Search

The methylation of daphnetin (7,8-dihydroxycoumarin) to its 8-methyl derivative is catalyzed by a wheat (Triticum aestivum L.) O-methyltransferase (TaOMT1). This enzyme is regulated by cold and photosystem II excitation pressure (plastid redox state). Here, we investigated the biological significance of this methylation and its potential role in modulating the activity of kinases in wheat. To identify the potential kinases that may interact with daphnetin in wheat, the soluble protein extract from aerial parts of cold-acclimated wheat was purified by DEAE-ellulose separation and affinity chromatography on a daphnetin derivative (7,8-dihydroxy-4-coumarin acetic acid)-EAH sepharose column. Mass spectrometric analysis indicated that wheat phosphoribulokinase (TaPRK) is the major kinase that binds to daphnetin. This TaPRK plays an important role in regulating the flow of carbon through the Calvin cycle, by catalyzing the final step in the regeneration of ribulose 1,5-bisphosphate from ribulose-5-phosphate (Ru5P) and ATP. The activities of TaPRK, endogenous or recombinant, are inhibited by daphnetin in a specific and dose-dependent manner, but not by its monomethyl derivative (7-methyl, 8-hydroxycoumarin). Furthermore, HPLC-MS analysis of wheat extracts reveals that 7,8-dimethoxycoumarin is more abundant than its monomethyl derivative. The results also show that cold acclimation does not alter the level of TaPRK mRNA or its enzyme activity, and thus ensures the stable generation of ribulose 1,5-biphosphate. Key words: phosphoribulokinase, O-Methylation, coumarin, cold acclimation, wheat. La methylation de la daphnetine (7,8-dihydroxycoumarin) et de son derive 8-methyle est catalysee par une O-methyltransferase du ble (Triticum aestivum L.) (TaOMT1). Cette enzyme est regulee par le froid et la pression d'excitation du photosysteme II (etat redox du plastide). Nous examinons ici la signification biologique de cette methylation et son role potentiel dans la modulation de l' activite des kinases du ble. Afin d' identifier les kinases qui peuvent possiblement interagir avec la daphetine du ble, un extrait proteique soluble des parties aeriennes de ble acclimate au froid a ete purifie par une separation sur DEAE-cellulose et une chromatographie d' affinite sur une colonne EAH-sepharose couplee a un derive de la daphnetine (acide 7,8 dihydroxy-4-coumarin acetique). Une analyse en spectrometrie de masse a indique que la phosphoribulokinase du ble (TaPRK) est la principale kinase qui lie la daphnetine. Cette TaPRK joue un role important en regulant le flux de carbone a travers le cycle de Calvin en catalysant l'etape finale de regeneration du ribulose 1,5-biphosphate a partir du ribulose 5-phosphate (Ru5P) et l'ATP. Les activites de la TaPRK, endogene ou recombinante, sont inhibees par la daphnetine de facon specifique et dependante de la concentration, mais pas par son derive mono-methyle (7-methyl, 8-hydroxycoumarin). De plus, l'analyse en HPLC-MS d'extraits de ble revele que le 7,8-dimethylhydroxycoumarin est plus abondant que son derive mono-methyle. Les resultats montrent aussi que l'acclimatation au froid ne modifie pas le niveau d'ARNm de TaPRK ni son activite enzymatique, faisant en sorte que la generation stable de ribulose 1,5-biphosphate est assuree. Mots-cles : phosphoribulokinase, O-methylation, coumarin, acclimatation au froid, ble. [Traduit par la Redaction], Introduction Low temperature (LT) is one of the most common environmental factors influencing growth, development, and survival of plants. Winter-hardy plants are able to tolerate extreme subzero temperatures. This tolerance [...]

We assessed the effects of short-term elevated C[O.sub.2] on the light-saturated rates of photosynthesis ([A.sub.sat]) of spring ('SR4A', 'Katepwa') and winter ('Musketeer', 'Norstar') wheat (Triticum aestivum L.) and rye (Secale cereale L.) cultivars grown at ambient C[O.sub.2] (380 µmol Cx[mol.sup.-1]) at either 20/16 °C (nonacclimated, NA) or 5/5 °C (cold acclimated, CA). In spring wheat-rye, cold acclimation decreased C[O.sub.2]-stimulation of [A.sub.sat] by 45%-60% relative to NA controls following a short-term (80 h) shift of plants from ambient to elevated C[O.sub.2] (700 µmol C*[mol.sup.-1]). In contrast, in winter wheat-rye, cold acclimation enhanced C[O.sub.2]stimulation of [A.sub.sat] by 15%-35% relative to NA controls upon a shift to elevated C[O.sub.2]. The stimulation observed for CA spring cultivars was about 60% less than that of CA winter cultivars. We conclude that a short-term exposure of spring cultivars to elevated C[O.sub.2] cannot compensate for the cold acclimation-induced inhibition of [A.sub.sat]. Cold acclimation of spring cultivars appeared to exacerbate Rubisco C[O.sub.2] substrate limitations present under ambient C[O.sub.2]. Furthermore, CA spring cultivars were unable to adjust their short-term temperature sensitivity of [A.sub.sat] under elevated C[O.sub.2] compared with the winter cultivars. Key words: cold acclimation, short-term elevated C[O.sub.2], light-saturated rates of photosynthesis, C[O.sub.2]stimulation, temperature sensitivity, winter and spring cereals. Les auteurs ont examine les effets d'une augmentation du C[O.sub.2] a court terme sur les taux de photosynthese saturee en lumiere ([A.sub.sat]) sur du ble (Triticum aestivum L.) de printemps ('SR4A', 'Katepwa')etd'hiver ('Musketeer', 'Norstar') ainsi que sur des cultivars de seigle (Secale cereale L.) cultives en presence de C[O.sub.2] ambiant (380 µmol C*[mol.sup.-1]) a 20/16 °C (non acclimate, NA) ou 5/5 °C (acclimate au froid, AF). Chez les bles et les seigles de printemps, l'acclimatation au froid diminue la stimulation du C[O.sub.2] en [A.sub.sat] de 45%-60%, comparativement aux temoins NA, a la suite d'un deplacement a court terme (80 h) des plantes du C[O.sub.2] ambiant a eleve (700 µmol C*[mol.sup.-1]). Au contraire, chez les bles et seigles d'hiver, l'acclimatation au froid augmente la stimulation du C[O.sub.2] en [A.sub.sat] de 15%-35% comparativement aux temoins NA suite a un retrait du C[O.sub.2] eleve. La stimulation observee chez les cultivars de printemps AF est d'environ 60% inferieure a celle des cultivars d' hiver AF. Les auteurs concluent que l' exposition a court terme des cultivars de printemps au C[O.sub.2] eleve ne peut pas compenser pour l'inhibition induite par l'acclimatation au froid en Asat.L'acclimatation au froid des cultivars de printemps semble exacerber les limitations de la Rubisco par le substrat C[O.sub.2], en presence du C[O.sub.2] ambiant. De plus, les cultivars de printemps ne peuvent ajuster leur sensibilite a la temperature a court terme de l'Asat en presence de C[O.sub.2] eleve, comparativement aux cultivars d' hiver. Mots-cles : acclimatation au froid, augmentation du C[O.sub.2] a court terme, taux de photosynthese en presence de lumiere saturante, stimulation par le C[O.sub.2], sensibilite a la temperature, cereales d'hiver et de printemps. [Traduit par la Redaction], Introduction Acclimation of the photosynthetic apparatus to low, nonfreezing temperatures has been extensively studied in both cold-sensitive and cold-tolerant species (Adams et al. 2002; Ensminger et al. 2006). It is [...]

Abstract: In plants and algal cells, changes in light intensity can induce intrachloroplastic and retrograde regulation of gene expression in response to changes in the plastoquinone redox status. We review [...]