title: Nocturnal changes in leaf growth of Populus deltoides are controlled by cytoplasmic growth.
abstract: Growing leaves do not expand at a constant rate but exhibit pronounced diel growth rhythms. However, the mechanisms giving rise to distinct diel growth dynamics in different species are still largely unknown. As a first step towards identifying genes controlling rate and timing of leaf growth, we analysed the transcriptomes of rapidly expanding and fully expanded leaves of Populus deltoides Bartr. ex. Marsh at points of high and low expansion at night. Tissues with well defined temporal growth rates were harvested using an online growth-monitoring system based on a digital image sequence processing method developed for quantitative mapping of dicot leaf growth. Unlike plants studied previously, leaf growth in P. deltoides was characterised by lack of a base-tip gradient across the lamina, and by maximal and minimal growth at dusk and dawn, respectively. Microarray analysis revealed that the nocturnal decline in growth coincided with a concerted down-regulation of ribosomal protein genes, indicating deceleration of cytoplasmic growth. In a subsequent time-course experiment, Northern blotting and real-time RT-PCR confirmed that the ribosomal protein gene RPL12 and a cell-cycle gene H2B were down-regulated after midnight following a decrease in cellular carbohydrate concentrations. Thus, we propose that the spatio-temporal growth pattern in leaves of P. deltoides primarily arises from cytoplasmic growth whose activity increases from afternoon to midnight and thereafter decreases in this species.
authors.affiliation: Institut for Chemistry and Dynamics of the Geosphere: Phytosphere (ICG-III), Research Centre Jülich, 52425 Jülich, Germany. s.matsubara@fz-juelich.de
authors.forename: Shizue
authors.initials: S
authors.lastname: Matsubara
authors.forename: Vaughan
authors.initials: V
authors.lastname: Hurry
authors.forename: Nathalie
authors.initials: N
authors.lastname: Druart
authors.forename: Catherine
authors.initials: C
authors.lastname: Benedict
authors.forename: Ingar
authors.initials: I
authors.lastname: Janzik
authors.forename: Andrés
authors.initials: A
authors.lastname: Chavarría-Krauser
authors.forename: Achim
authors.initials: A
authors.lastname: Walter
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schurr
mesh_terms: D050260:Carbohydrate Metabolism; D002940:Circadian Rhythm; D016000:Cluster Analysis; D003593:Cytoplasm / Q000502:physiology*; D003624:Darkness; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006657:Histones / Q000235:genetics / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D018515:Plant Leaves / Q000166:cytology / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D032107:Populus / Q000166:cytology / Q000254:growth & development*; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D006657:Histones; D010940:Plant Proteins; D012269:Ribosomal Proteins