Journal Article

Vernalization response of <i>Phleum pratense</i> and its relationships to stem lignification and floral transition

Mervi M. Seppänen, Kirsi Pakarinen, Venla Jokela, Jeppe R. Andersen, Alice Fiil, Arja Santanen and Perttu Virkajärvi

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 106, issue 5, pages 697-707
Published in print November 2010 | ISSN: 0305-7364
Published online August 2010 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcq174
Vernalization response of Phleum pratense and its relationships to stem lignification and floral transition

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  • Ecology and Conservation
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  • Plant Sciences and Forestry

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Background

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.

Methods

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.

Key Results

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.

Conclusions

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.

Keywords: Apex development; canopy structure; elongation; flowering; freezing tolerance; lignification; Phleum pratense; regrowth; sclerenchyma ring; spring growth; timothy; vernalization; VRN1; VRN2

Journal Article.  6640 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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