Effect of growth irradiance on plastocyanin levels in barley

Plastocyanin levels in barley (Hordeum vulgare cv Boone) were found to be dependent on growth irradiance. An immunochemical assay was developed and used to measure the plastocyanin content of isolated thylakoid membranes. Barley grown under 600 mole photons m^–2s^–1 contained two- to four-fold greater quantities of plastocyanin per unit chlorophyll compared with plants grown under 60 mole photons m^–2s^–1. The plastocyanin/Photosystem I ratio was found to be 2 to 3 under high irradiance compared with 0.5 to 1.5 under low irradiance. The reduced plastocyanin pool size in low light plants contributed to a two-fold reduction in photosynthetic electron transport activity. Plastocyanin levels increased upon transfer of low light plants to high irradiance conditions. In contrast, plastocyanin levels were not affected in plants transferred from high to low irradiance, suggesting that plastocyanin is not involved in the acclimation of photosynthesis to shade.Abbreviations: BSA bovine serum albumin - chl chlorophyll - cyt cytochrome - DCIP 2,6-dichlorophenolindophenol - PS I Photosystem I - PS II Photosystem II - P700 reaction center of Photosystem I - TBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl - TTBS 20 mM Tris-HCl pH 7.5, 500 mM NaCl, 0.5% (w/v) polyoxyethylenesorbitan monolaurate (Tween-20)     

The <Emphasis Type="Italic">Fed-1</Emphasis> (CAUU)<Subscript>4</Subscript> element is a 5′ UTR dark-responsive mRNA instability element that functions independently of dark-induced polyribosome dissociation

Darkness rapidly induces a decline in the stability and translation of the pea Ferredoxin-1 (Fed-1) mRNA in transgenic tobacco. Direct half-life measurement showed that mutation of the (CAUU)₄ stabilizes Fed-1 mRNA in the dark. (CAUU)₁, a feature more common in plant 5 UTRs than (CAUU)₄, confers slight light-responsive mRNA accumulation. At least three but less than 11 CAUU repeats near the 5 end of the 5 UTR are required for full light-responsive accumulation. Furthermore, 26nt of the 5 UTR, including the (CAUU)₄ repeat, is sufficient to confer a significant 2.5-fold increase in light-regulated mRNA accumulation when fused to the 5 end of a heterologous plant mRNA. A mutation of the (CAUU)₄ repeat that compromises light-regulated mRNA stability changes in vitro the accessibility of the region to ribonuclease V₁ and ribonuclease A suggesting the geometry formed by the repeat may be important for instability. Finally, dark-induced Fed-1 mRNA instability occurs even when most of the mRNA is retained on polyribosomes, and thus is likely an independent event regulated by darkness.     

Effect of 4-Thiouridine on Photosystems of a Higher Plant

Effect of 4-thiouridine, which was proved to inhibit selectively and “light-reversibly” the synthesis of chloroplast ribosomal RNAs in radish cotyledons, on the photo-induced development of photosystem I, II and a complete electron transport chain was investigated with plastids obtained from 4-thiouridine treated dark-grown radish cotyledons after various times of development in the light. It was demonstrated that the 4-thioridine treated chloroplasts showed a higher activity of photoreduction than the control untreated chloroplasts in every system on a chlorophyll basis during the development after 24 hr illumination. This specific activity decreased in both chloroplasts, as the chloroplasts matured with the time of illumination. The activity per g of fresh cotyledons treated with 4-thiouridine, especially in the early stage of development, was lower than that of ones untreated with the drug because total chlorophyll content was poor, but the activity of the former was enhanced with the increase of total chlorophyll content upon illumination while the activity of the latter decreased on 24 hr illumination. Moreover, Hill reaction measurements showed that 4-thiouridine treated chloroplasts were saturated at lower light intensity than untreated ones inspite of the same content of chlorophyll in both the chloroplasts: photoreduction of NADP⁺ was saturated at 3000 lux for the former and at 5000 lux for the latter. Based upon these results, specific development of the chloroplast is discussed.     

DCL is a plant-specific protein required for plastid ribosomal RNA processing and embryo development

The defective chloroplast and leaf-mutable (dcl-m) mutation of tomato blocks chloroplast differentiation in leaf mesophyll cells and a signaling system that appears to be required for morphogenesis of palisade cells during leaf growth. To dissect the function of DCL, mutants with stable dcl alleles (dcl-s) were generated and examined for their phenotype. DCL/dcl-s plant produce dcl-s/dcl-s seeds with embryos arrested at the globular stage of development. The levels of several chloroplast- and nuclear-encoded proteins are strongly reduced in dcl-m mutant leaf sectors without significant changes in their corresponding mRNAs. The 4.5S rRNA fails to be processed efficiently, however, suggesting that DCL has a direct or indirect function in rRNA processing or correct ribosome assembly. Accordingly, chloroplasts in dcl-m sectors are impaired in polysome assembly, which can explain the reduced accumulation of chloroplast-encoded proteins. These results suggest that DCL is required for chloroplast rRNA processing, and emphasize the importance of plastid function during embryogenesis.     

hGM－CSF基因及其调控研究进展

人粒细胞－巨噬细胞集落刺激因子基因表达受到转录调控与转录后调控。５＇非转录区的一些顺式调控成分,如ＣＡＴＴ（Ａ／Ｔ）重复序列,富含ＧＣ序列,ＣＫ－１、ＣＫ－２、ｋＢ特异序列与可诱导的ＣｓＡ敏感增强子成分等在转录水平上调控ｈＧＭ－ＣＳＦ的表达。３＇非翻译区有一６２ｂｐ富含ＡＵ序列,这与ｍＲＮＡ的稳定性相关,在翻译水平调控ｈＧＭ－ＣＳＦ的表达,细胞因子与一些刺激因子通过不同的机制作用于ｈＧＭ－ＣＳＦ基     

Amino-terminal and hydrophobic regions of the Chlamydomonas reinhardtii plastocyanin transit peptide are required for efficient protein accumulation in vivo

Nucleus-encoded chloroplast proteins of vascular plants are synthesized as precursors and targeted to the chloroplast by stroma-targeting domains in N-terminal transit peptides. Transit peptides in Chlamydomonas reinhardtii are considerably shorter than those in vascular plants, and their stroma-targeting domains have similarities to both mitochondrial and chloroplast targeting sequences. To examine Chlamydomonas transit peptide function in vivo, deletions were introduced into the transit peptide coding region of the petE gene, which encodes the thylakoid lumen protein plastocyanin (PC). The mutant petE genes were introduced into a plastocyanin-deficient Chlamydomonas strain, and transformants that accumulated petE mRNA were analyzed for PC accumulation. The most profound defects were observed with deletions at the N-terminus and those that extended into the hydrophobic region in the C-terminal half of the transit peptide. PC precursors were detected among pulse-labeled proteins in transformants with N-terminal deletions, suggesting that these precursors cannot be imported and are degraded in the cytosol. Intermediate PC species were observed in a transformant deleted for part of the hydrophobic region, suggesting that this protein is defective in lumen translocation and/or processing. Thus, despite its shorter length, the bipartite nature of the Chlamydomonas PC transit peptide appears similar to that of lumen-targeted proteins in vascular plants. Analysis of the synthesis, stability, and accumulation of PC species in transformants bearing deletions in the stroma-targeting domain suggests that specific regions probably have distinct roles in vivo. Abbreviations: cyt, cytochrome; ECL, enhanced chemiluminescence; LSU, large subunit; PC, plastocyanin; TP, transit peptide     

Synthesis and accumulation of pea plastocyanin in transgenic tobacco plants

The pea plastocyanin gene in a 3.5 kbp Eco RI fragment of pea nuclear DNA was introduced into tobacco by Agrobacterium-mediated transformation. Regenerated plants contained pea plastocyanin located within the chloroplast thylakoid membrane system. Analysis of seedlings from a self-pollinated transgenic plant containing a single copy of the pea plastocyanin gene indicated that seedlings homozygous for the pea gene contained almost twice as much pea plastocyanin as seedlings hemizygous for the pea gene. Homozygous seedlings contained approximately equal amounts of pea and tobacco plastocyanins. The amount of tobacco plastocyanin in leaves of transgenic plants was unaffected by the expression of the pea plastocyanin gene. The mRNA from the pea gene in tobacco was indistinguishable by northern blotting and S1 nuclease protection from the mRNA found in pea. In both pea and transgenic tobacco, expression of the pea plastocyanin gene was induced by light in leaves but was suppressed in roots. Pea plastocyanin free of contaminating tobacco plastocyanin was purified from transgenic tobacco plants and shown to be indistinguishable from natural pea plastocyanin by N-terminal protein sequencing and ¹H NMR spectroscopy.     

hGM－CSF基因及其调控研究进展

人粒细胞-巨噬细胞集落刺激因子(hGM-CSF)基因表达受到转录调控与转录后调控.5＇非转录区的一些顺式调控成分,如CATT(A/T)重复序列,富含GC序列,CK-1、CK-2、kB特异序列与可诱导的CsA敏感增强子成分等在转录水平上调控hGM-CSF的表达.3＇非翻译区有一62bp富含AU序列,它与mRNA的稳定性相关,在翻译水平调控hGM-CSF的表达.细胞因子与一些刺激因子通过不同的机制作用于hGM-CSF基因,从而影响hGM-CSF的产生与分泌.