Etiolated Seedlings (etiolated + seedling)

Distribution by Scientific Domains

Selected Abstracts

Phototropins and Their LOV Domains: Versatile Plant Blue-Light Receptors

Winslow R. Briggs
Abstract The phototropins phot1 and phot2 are plant blue-light receptors that mediate phototropism, chloroplast movements, stomatal opening, leaf expansion, the rapid inhibition of hypocotyl growth in etiolated seedlings, and possibly solar tracking by leaves in those species in which it occurs. The phototropins are plasma membrane-associated hydrophilic proteins with two chromophore domains (designated LOV1 and LOV2 for their resemblance to domains in other signaling proteins that detect light, oxygen, or voltage) in their N-terminal half and a classic serine/threonine kinase domain in their C-terminal half. Both chromophore domains bind flavin mononucleotide (FMN) and both undergo light-activated formation of a covalent bond between a nearby cysteine and the C(4a) carbon of the FMN to form the signaling state. LOV2-cysteinyl adduct formation leads to the release downstream of a tightly bound amphipathic ,-helix, a step required for activation of the kinase function. This cysteinyl adduct then slowly decays over a matter of seconds or minutes to return the photoreceptor chromophore modules to their ground state. Functional LOV2 is required for light-activated phosphorylation and for various blue-light responses mediated by the phototropins. The function of LOV1 is still unknown, although it may serve to modulate the signal generated by LOV2. The LOV domain is an ancient chromophore module found in a wide range of otherwise unrelated proteins in fungi and prokaryotes, the latter including cyanobacteria, eubacteria, and archaea. Further general reviews on the phototropins are those by Celaya and Liscum (2005) and Christie and Briggs (2005). [source]

Rice sucrose-phosphate synthase: Identification of an isoform specific for heterotrophic tissues with distinct metabolite regulation from the mature leaf enzyme

Gabriela C. Pagnussat
Immunohistological analyses for rice (Oryza sativa) sucrose-phosphate synthase (SPS, UDP-glucose d -fructose-6-phosphate-2-glucosyltransferase, EC show that the protein is differently localized in photosynthetic and etiolated leaves. Very little is known about SPS regulation in heterotrophic tissues; therefore, we studied the biochemical properties of the enzyme from etiolated seedlings and embryo. Two SPS forms (SPS-1 and SPS-2) were partially purified from etiolated seedlings. The effects of Glc-6-P (activator) and Pi (inhibitor) on SPS activities allowed us to differentiate the two forms. SPS-1 showed high sensitivity to Pi which also strongly decreased enzyme activation by Glc-6-P. SPS-2 was highly activated by Glc-6-P and showed low sensitivity to Pi. In vitro alkaline phosphatase treatment suggested that SPS-1 could be regulated as leaf SPS in darkness and that SPS-2 is present in a dephosphorylated state or is not regulated by protein phosphorylation. The relative MM value (116 kDa) estimated for both SPS forms in SDS-PAGE is identical to the rice leaf SPS polypeptide. Taken together, these data led us to conclude that SPS-2 is an enzyme form only present in non-photosynthetic tissues. [source]

Concurrent interactions of heme and FLU with Glu tRNA reductase (HEMA1), the target of metabolic feedback inhibition of tetrapyrrole biosynthesis, in dark- and light-grown Arabidopsis plants

David Goslings
Summary The regulation of tetrapyrrole biosynthesis in higher plants has been attributed to metabolic feedback inhibition of Glu tRNA reductase by heme. Recently, another negative regulator of tetrapyrrole biosynthesis has been discovered, the FLU protein. During an extensive second site screen of mutagenized flu seedlings a suppressor of flu, ulf3, was identified that is allelic to hy1 and encodes a heme oxygenase. Increased levels of heme in the hy1 mutant have been implicated with inhibiting Glu tRNA reductase and suppressing the synthesis of , -aminolevulinic acid (ALA) and Pchlide accumulation. When combined with hy1 or ulf3 upregulation of ALA synthesis and overaccumulation of protochlorophyllide in the flu mutants were severely suppressed supporting the notion that heme antagonizes the effect of the flu mutation by inhibiting Glu tRNA reductase independently of FLU. The coiled-coil domain at the C-terminal end of Glu tRNA reductase interacts with FLU, whereas the N-terminal site of Glu tRNA reductase that is necessary for the inhibition of the enzyme by heme is not required for this interaction. The interaction with FLU is specific for the Glu tRNA reductase encoded by HEMA1 that is expressed in photosynthetically active tissues. FLU seems to be part of a second regulatory circuit that controls chlorophyll biosynthesis by interacting directly with Glu tRNA reductase not only in etiolated seedlings but also in light-adapted green plants. [source]

A novel cold-inducible gene from Arabidopsis, RCI3, encodes a peroxidase that constitutes a component for stress tolerance

Francisco Llorente
Summary A cDNA from Arabidopsis corresponding to a new cold-inducible gene, RCI3 (for Rare Cold Inducible gene 3), was isolated. Isoelectric focusing electrophoresis and staining of peroxidase activity demonstrated that RCI3 encodes an active cationic peroxidase. RNA-blot analysis revealed that RCI3 expression in response to low temperature is negatively regulated by light, as RCI3 transcripts were exclusively detected in etiolated seedlings and roots of adult plants. RCI3 expression was also induced in etiolated seedlings, but not in roots, exposed to dehydration, salt stress or ABA, indicating that it is subjected to a complex regulation through different signaling pathways. Analysis of transgenic plants containing RCI3::GUS fusions established that this regulation occurs at the transcriptional level during plant development, and that cold-induced RCI3 expression in roots is mainly restricted to the endodermis. Plants overexpressing RCI3 showed an increase in dehydration and salt tolerance, while antisense suppression of RCI3 expression gave dehydration- and salt-sensitive phenotypes. These results indicate that RCI3 is involved in the tolerance to both stresses in Arabidopsis, and illustrate that manipulation of RCI3 has a potential with regard to plant improvement of stress tolerance. [source]