科研之友
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摘要
We investigated the alteration in l-ascorbate (AsA, reduced form) content and the expression pattern of its related genes during the phase transition in Oncidium orchid. During the vegetative growth, a high H(2)O(2) level was associated with a high content of the reduced form of AsA. During the bolting period, the AsA content and H(2)O(2) level were greatly reduced in parallel with increased expression of OgLEAFY, the gene encoding a key transcription factor integrating different flowering-inducing pathways. This observation suggests that reduced AsA content, due to it having been consumed in scavenging H(2)O(2), is a prerequisite for mediating the phase transition in Oncidium. A survey of the AsA biosynthetic pathway revealed that the gene expression and enzymatic activities of the products of relevant genes of the galacturonate (GalUA) pathway, such as polygalacturonase (OgPG), pectin methylesterase (OgPME) and galacturonate reductase (OgGalUAR), were markedly decreased during the bolting period, as compared with during the vegetative stage. However, the genes whose products were involved in the SmirnoffWheeler pathway retained a similar expression level in the two growth stages. The data suggested that OgPME of the GalUA pathway was the pivotal gene in regulating AsA biosynthesis during the bolting period. Further elucidation by overexpressing OgPME in Arabidopsis demonstrated a considerable increase in AsA content, as well as a resulting delayed-flowering phenotype. Our results strongly imply that the reduced level of AsA, regulating bolting for phase transition, resulting in part from its consumption by scavenging H(2)O(2), was mainly caused by the down-regulation of the GalUA pathway, not the SmirnoffWheeler pathway.
- 出版日期2009-5
