Ethylene Inhibits Root Growth

Exogenous ethylene inhibits root elongation in different plant species. This was shown for Arabidopsis (reviewed by Bleecker et al. 1988 Smalle et al. 1997), cucumber (Pierik et al. 1999), and Rumex (Visser et al. 1997). This inhibition of elongation is at least partially dependent on an ethylene-induced inhibition of cell elongation. In Arabidopsis, wild-type epidermal cells with a visible root hair bulge (the first sign of root hair outgrowth) are shorter when treated with ACC or ethylene (Le...

Multiple Fission A Variation on the Theme

The cells of Chlamydomonas reinhardtii and Scenedesmus quadricauda divide by a variant of the common cell cycle, multiple fission. C. reinhardtii, S. quadricauda, and their relatives grown in light undergo a prolonged G1 phase during which they may grow to many (2n) times their original size. The n is determined by a combination of the growth rate and the species limitations (in most algae n can range from 3 to 5 in some species it can reach 10). With each doubling of size cells attain a...

Protein Interaction Networks

Inferring signalling networks solely from transcriptomics data has several limitations. For example, the discrete nature of the data could limit the complexity of the networks that can be inferred. Moreover, transcriptomics data can provide only a limited picture of the actual physiological changes underlying a living organism. This has been clearly shown very recently, through proteomic analysis of Arabidopsis suffering biotic stress. Jones et al. (2006) have analyzed the alterations in the...

Control of the Endocycle by Cell Cycle Related Genes

Dwarf Mutant Arabidopsis

Endoreduplication is often viewed as a short-cut of the mitotic cell cycle that skips mitosis and re-enters the S-phase. During the normal mitotic cell cycle, cells have a mechanism to prevent entry into the S-phase without going through the M-phase. Cells that initiate the endocycle, however, are able to break this rule and re-enter the S phase in the absence of mitosis (Fig. 3). Despite these key differences between the mitotic cell cycle and endocycle, at least some of the molecular...

An Unknown Long Distance Signaling Mechanism Governs Differentiation Into Sun or Shade Leaves

Leaf Cell Acclimation Light

We will now introduce recent studies that indicate the parts of the plant that recognize light and control the differentiation of new leaves, and discuss candidates for light recognition. Lake et al. 2001 showed that the stomatal index of developing Arabidopsis leaves decreased when mature leaves were shaded. The authors also showed that the stomatal density and index decreased when mature leaves were exposed to CO2-enriched air, and vice versa. These results indicate that stomatal development...

Characteristic Diel Cycles of Leaf Growth Activity

Leaves of all investigated species show characteristic diel cycles of growth activity under all reported environmental conditions for a review see Walter and Schurr 2005 or Matsubara and Walter 2006 . The intensity and the finestructure of the diel variation varies from day to day and the phasing clearly differs between species Fig. 3 Leaves of Ricinus communis Walter et al. 2002a , Nicotiana tabacum Walter and Schurr 2005 and Arabidopsis thaliana Wiese et al. 2007 for example showed maximal...

Promoting Factors

A multitude of Arabidopsis mutants show dwarfism because of reduced cell numbers and or cell size e.g., Autran et al. 2002 Nelissen et al. 2003 . However, for many of them overexpression of the respective gene where tested does not lead to extra growth, making it difficult to assess whether these genes fulfill a regulatory role. They will therefore not be discussed further here. Similarly, while activity of the core cell cycle machinery is obviously required for growth by proliferation,...

Interaction Partners to Short Modified Motifs

One of the main interests in signaling biology is to gain insight into how cells process information. In many signaling pathways, signaling molecules bind to receptor proteins and this information is passed on to ultimately induce tran-scriptional changes, often involving a series of protein phosphorylation events. A significant subset of these signal-dependent phosphorylation events creates new protein-protein interaction interfaces, which serve to recruit adaptor or effector molecules....

Regulation of Transcription by PP2C

Tobacco DNA-binding protein phosphatase DBP1 was isolated by interaction with the promoter region of tomato citrus exocortis viroid CEVI1 gene, which is induced during the course of compatible plant-virus interactions. The C-terminal part of DBP1 shows homology to the PP2C catalytic domain, whereas the N-terminal region contains DNA binding sequences Carrasco et al. 2003 . Correspondingly, DBP1 shows Mg2 -dependent phosphatase activity and contains a functional nuclear localization signal. DBP1...

Scenedesmus quadricauda

Scenedesmus is a genus of common nonmotile chlorophyte green freshwater alga that has been used for decades as a model organism for the regulation of the cell cycle, photosynthesis, and a variety of toxicity studies. The daughter cells coming from a division of a single mother cell stay connected by a common cell wall in structured clusters called coenobia in S. quadricauda coenobia could be either four- or eight-celled with the terminal cells having two spines. Individual cells contain a...