Metabolite Signature during Short-Day Induced Growth Cessation in Populus

Atsushi Fukushima,Johan Trygg,Jonas Gullberg,Michael Sjöström,Miyako Kusano,Pär Jonsson,Thomas Moritz

doi:10.3389/fpls.2011.00029

Abstract

The photoperiod is an important environmental signal for plants, and influences a wide range of physiological processes. For woody species in northern latitudes, cessation of growth is induced by short photoperiods. In many plant species, short photoperiods stop elongational growth after a few weeks. It is known that plant daylength detection is mediated by Phytochrome A (PHYA) in the woody hybrid aspen species. However, the mechanism of dormancy involving primary metabolism remains unclear. We studied changes in metabolite profiles in hybrid aspen leaves (young, middle, and mature leaves) during short-day-induced growth cessation, using a combination of gas chromatography–time-of-flight mass spectrometry, and multivariate projection methods. Our results indicate that the metabolite profiles in mature source leaves rapidly change when the photoperiod changes. In contrast, the differences in young sink leaves grown under long and short-day conditions are less distinct. We found short daylength induced growth cessation in aspen was associated with rapid changes in the distribution and levels of diverse primary metabolites. In addition, we conducted metabolite profiling of leaves of PHYA overexpressor (PHYAOX) and those of the control to find the discriminative metabolites between PHYAOX and the control under the short-day conditions. The metabolite changes observed in PHYAOX leaves, together with those in the source leaves, identified possible candidates for the metabolite signature (e.g., 2-oxo-glutarate, spermidine, putrescine, 4-amino-butyrate, and tryptophan) during short-day-induced growth cessation in aspen leaves.

Highlights

The initiation of cold acclimation and dormancy for tree species in northern latitudes is synchronized with the end of the growth season and the onset of low temperatures in the autumn
Design and experimental set-up for sampling We investigated which positions on hybrid aspen trees were representative of young, middle, and mature leaves for this study, to obtain insights into the extent of differences of metabolite composition of leaf samples across different developmental stages (Figure 1A)
The orthogonal projection to latent structures (OPLS) analysis, which is one of the supervised methods, clearly showed that metabolite profiles of aspen leaves were well correlated with their leaf positions (Figures 1A,C)

Summary

Introduction

The initiation of cold acclimation and dormancy for tree species in northern latitudes is synchronized with the end of the growth season and the onset of low temperatures in the autumn. In Populus, the site of daylength detection and cessation of stem elongation is in the leaf-rib meristem area (Ruonala et al, 2008). One of the main players in the signaling pathways involved in short-day-induced growth cessation is the flowering locus T (FT) protein. Transgenic poplars overexpressing the Populus FT-gene under the cauliflower mosaic virus 35S-promotor do not form buds during short photoperiods (Bohlenius et al, 2006). This suggests that the FT protein is a key mobile regulator of daylength-controlled shoot elongation in Populus, similar to the FT protein role in flowering in Arabidopsis (Corbesier et al, 2007) and rice (Tamaki et al, 2007)

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