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See detailAn anionic class III peroxidase from zucchini may regulate hypocotyl elongation through its auxin oxidase activity.
Cosio, Claudia; Vuillemin, Loic; De Meyer, Mireille et al

in Planta (2009)

The high number of peroxidase genes explains the description of numerous physiological functions and the fact that the in planta function of a single isoform has never been characterized yet. We analyzed ... [more ▼]

The high number of peroxidase genes explains the description of numerous physiological functions and the fact that the in planta function of a single isoform has never been characterized yet. We analyzed in transgenic Arabidopsis thaliana the localization of a zucchini isoperoxidase (APRX), previously purified thanks to its pectin binding ability. We confirmed that the protein is localized near the cell wall, mainly produced in the elongation area of the hypocotyls and respond to exogenous auxin. In addition, the ectopic overexpression of APRX induced changes in growth pattern and a significant reduction of endogenous indole-3-acetic acid (IAA) level. In agreement with these observations APRX showed an elevated in vitro auxin oxidase activity. We propose that APRX participates in the negative feedback regulation of auxin level and consequently terminates the hypocotyl elongation process. [less ▲]

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See detailAdventitious rooting and xylogenesis are enhanced by methyl jasmonate in tobacco thin cell layers
FATTORINI, Laura; FALASKA, Guiseppina; Kevers, Claire ULg et al

in Planta (2009), 231

Adventitious roots (ARs) are induced by auxins. Jasmonic acid (JA) and methyl jasmonate (MeJA) are also plant growth regulators with many effects on development, but their role on ARs needs investigation ... [more ▼]

Adventitious roots (ARs) are induced by auxins. Jasmonic acid (JA) and methyl jasmonate (MeJA) are also plant growth regulators with many effects on development, but their role on ARs needs investigation. To this aim, we analyzed AR formation in tobacco thin cell layers (TCLs) cultured with 0.01–10 μM MeJA, either under root-inductive conditions, i.e., on medium containing 10 μM indole-3-butyric acid (IBA) and 0.1 μM kinetin, or without hormones. The explants were excised from the cultivars Samsun, Xanthii and Petite Havana, and from genotypes with altered AR-forming ability in response to auxin, namely the non-rooting rac mutant and the over-rooting Agrobacterium rhizogenes rolB transgenic line. Results show that NtRNR1 (G1/S) and Ntcyc29 (G2/M) gene activity, cell proliferation and meristemoid formation were stimulated in hormone-cultured TCLs by submicromolar MeJA concentrations. The meristemoids developed either into ARs and xylogenic nodules, or into xylogenic nodules only (rac TCLs). MeJA-induced meristemoid over-production characterized rolB TCLs. No rooting or xylogenesis occurred under hormone-free conditions, independently of MeJA and genotype. Endogenous JA progressively (days 1–4) increased in hormone-cultured TCLs in the absence of MeJA. JA levels were enhanced by 0.1 μM MeJA, on both days 1 and 4. Endogenous IBA was the only auxin detected, both in the free form and as IBA-glucose. Free IBA increased up to day 2, remaining constant thereafter (day 4). Its level was enhanced by 0.1 μM MeJA only on day 1, while IBA conjugation was not affected by MeJA. Taken together, these results show that an interplay between jasmonates and auxins regulates AR formation and xylogenesis in tobacco TCLs. [less ▲]

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See detailThree-dimensional pore space quantification of apple tissue using X-ray computed microtomography.
Mendoza, Fernando; Verboven, Pieter; Mebatsion, Hibru K. et al

in Planta (2007), 226(3), 559-70

The microstructure and the connectivity of the pore space are important variables for better understanding of the complex gas transport phenomena that occur in plant tissues. In this study, we present an ... [more ▼]

The microstructure and the connectivity of the pore space are important variables for better understanding of the complex gas transport phenomena that occur in plant tissues. In this study, we present an experimental procedure for image acquisition and image processing to quantitatively characterize in 3D the pore space of apple tissues (Malus domestica Borkh.) for two cultivars (Jonagold and Braeburn) taken from the fleshy part of the cortex using X-ray computer microtomography. Preliminary sensitivity analyses were performed to determine the effect of the resolution and the volume size (REV, representative elementary volume analysis) on the computed porosity of apple samples. For comparison among cultivars, geometrical properties such as porosity, specific surface area, number of disconnected pore volumes and their distribution parameters were extracted and analyzed in triplicate based on the 3D skeletonization of the pore space (medial axis analysis). The results showed that microtomography provides a resolution at the micrometer level to quantitatively analyze and characterize the 3D topology of the pore space in apple tissue. The computed porosity was confirmed to be highly dependent of the resolution used, and the minimum REV of the cortical flesh of apple fruit was estimated to be 1.3 mm(3). Comparisons among the two cultivars using a resolution of 8.5 mum with a minimum REV cube showed that in spite of the complexity and variability of the pore space network observed in Jonagold and Braeburn apples, the extracted parameters from the medial axis were significantly different (P-value < 0.05). Medial axis parameters showed potential to differentiate the microstructure between the two evaluated apple cultivars. [less ▲]

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See detailCytokinin application to the shoot apical meristem of Sinapis alba enhances secondary plasmodesmata formation.
Ormenese, Sandra ULg; Bernier, Georges ULg; Périlleux, Claire ULg

in Planta (2006), 224(6), 1481-4

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is ... [more ▼]

A single application of cytokinin benzyladenine causes a threefold increase in the frequency of plasmodesmata in the vegetative shoot apical meristem (SAM) of Sinapis alba plants. This increase is observed 20 h after application within all cell layers (L1, L2, L3) as well as at the interfaces between these layers. Evidence is presented indicating that cytokinin promotes mainly the formation of new secondary plasmodesmata. A similar increase in the frequency of secondary plasmodesmata was observed in the Sinapis SAM during the floral transition induced by a single long day, suggesting that this effect of the long day is mediated by cytokinin. [less ▲]

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See detailIncreased levels of glycerol-3-phosphate lead to a stimulation of flux into triacylglycerol synthesis after supplying glycerol to developing seeds of Brassica napus L. in planta.
Vigeolas, Hélène ULg; Geigenberger, Peter

in Planta (2004), 219(5), 827-35

Glycerol-3-phosphate (glycerol-3P) is a primary substrate for triacylglycerol synthesis. In the present study, changes in the levels of glycerol-3P during rape (Brassica napus L.) seed development and the ... [more ▼]

Glycerol-3-phosphate (glycerol-3P) is a primary substrate for triacylglycerol synthesis. In the present study, changes in the levels of glycerol-3P during rape (Brassica napus L.) seed development and the influence of manipulating glycerol-3P levels on triacylglycerol synthesis were investigated. (i) Glycerol-3P levels were high in young seeds and decreased during seed development at 30 and 40 days after flowering (DAF), when lipid accumulation was maximal. (ii) To manipulate glycerol-3P levels in planta, various concentrations of glycerol were injected directly into 30-DAF seeds, which remained otherwise intact within their siliques and attached to the plant. Injection of 0-10 nmol glycerol led to a progressive increase in seed glycerol-3P levels within 28 h. (iii). Increased levels of glycerol-3P were accompanied by an increase in the flux of injected [14C]sucrose into total lipids and triacylglycerol, whereas fluxes to organic acids, amino acids, starch, protein and cell walls were not affected. (iv) When [14C]acetate was injected into seeds, label incorporation into total lipids and triacylglycerol increased progressively with increasing glycerol-3P levels. (v) There was a strong correlation between the level of glycerol-3P and the incorporation of injected [14C]acetate and [14C]sucrose into triacylglycerol. (v) The results provide evidence that the prevailing levels of glycerol-3P co-limit triacylglycerol synthesis in developing rape seeds. [less ▲]

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See detailThe shoot apical meristem of Sinapis alba L. expands its central symplasmic field during the floral transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Bernier, Georges ULg et al

in Planta (2002), 215(1), 67-78

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into ... [more ▼]

The shoot apical meristem (SAM) is functionally subdivided into zones with distinct tasks. During vegetative growth the peripheral zone of the meristem gives rise to leaf primordia that develop into dorsiventral leaves under the influence of signals from the central zone. During the floral transition the function of the SAM is altered and its peripheral zone starts to form floral structures in a specific pattern. This requires alterations in the signal networks that coordinate the activities of the peripheral and central zone of the SAM. These signal networks are partly housed in the symplasmic space of the SAM. Dye-coupling experiments demonstrate that in the superficial layer of the Sinapis alba meristem this space is radially subdivided. The cells of the central zone are coupled into a symplasmic field, which is shielded from the peripheral zone by the positional closing of plasmodesmata. In the vegetative meristems, most of these central symplasmic fields have a triangular geometry and are relatively small in size. Plants that are induced to flower by exposure to a single long day alter the geometry as well as the size of their central symplasmic field. After two subsequent days under short photoperiod the central symplasmic fields exhibit a circular form. Simultaneously. their size strongly increases both in an absolute sense and relative to the enlarging meristem. The geometric change in the fields is hypothesized to be due to recruitment of extra initial cells, required to support the increase in phyllotactic complexity. The proportional increase in field size is interpreted as an adjustment in the balance between the central and peripheral zone of the SAM, accompanying the shift from leaf production to flower formation. [less ▲]

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See detailThe Frequency of Plasmodesmata Increases Early in the Whole Shoot Apical Meristem of Sinapis Alba L. During Floral Transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Deltour, Roger ULg et al

in Planta (2000), 211(3), 370-5

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1 ... [more ▼]

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin. [less ▲]

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See detailInvolvement of indole-3-acetic acid in the circadian growth of the first internode of Arabidopsis
Jouve, Laurent; Gaspar, Thomas ULg; Kevers, Claire ULg et al

in Planta (1999), 209(1), 136-142

The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity ... [more ▼]

The extension rate of the first inflorescence node of Arabidopsis was measured during light/dark or continuous light exposure and was found to exhibit oscillations which showed a circadian rhythmicity. Decapitation induced a strong inhibition of stem extension. Subsequent application of IAA restored growth and the associated extension-rate oscillations. In addition, IAA treatments, after decapitation, re-established the circadian rhythmicity visible in the intact plants during free run. This indicates that the upper zone of the inflorescence has a major influence on the extension rate of floral stems and implies a role for auxin. Application of N-(1-naphthyl)phthalamic acid, an IAA transport inhibitor, to an intact floral stem inhibited growth and the rhythmicity in the extension rate oscillations, indicating that IAA polar transport may play a role in the dynamics of stem elongation. Furthermore, IAA-aspartate application, after decapitation, did not restore growth and rhythmicity. Nevertheless, biochemical analysis of IAA and IAA-aspartate demonstrated circadian fluctuations of the endogenous levels of both compounds. These observations suggest that IAA metabolism is an essential factor in the regulation of the circadian growth rhythm of Arabidopsis floral stems. [less ▲]

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See detailIsolation and characterization of photoactive complexes of NADPH : protochlorophyllide oxidoreductase from wheat
Chahdi, M. A. O.; Schoefs, B.; Franck, Fabrice ULg

in Planta (1998), 206(4), 673-680

A photoactive substrate-enzyme complex of the NADPH:protochlorophyllide oxidoreductase (POR; EC 1.3.1.33) was purified from etiolated Triticum aestivum L. by gel chromatography after solubilization of ... [more ▼]

A photoactive substrate-enzyme complex of the NADPH:protochlorophyllide oxidoreductase (POR; EC 1.3.1.33) was purified from etiolated Triticum aestivum L. by gel chromatography after solubilization of prolamellar bodies by dodecyl-maltoside. Irradiation by a 1-ms flash induced the phototransformation of protocholorophyllide a (Pchlide) with -196 degrees C absorbance and emission maxima at 640 and 643 nm, respectively. The apparent molecular weight of this complex was 112 +/- 24 kDa, which indicates aggregation of enzyme subunits. By lowering the detergent concentration in the elution buffer, a 1080 +/- 250-kDa particle was obtained which displayed the spectral properties of the predominant form of photoactive Pchlide in vivo (-196 degrees C absorbance and fluorescence maxima at 650 and 653 nm). In this complex, FOR was the dominant polypeptide. Gel chromatography in the same conditions of an irradiated sample of solubilized prolamellar bodies indicated rapid disaggregation of the complex after Pchlide phototransformation. High performance liquid chromatographic analysis of the FOR complexes obtained using two detergent concentrations indicates a possible association of zeaxanthin and violaxanthin with the photoactive complex. [less ▲]

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See detailChanges in gene expression in the leaf of Lolium temulentum L. Ceres during the photoperiodic induction of flowering
Périlleux, Claire ULg; Ongena, Philippe; Bernier, Georges ULg

in Planta (1996), 200(1), 32-40

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 µmol photons·m-2·s-1, fluorescence ... [more ▼]

Unifoliated plants of Lolium temulentum L. Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 µmol photons·m-2·s-1, fluorescence + incandescence) with incandescence at 10–15 µmol photonsm -2·s-1. The polyadenylated-RNA complement of leaf blade tissues was analysed at 4-h intervals during the photoperiod extension in LD vs. SD, by using two-dimensional polyacrylamide gel electrophoresis to resolve in-vitro-translated products. Of the 991 spots that were analysed, none appeared or disappeared during the inductive cycle, i.e. no qualitative effect of floral induction was detected, at any time. Sixty-eight spots were found whose intensity was influenced by lengthening of the photoperiod; 50 of them, i.e. ca. 5 of the population analysed, were affected before the end of the extension period and were thus potentially related to floral induction. Many of these RNAs were not quantitatively constant during a 24-h cycle in SD. Seven of them oscillated according to the ‘light-on’ and the ‘light-off’ signals, among which three seemed to be controlled by phytochrome since their relative amount increased under the standard light conditions but decreased under incandescence even faster than in darkness. The large majority of other RNAs varied with a timing that was not clearly driven by the alternation of light and darkness, indicating that genes related to the biological clock may be especially sensitive to the lengthening of the photoperiod. Furthermore, seven spots were observed that underwent a phase-shift in LD, which consisted, for six of them, of a phase advance of 4–8 h. The steady-state level of CAB mRNA was analysed because the CAB gene family (encoding the chlorophyll a/b-binding proteins of the light-harvesting complexes) is known to be controlled both by the biological clock and phytochrome. In SD, the level was high in the light and low in darkness; the fluctuation was conducted by a circadian rhythm. When plants were exposed to the inductive LD, the peak of mRNA accumulation that was expected according to the endogenous rhythmicity was abolished, possibly because of the change in light quality during the LD extension. [less ▲]

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See detailThe action of exogenous abscisic acid on malate synthase synthesis in germinating castor bean seeds
Dommes, Jacques ULg; Northcote, D. H.

in Planta (1985), 166

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