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Nocturnal changes in leaf growth of Populus deltoides are controlled by cytoplasmic growth
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
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2006 (English)In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 223, no 6, 1315-1328 p.Article in journal (Refereed) Published
Abstract [en]

Growing leaves do not expand at a constantrate but exhibit pronounced diel growth rhythms.However, the mechanisms giving rise to distinct dielgrowth dynamics in different species are still largelyunknown. As a first step towards identifying genescontrolling rate and timing of leaf growth, we analysedthe transcriptomes of rapidly expanding and fully expandedleaves of Populus deltoides Bartr. ex. Marsh atpoints of high and low expansion at night. Tissues withwell defined temporal growth rates were harvested usingan online growth-monitoring system based on a digitalimage sequence processing method developed forquantitative mapping of dicot leaf growth. Unlike plantsstudied previously, leaf growth in P. deltoides wascharacterised by lack of a base-tip gradient across thelamina, and by maximal and minimal growth at duskand dawn, respectively. Microarray analysis revealedthat the nocturnal decline in growth coincided with aconcerted down-regulation of ribosomal protein genes,indicating deceleration of cytoplasmic growth. In asubsequent time-course experiment, Northern blottingand real-time RT-PCR confirmed that the ribosomalprotein gene RPL12 and a cell-cycle gene H2B weredown-regulated after midnight following a decrease incellular carbohydrate concentrations. Thus, we proposethat the spatio-temporal growth pattern in leaves ofP. deltoides primarily arises from cytoplasmic growthwhose activity increases from afternoon to midnight andthereafter decreases in this species.

Place, publisher, year, edition, pages
Berlin: Springer-Verlag , 2006. Vol. 223, no 6, 1315-1328 p.
Keyword [en]
Cell cycle, cytoplasmic growth, leaf growth, microarray, populus, ribosomal protein
URN: urn:nbn:se:umu:diva-5383DOI: 10.1007/s00425-005-0181-0OAI: diva2:144882
Available from: 2006-10-05 Created: 2006-10-05 Last updated: 2015-03-18Bibliographically approved
In thesis
1. Cold Acclimation: Dissecting the plant low temperature signaling pathway using functional genomics
Open this publication in new window or tab >>Cold Acclimation: Dissecting the plant low temperature signaling pathway using functional genomics
2006 (Swedish)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The physiological process of cold acclimation protects plants native to the temperate regions of the world from the deleterious effects of low and freezing temperatures. This is achieved by a series of transcriptional, regulatory, and metabolic changes that enable continued growth and survival. Within minutes of exposure to temperatures below ca. 10°C, a complex cascade of transcriptional events is initiated to accomplish these changes. The initial alarm phase favors the rapid induction of a library of stress proteins with protective functions (e.g. COR proteins). This is followed by a cold hardened phase, characterized by maximal freezing tolerance, which continues until either the stress is removed, or the plant's metabolic and/or developmental state can no longer support maximal resistance.

We have studied some of the important transcription factors and transcriptional changes associated with the initial alarm and later hardened phases of cold acclimation in the herbaceous annual Arabidopsis thaliana and the woody perennial Populus spp. We confirmed the functionality of the CBF-mediated signaling cascade in Poplar overexpressing AtCBF1, but noted that regulon composition and endogenous poplar CBF ortholog induction appeared to be tissue-specific. The lack of statistically significant DRE enrichment in the Poplar AtCBF1 regulons led us to investige cis-element abundance in the cold-associated transcription factor regulons of publicly available microarray data from Arabidopsis, leading to the development of a gene voting method of microarray analysis that we used to test for regulatory associations between transcription factors and their downstream cis-elements and gene targets. This analysis resulted in a new transcriptional model of the ICE1-mediated signaling cascade and implicated a role for phytochrome A. Application of this same method to microarray data from arabidopsis leaves developed at low temperature allowed us to identify a new cis-element, called DDT, which possessed enhancer-blocking function during the alarm stage of cold stress, but was enriched in the promoters of genes upregulated during the later cold hardened stages. As leaf growth and development at low temperature correlated with the enhancement freeze tolerance in Arabidopsis, we compared the transcriptomes of rapidly growing and fully grown poplar leaves at night (when both low temperatures and PhyA status might play important roles in nature), in the hopes of comparing this data with that of cold-treated leaves in the future. We identified the nocturnal mode of leaf growth in Populus deltoides as predominantly proliferative as opposed to expansive, and potentially linked to cellular carbohydrate status.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik, 2006. 51 p.
cold acclimation, functional genomics, microarray, Populus tremula, Arabidopsis thaliana, gene voting, regulon, enhancer-blocking
National Category
urn:nbn:se:umu:diva-885 (URN)91-7264-188-6 (ISBN)
Public defence
2006-10-27, KB3B1, KBC, KBC, Umeå, 10:00 (English)
Available from: 2006-10-05 Created: 2006-10-05 Last updated: 2011-03-30Bibliographically approved

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