Patterns of Development and Nitrogen Reserves Mobilization during Regrowth of Defoliated Clover

Contribution of nitrogen reserves to regrowth following defoliation was studied in white clover plants (Trifolium repens) according to the morphological pattern of differentiation of the aerial parts during the same period. Low temperature and short day lengths were used as a pre-treatment in order to increase branching and enhance new sites of leaf production during a further 25 d period of regrowth. Pre-treated plants exhibited a large reduction in leaf area largely counterbalanced with a high increase in leaf pool size during the first 10 d of regrowth. The mobilization of nitrogen reserves during regrowth of defoliated clover was intimately linked to the pattern of differentiation of the newly developed organs. It thus appeared that regrowth of pretreated plants was less supported by endogenous N during the first 10 d as compared to control plants continously grown in standard conditions. It is assumed that regrowth of dwarf plants is less dependent upon the mobilization rate of soluble proteins previously accumulated in roots and uncut stolons

Modelling Nitrogen Uptake in Winter Oilseed Rape by Using Influx Kinetics of Nitrate Transport Systems

A mechanistic model was proposed in order to predict nitrogen uptake by a culture of oilseed rape (Brassica napus L.), using independently measured characteristics of plants growing in hydroponic or under field conditions. Uptake kinetics of the different components (Constitutive and Inducible) of the Low and High Affinity Transport Systems of nitrate (CLATS, ILATS, CHATS and IHATS, respectively) were determined by 15NO3- labelling in controlled conditions. The use of kinetic equations of transport systems and the experimental field data from the INRA-Châlons rape databank allowed to model NO3- uptake during the plant growth cycle. The study of different factors such as root temperature, day/night cycle and ontogenetic stages on NO3- uptake rate has been undertaken in order to improve the model prediction. Model outputs show that the high affinity transport system (HATS) accounted for about 90 % of total NO3- uptake (20 and 70 % for CHATS and IHATS without fertilization, respectively). The low affinity transport system (LATS) accounted for a minor proportion of total N uptake, and its activity was restricted to the early phase of the growth cycle. However, N autumnal fertilization increased the duration of its contribution (from 67 to 100 days) to total N uptake

Instantons revisited: dynamical tunnelling and resonant tunnelling

Starting from trace formulae for the tunnelling splittings (or decay rates) analytically continued in the complex time domain, we obtain explicit semiclassical expansions in terms of complex trajectories that are selected with appropriate complex-time paths. We show how this instanton-like approach, which takes advantage of an incomplete Wick rotation, accurately reproduces tunnelling effects not only in the usual double-well potential but also in situations where a pure Wick rotation is insufficient, for instance dynamical tunnelling or resonant tunnelling. Even though only one-dimensional autonomous Hamiltonian systems are quantitatively studied, we discuss the relevance of our method for multidimensional and/or chaotic tunnelling

A primer for resonant tunnelling

Resonant tunnelling is studied numerically and analytically with the help of a three-well quantum one-dimensional time-independent model. The simplest cases are considered where the three-well potential is polynomial or piecewise constant.Comment: accepted to EJP, 19 pages, 8 figure

Tunneling dynamics in exactly-solvable models with triple-well potentials

Inspired by new trends in atomtronics, cold atoms devices and Bose-Einstein condensate dynamics, we apply a general technique of N=4 extended Supersymmetric Quantum Mechanics to isospectral Hamiltonians with triple-well potentials, i.e. symmetric and asymmetric. Expressions of quantum-mechanical propagators, which take into account all states of the spectrum, are obtained, within the N = 4 SQM approach, in the closed form. For the initial Hamiltonian of a harmonic oscillator, we obtain the explicit expressions of potentials, wavefunctions and propagators. The obtained results are applied to tunneling dynamics of localized states in triple-well potentials and for studying its features. In particular, we observe a Josephson-type tunneling transition of a wave packet, the effect of its partial trapping and a non-monotonic dependence of tunneling dynamics on the shape of a three-well potential. We investigate, among others, the possibility of controlling tunneling transport by changing parameters of the central well, and we briefly discuss potential applications of this aspect to atomtronic devices.Comment: Latex, 28 pages, 7 Figs, 2 Tables; minor presentation changes, journal versio

Non-specificity of ethylene inhibitors: ‘double-edged’ tools to find out new targets involved in the root morphogenetic programme

International audienceIn the last decade, genetic and pharmacological approaches have been used to explore ethylene biosynthesis and perception in order to study the role of ethylene and ethylene/auxin interaction in root architecture development. However, recent findings with pharmacological approaches highlight the non-specificity of commonly used inhibitors. This suggests that caution is required for interpreting these studies and that the use of pharmacological agents is a ‘double-edged’ tool. On one hand, non-specific effects make interpretation difficult unless other experiments, such as with different mutants or with multiple diversely acting chemicals, are conducted. On the other hand, the non-specificity of inhibitors opens up the possibility of uncovering some ligands or modulators of new receptors such as plant glutamate-like receptors and importance of some metabolic hubs in carbon and nitrogen metabolism such as the pyridoxal phosphate biosynthesis involved in the regulation of the root morphogenetic programme. Identification of such targets is a critical issue to improve the efficiency of absorption of macronutrients in relation to root the morphogenetic programme

Nitrogen storage and remobilization in Brassica napus L. during the growth cycle: effects of methyl jasmonate on nitrate uptake, senescence, growth, and VSP accumulation

The role of methyl jasmonate (MeJa) in promoting senescence has been described previously in many species, but it has been questioned in monocarpic species whether induced senescence is a result of a potential death hormone like MeJa, or a consequence of an increased metabolic drain resulting from the growth of reproductive tissue. In oilseed rape (Brassica napus L.), a polypeptide of 23 kDa has been recently identified as a putative vegetative storage protein (VSP). This polypeptide could be used as a storage buffer between N losses from senescing leaves putatively promoted by methyl jasmonate that might be produced by flowers, and grain filling which occurs later on, while N uptake is strongly reduced. In order to describe causal relationships during Brassica napus L. plant responses to MeJa treatment, a kinetic experiment was performed to determine the order and the amplitude with which general processes such as growth, photosynthesis, chlorophyll content, N uptake, and N storage under the form of the 23 kDa VSP are affected. One of the most immediate consequences of MeJa treatment was the strong reduction of nitrate uptake within 6 h, relative to control plants. However, this was not a specific effect as K+ uptake was similarly affected. Photosynthesis was reduced later (after 24 h), while chlorophyll content as well as leaf growth also decreased in a similar way. Moreover, this was concomitant with a remobilization of endogenous unlabelled N from senescing leaves to roots. Accumulation of the 23 kDa VSP was induced in the taproot after 24 h of MeJa treatment and was increased 10-fold within 8 d. On the other hand, the reversible effect of a MeJa pretreatment was tested in the long term (i.e. along the growth cycle) using plants previously grown in field conditions induced for flowering. Results show that a MeJa pulse induced a reversible effect on N uptake inhibition. In parallel, protein immunologically related to the 23 kDa VSP was detected in stems with a similar molecular weight (23 kDa), and in flowers and leaves with a molecular weight of 24 kDa. This accumulation was concomitant with the remobilization of both subunits of Rubisco. During stem and pod development, this protein induced by MeJa is fully hydrolysed. The external and intermittent supply of MeJa mimic some of the plant physiological processes previously reported under natural conditions. This suggests that in oilseed rape, methyl jasmonate could be considered as a possible monocarpic senescence factor while accumulation/mobilization of the 23 kDa VSP in taproot could be a marker for the cessation of N uptake and the initiation of a massive leaf senescence

Effects of nitrate pulses on BnNRT1 and BnNRT2 genes: mRNA levels and nitrate influx rates in relation to the duration of N deprivation in Brassica napus L.

International audienc

Putative role of γ -aminobutyric acid (GABA) as a long-distance signal in up-regulation of nitrate uptake in Brassica napus L.

The relationship between nitrate influx, BnNrt2 nitrate transporter gene expression and amino acid composition of phloem exudate was investigated during N-deprivation (short-term experiment) and over a growth cycle (long-term experiment) in Brassica napus L. The data showed a positive correlation between γ-aminobutyric acid (GABA) in phloem exudate and nitrate uptake in the short- and the long-term experiments. The hypothesis that this non-protein amino acid could up-regulate nitrate uptake via a long-distance signalling pathway was tested by providing an exogenous GABA supply to the roots. The effect of GABA was compared with the effects of Gln, Glu and Asn, each known to be inhibitors of nitrate uptake. The results showed that GABA treatment induced a significant increase of BnNrt2 mRNA expression, but had less effect on nitrate influx. By contrast, Gln, Glu and Asn significantly reduced nitrate influx and BnNrt2 mRNA expression compared with the control plants. This study provides the first evidence that GABA may act as a putative long-distance inter-organ signal molecule in plants in conjunction with negative control exerted by Gln. The up-regulation effect of GABA on nitrate uptake is discussed in the context of its role in N metabolism, nutritional stress and the recent discovery of a putative role of GABA as a signal molecule in plant development.Peer reviewe