Shadow on the Plant: A Strategy to Exit.

The light spectrum perceived by plants is affected by crowding, which results in the shade avoidance syndrome (SAS). Findings presented by Pedmale et al. bring cryptochromes to the forefront of SAS and elucidate a fascinating molecular crosstalk between photoreceptor systems operating in different wavebands

The Arabidopsis plastid-signalling mutant gun1 (genomes uncoupled1) shows altered sensitivity to sucrose and abscisic acid and alterations in early seedling development

Developing seedlings of the Arabidopsis gun1 (genomes uncoupled1) mutant, which is defective in retrograde plastid-to-nucleus signalling, show several previously unrecognized mutant phenotypes. gun1 seedlings accumulated less anthocyanin than wild-type seedlings when grown in the presence of 2% (w/v) sucrose, due to lower amounts of transcripts of early anthocyanin biosynthesis genes in gun1. Norflurazon and lincomycin, which induce retrograde signalling, further decreased the anthocyanin content of sucrose-treated seedlings, and altered the temporal pattern of anthocyanin accumulation. Lincomycin treatment altered the spatial pattern of sucrose-induced anthocyanin accumulation, suggesting that plastids provide information for the regulation of anthocyanin biosynthesis in Arabidopsis seedlings. The temporal pattern of accumulation of LHCB1 transcripts differed between wild-type and gun1 seedlings, and gun1 seedlings were more sensitive to sucrose suppression of LHCB1 transcript accumulation than wild-type seedlings. Growth and development of gun1 seedlings was more sensitive to exogenous 2% sucrose than wild-type seedlings and, in the presence of lincomycin, cotyledon expansion was enhanced in gun1 seedlings compared to the wild type. gun1 seedlings were more sensitive than wild-type seedlings to the inhibition of seedling growth and development by abscisic acid. These observations clearly implicate GUN1 and plastid signalling in the regulation of seedling development and anthocyanin biosynthesis, and indicate a complex interplay between sucrose and plastid signalling pathways

Blue-Light-Induced Changes in Arabidopsis Cryptochrome 1 Probed by FTIR Difference Spectroscopy

Cryptochromes are blue-light photoreceptors that regulate a variety of responses in animals and plants, including circadian entrainment in Drosophila and photomorphogenesis in Arabidopsis. They comprise a photolyase homology region (PHR) of about 500 amino acids and a C-terminal extension of varying length. In the PHR domain, flavin adenine dinucleotide (FAD) is noncovalently bound. The presence of a second chromophore, such as methenyltetrahydrofolate, in animal and plant cryptochromes is still under debate. Arabidopsis cryptochrome 1 (CRY1) has been intensively studied with regard to function and interaction of the protein in vivo and in vitro. However, little is known about the pathway from light absorption to signal transduction on the molecular level. We investigated the full-length CRY1 protein by Fourier transform infrared (FTIR) and UV/vis difference spectroscopy. Starting from the fully oxidized state of the chromophore FAD, a neutral flavoprotein radical is formed upon illumination in the absence of any exogenous electron donor. A preliminary assignment of the chromophore bands is presented. The FTIR difference spectrum reveals only moderate changes in secondary structure of the apoprotein in response to the photoreduction of the chromophore. Deprotonation of an aspartic or glutamic acid, probably D396, accompanies radical formation, as is deduced from the negative band at 1734 cm(-)(1) in D(2)O. The main positive band at 1524 cm(-)(1) in the FTIR spectrum shows a strong shift to lower frequencies as compared to other flavoproteins. Together with the unusual blue-shift of the absorption in the visible range to 595 nm, this clearly distinguishes the radical form of CRY1 from those of structurally highly homologous DNA photolyases. As a consequence, the direct comparison of cryptochrome to photolyase in terms of photoreactivity and mechanism has to be made with caution

Fluorescence behaviour of 5,10-Methenyltetrahydrofolate, 10-Formyltetrahydrofolate, 10-Formyldihydrofolate and 10-Formylfolate in aqueous solution at pH 8

The fluorescence spectroscopic behaviour of (6R,S)-5,10-methenyltetrahydrofolate (MTHF), (6R,S)-10-formyltetrahydrofolate (10-HCO-H4folate), 10-formyldihydrofolate (10-HCO-H2folate), and 10-formylfolate (10-HCO-folate) in aqueous Tris-HCl buffer at pH 8 is studied. MTHF and 10-HCO-folate were commercially available. 10-HCO-H4folate was prepared from MTHF by hydrolysis at room temperature under anaerobic conditions. 10-HCO-H2folate was prepared by oxidation of 10-HCO-H4folate under aerobic conditions. Fluorescence quantum distributions at room temperature and fluorescence signal decays at room temperature and liquid nitrogen temperature were measured. The fluorescence lifetimes determined at room temperature (liquid nitrogen temperature) are 10 ps (2.9 ns) for MTHF, 38 ps (3.7 ns) for 10-HCO-H4folate, 80 ps (10.5 ns) for 10-HCO-H2folate, and 7.1 ns (20 ns) for 10-HCO-folate. The results are discussed in terms of dyadic (pterin-benzoyl-glutamate) photo-induced electron transfer and dyadic fluorescent dynamics. (C) 2009 Elsevier B.V. All rights reserved

Fluorescence behaviour of (6R,S)-5,10-Methenyltetrahydrofolate, (6R,S)-10-Formyltetrahydrofolate, 10-Formyldihydrofolate, and 10-Formylfolate

The fluorescence spectroscopic behaviour of (6R,S)-5,10-methenyltetrahydrofolate (MTHF), (6R,S)-10-formyltetrahydrofolate (10-HCO-H4folate), 10-formyldihydrofolate (10-HCO-H2folate), and 10-formylfolate (10-HCO-folate) in aqueous Tris-HCl buffer at pH 8 is studied. MTHF and 10-HCO-folate were commercially available. 10-HCO-H4folate was prepared from MTHF by hydrolysis at room temperature under anaerobic conditions. 10-HCO-H2folate was prepared by oxidation of 10-HCO-H4folate under aerobic conditions. Fluorescence quantum distributions at room temperature and fluorescence signal decays at room temperature and liquid nitrogen temperature were measured. The fluorescence lifetimes determined at room temperature (liquid nitrogen temperature) are 10 ps (2.9 ns) for MTHF, 38 ps (3.7 ns) for 10-HCO-H4folate, 80 ps (10.5 ns) for 10-HCO-H2folate, and 7.1 ns (20 ns) for 10-HCO-folate. The results are discussed in terms of dyadic (pterin-benzoyl-glutamate) photo-induced electron transfer and dyadic fluorescent dynamics. (C) 2009 Elsevier B.V. All rights reserved