Department of Applied Biology, University of Helsinki, Finland.
Ann Bot. 2010 Nov;106(5):697-707. doi: 10.1093/aob/mcq174. Epub 2010 Aug 26.
Timothy is a long-day grass species well adapted for cultivation in northern latitudes. It produces elongating tillers not only in spring growth but also later in summer. As the quantity and quality of harvested biomass is dictated by canopy architecture and the proportion of stem-forming flowering tillers, the regulation of flowering is of great interest in forage grass production.
Canopy architecture, stem morphology and freezing tolerance of vernalized timothy were investigated in greenhouse and field experiments. The molecular control of development was examined by analysing the relationship between apex development and expression of timothy homologues of the floral inducer VRN1 and repressor VRN2.
True stem formation and lignification of the sclerenchyma ring occur in both vernalized and regrowing stems irrespective of the developmental stage of the apex. The stems had, however, divergent morphology. Vernalization enhanced flowering, and the expression of the VRN1 homologue was elevated when the apex had passed into the reproductive stage. High VRN1 homologue expression was not associated with reduction in freezing tolerance and the expression coincided with increased levels of the floral repressor VRN2 homologue. Field experiments supported the observed linkage between the upregulation of the VRN1 homologue and the transition to the reproductive stage in vernalized tillers. The upregulation of putative VRN1 or VRN2 genes was restricted to vernalized tillers in the spring yield and, thus, not detected in non-vernalized tillers of the second yield; so-called regrowth.
The formation of a lignified sclerenchyma ring that efficiently reduces the digestibility of the stem was not related to apex development but rather to a requirement for mechanical support. The observed good freezing tolerance of reproductive timothy tillers could be one important adaptation mechanism ensuring high yields in northern conditions. Both VRN1 and VRN2 homologues required a vernalization signal for expression so the development of yield-forming tillers in regrowth was regulated independently of the studied genes.
梯牧草是一种长日照草种，非常适合在高纬度地区种植。它不仅在春季生长，而且在夏季后期也会产生伸长的分蘖。由于收获生物量的数量和质量取决于冠层结构和形成茎的开花分蘖的比例，因此，开花的调控在饲料草生产中非常重要。
在温室和田间试验中研究了春化梯牧草的冠层结构、茎形态和抗寒性。通过分析梯牧草 apex 发育与花诱导因子 VRN1 和抑制因子 VRN2 同源物表达之间的关系，研究了发育的分子控制。
无论 apex 的发育阶段如何，春化和再生长的茎中都有真正的茎形成和木质素化的韧皮部环。然而，茎的形态有分歧。春化促进开花，当 apex 进入生殖阶段时，VRN1 同源物的表达升高。高 VRN1 同源物表达与抗寒性降低无关，并且与花抑制因子 VRN2 同源物的表达水平升高相关。田间试验支持观察到的春化分蘖中 VRN1 同源物的上调与向生殖阶段的转变之间的联系。VRN1 或 VRN2 同源物的上调仅限于春季产量的春化分蘖，因此在第二个产量即所谓的再生长的非春化分蘖中检测不到；因此，在非春化分蘖中检测不到。
木质素化韧皮部环的形成，有效地降低了茎的消化率，与 apex 发育无关，而是与机械支撑的要求有关。观察到生殖梯牧草分蘖具有良好的抗寒性，这可能是确保在北方条件下高产的一个重要适应机制。VRN1 和 VRN2 同源物的表达都需要春化信号，因此，再生长中产量形成分蘖的发育独立于所研究的基因进行调控。
