B4000 Liège, Belgium.
Plant J. 2000 Oct;24(1):103-11. doi: 10.1046/j.1365-313x.2000.00859.x.
In plants of Sinapis alba induced to flower by one long day, the MADS box gene, SaMADS A, is expressed initially in the central corpus (L3 cells) of the shoot apical meristem (SAM), about 1.5-2 days before initiation of the first floral meristem. We have combined a physiological approach by testing the effects of three putative floral signals on SaMADS A expression in the SAM of S. alba plants with a transgenic approach using Arabidopsis thaliana plants. A single application of a low dose of a cytokinin or a gibberellin to the apex of vegetative S. alba plants is capable of mimicking perfectly the initial effect of the long day on SaMADS A transcription. A treatment combining the two hormones causes the same activation but seems to enhance the level of SaMADS A expression. A sucrose application to the apex of vegetative plants is, on the contrary, unable to activate SaMADS A expression. None of these chemicals, alone or combined, is capable of causing the floral shift at the SAM. Since the constitutive expression of SaMADS A leads to precocious flowering in A. thaliana and antisense expression of a fragment of the A. thaliana homologue AGL20 leads to a delay in flowering time, these results are consistent with SaMADS A activation being an intermediate event in a cytokinin- and/or gibberellin-triggered signal transduction pathway that is involved in the regulation of floral transition in S. alba.
在经一个长日照诱导开花的白芥植株中，MADS盒基因SaMADS A最初在茎尖分生组织（SAM）的中央原体（L3细胞）中表达，大约在第一个花分生组织起始前1.5 - 2天。我们将通过测试三种假定的花信号对白芥植株SAM中SaMADS A表达的影响的生理学方法，与使用拟南芥植株的转基因方法相结合。向营养生长的白芥植株顶端单次施用低剂量的细胞分裂素或赤霉素，能够完美模拟长日照对SaMADS A转录的初始影响。两种激素联合处理会产生相同的激活作用，但似乎会提高SaMADS A的表达水平。相反，向营养生长植株顶端施用蔗糖不能激活SaMADS A的表达。这些化学物质单独或联合使用，均不能在SAM处引起花转变。由于SaMADS A的组成型表达导致拟南芥提前开花，而拟南芥同源物AGL20片段的反义表达导致开花时间延迟，这些结果与SaMADS A的激活是细胞分裂素和/或赤霉素触发的信号转导途径中的一个中间事件一致，该信号转导途径参与白芥花转变的调控。
