Modeling the pre- and post-synaptic components involved in the synaptic modification between cones and horizontal cells in carp retina

In retinal synapses between cones and luminosity type horizontal cells (LHC), it was previously found in this laboratory that repetitive red flashes progressively strengthened the LHC’s response to red flash, whereas weakened the LHC’s response to green flash; repetitive green flash remarkably depressed the LHC’s red response, but caused little changes in the cell’s green response. However, the detailed mechanisms underlying these phenomena are not entirely clear. In the present study, based on an ion-channel model described mainly in the form of Hodgkin–Huxley equations, possible mechanisms of the short-term synaptic modification are investigated. The simulation results suggest that: (1) the auto-enhancement effect might be induced by the Ca²⁺-dependent process on the post-synaptic AMPA receptors, which could lead to changes of the ionic channel’s properties; (2) the asymmetric response to red- and green-flashes and the mutual-chromatic suppression effects might be attributed to the regulatory effects on the presynaptic glutamate release.     

The fucoxanthin-chlorophyll proteins from a chromophyte alga are part of a large multigene family: structural and evolutionary relationships to other light harvesting antennae

 A fucoxanthin-chlorophyll protein (FCP) cDNA from the raphidophyte Heterosigma carterae encodes a 210-amino acid polypeptide that has similarity to other FCPs and to the chlorophyll a/b-binding proteins (CABs) of terrestrial plants and green algae. The putative transit sequence has characteristics that resemble a signal sequence. The Heterosigma fcp genes are part of a large multigene family which includes members encoding at least two significantly different polypeptides (Fcp1, Fcp2). Comparison of the FCP sequences to the recently determined three-dimensional structure of the pea LHC II complex indicates that many of the key amino acids thought to participate in the binding of chlorophyll and the formation of complex-stabilizing ionic interactions are well conserved. Phylogenetic analyses of sequences of light-harvesting proteins shows that the FCPs of several chromophyte phyla form a natural group separate from the intrinisic peridinin-chlorophyll proteins (iPCPs) of the dinoflagellates. Although the FCP and CAB genes shared a common ancestor, these lineages diverged from each other prior to the separation of the CAB LHC I and LHC II sequences in the green algae and terrestrial plants. Received: 8 July 1996 / Accepted: 21 August 1996     

Beyond spike timing: the role of nonlinear plasticity and unreliable synapses

 Spike-timing-dependent plasticity (STDP) strengthens synapses that are activated immediately before a postsynaptic spike, and weakens those that are activated after a spike. To prevent an uncontrolled growth of the synaptic strengths, weakening must dominate strengthening for uncorrelated spike times. However, this weight-normalization property would preclude Hebbian potentiation when the pre- and postsynaptic neurons are strongly active without specific spike-time correlations. We show that nonlinear STDP as inherent in the data of Markram et al. [(1997) Science 275:213–215] can preserve the benefits of both weight normalization and Hebbian plasticity, and hence can account for learning based on spike-time correlations and on mean firing rates. As examples we consider the moving-threshold property of the Bienenstock–Cooper–Munro rule, the development of direction-selective simple cells by changing short-term synaptic depression, and the joint adaptation of axonal and dendritic delays. Without threshold nonlinearity at low frequencies, the development of direction selectivity does not stabilize in a natural stimulation environment. Without synaptic unreliability there is no causal development of axonal and dendritic delays. Received: 22 April 2002 / Accepted: 23 May 2002 Acknowledgements. This study was supported by the Swiss National Science Foundation (grant 3152-065234.01) and the Silva-Casa foundation. The author thanks Stefano Fusi, Henry Markram, and Misha Tsodyks for helpful discussions, Nissim Buchs and Martin Schneider for their simulations, and Jan Reutimann for proof reading. Correspondence to: e-mail: wsenn@cns.unibe.ch, Tel.: +41-31-6318721, Fax: 41-31-6314611     

A Phylogenetic Assessment of the Eukaryotic Light-Harvesting Antenna Proteins, with Implications for Plastid Evolution

The light-harvesting complexes (LHCs) are a superfamily of chlorophyll-binding proteins present in all photosynthetic eukaryotes. The Lhc genes are nuclear-encoded, yet the pigment–protein complexes are localized to the thylakoid membrane and provide a marker to follow the evolutionary paths of plastids with different pigmentation. The LHCs are divided into the chlorophyll a/b-binding proteins of the green algae, euglenoids, and higher plants and the chlorophyll a/c-binding proteins of various algal taxa. This work examines the phylogenetic position of the LHCs from three additional taxa: the rhodophytes, the cryptophytes, and the chlorarachniophytes. Phylogenetic analysis of the LHC sequences provides strong statistical support for the clustering of the rhodophyte and cryptomonad LHC sequences within the chlorophyll a/c-binding protein lineage, which includes the fucoxanthin–chlorophyll proteins (FCP) of the heterokonts and the intrinsic peridinin–chlorophyll proteins (iPCP) of the dinoflagellates. These associations suggest that plastids from the heterokonts, haptophytes, cryptomonads, and the dinoflagellate, Amphidinium, evolved from a red algal-like ancestor. The Chlorarachnion LHC is part of the chlorophyll a/b-binding protein assemblage, consistent with pigmentation, providing further evidence that its plastid evolved from a green algal secondary endosymbiosis. The Chlorarachnion LHC sequences cluster with the green algal LHCs that are predominantly associated with photosystem II (LHCII). This suggests that the green algal endosymbiont that evolved into the Chlorarachnion plastid was acquired following the emergence of distinct LHCI and LHCII complexes. Received: 25 February 1998 / Accepted: 13 May 1998     

Spike timing dependent synaptic plasticity in biological systems

 Association of a presynaptic spike with a postsynaptic spike can lead to changes in synaptic efficacy that are highly dependent on the relative timing of the pre- and postsynaptic spikes. Different synapses show varying forms of such spike-timing dependent learning rules. This review describes these different rules, the cellular mechanisms that may be responsible for them, and the computational consequences of these rules for information processing and storage in the nervous system. Received: 16 January 2002 / Accepted: 3 June 2002 Acknowledgements. This research is supported in part by a National Science Foundation grant IBN 98-08887 (awarded to PDR), and by National Institutes of Health grants R01-MH49792 (awarded to CCB), R01-MH60996 (awarded to CCB), and R01-MH60996 (awarded to PDR). Correspondence to: P. D. Roberts (e-mail: robertpa@ohsu.edu)     

Induction of free radicals in seeds by high intensive flashes and the relevant phosphorus metabolism in the seedling

Influence of high intensive flashes on the yield of free radicals in intact seeds and excised embryonic axis, endosperm, and seed coat, and its resulting effect on seedling growth, total biomass production and phosphorus metabolism in wheat (Triticum aeativum), vetch (Vicia sativa L.) and onion (Allium cepa L.) was studied. Free radicals (f.r.) were formed mainly in seed coat and not in the endosperm. Vetch seeds after irradiation had 20.76 X 10¹³ f.r. g^-1 dry intact seed and 17.30 X 10¹³ f.r. g^-1 dry seed coat. Excised seed coats exposed to irradiation also yielded 17.28 × 10¹³ f.r. g^-1 dry matter. High irradiance “white light” flashes induced more f.r. than a monochromatic one of the same photon content. Red (650 nm), farred (750 nm) and even infra-red (1100 nm) radiation did not initiated f.r. formation but resulted in their decay in samples irradiated earlier by “white”, blue and green parts of the spectrum. Blue irradiation of seeds led to the decrease in the length of shoots and roots in comparison to “white”, green and red irradiation but their biomass increased faster than in the seedlings obtained from non-irradiated or irradiated with “white” and green radiation. The quantity of total acid soluble phosphorus followed a sequence with respect to wavelength of radiation: 436 nm > 650 nm> > 540 nm > non-irradiated > 300–800 nm. Quantity of inorganic phosphorus remained unaffected by different spectral character of radiation. The quantity of organic acid soluble nucleic phosphorus and acid insoluble polyphosphates was higher in samples irradiated with red beams (650 ± 6 nm).     

Halogenating activities detected in Antarctic macroalgae

 Halogenating activities were determined in samples of 18 cultivated species of brown, red and green macroalgae from the Antarctic. Activities for the halogenating organic compounds with bromide, iodide and chloride were found. Investigated red algae (rhodophytes) showed higher brominating and iodinating activities compared to brown (phaeophytes) and green (chlorophytes) algae. The highest brominating and iodinating activities were measured in the red algae Plocamium cartilagineum (1.11±0.01 U g^-1 wet algal weight and 0.18 U g^-1 wet algal weight, respectively) and Myriogramme mangini (3.62±0.17 U g^-1 wet algal weight and 4.5 U g^-1 wet algal weight, respectively). Chlorinating activities were detected in the red alga Plocamium cartilagineum only (0.086 U g^-1 wet algal weight). Received: 12 February 1996/Accepted: 20 June 1996     

Fluorescence spectroscopy of single photosynthetic light-harvesting supramolecular systems

Recent spectroscopic studies of photosynthetic light-harvesting supramolecular complexes at the single supramolecule level are reviewed. This report describes the “single-molecule” investigation on light-harvesting complex 2 (LH2) of purple photosynthetic bacteria, phycobiliproteins of cyanobacteria and red algae, light-harvesting complex 2 (LHC2) of higher plants, and chlorosomes of green photosynthetic bacteria. Unique behaviors and spectral features of single light-harvesting apparatus have been unraveled that were hidden by the ensemble averaging of many of the complexes. The information obtained with be useful for understanding the electronic structures and energy-transfer mechanism of photosynthetic light-harvesting supramolecular systems.     

Spike-timing dependent synaptic plasticity: a phenomenological framework

 In this paper a phenomenological model of spike-timing dependent synaptic plasticity (STDP) is developed that is based on a Volterra series-like expansion. Synaptic weight changes as a function of the relative timing of pre- and postsynaptic spikes are described by integral kernels that can easily be inferred from experimental data. The resulting weight dynamics can be stated in terms of statistical properties of pre- and postsynaptic spike trains. Generalizations to neurons that fire two different types of action potentials, such as cerebellar Purkinje cells where synaptic plasticity depends on correlations in two distinct presynaptic fibers, are discussed. We show that synaptic plasticity, together with strictly local bounds for the weights, can result in synaptic competition that is required for any form of pattern formation. This is illustrated by a concrete example where a single neuron equipped with STDP can selectively strengthen those synapses with presynaptic neurons that reliably deliver precisely timed spikes at the expense of other synapses which transmit spikes with a broad temporal distribution. Such a mechanism may be of vital importance for any neuronal system where information is coded in the timing of individual action potentials. Received: 23 January 2002 / Accepted: 28 March 2002 Correspondence to: W.M. Kistler (e-mail: kistler@anat.fgg.eur.nl Fax: +31 10 408 5459)     

Intracellular optical physiology of the bee's eye

Summary Intracellular optical physiology is a newly developed, non-invasive technique for recording from single types of insect photoreceptor cells. An intact animal is mounted on the goniometer stage of a double-beam, incident-light microspectrophotometer. The stimulating beam delivers monochromatic flashes that evoke pupillary responses from photoreceptor cells in a localized region of the eye. The measuring beam delivers red or infrared illumination that continuously measures the changes in reflectance that accompany the pupillary response. In this paper on the worker bee we demonstrate two experimental conditions under which only one of the three spectral types of photoreceptor dominates the measured response.When the eye is dark-adapted, and increases in reflectance are measured with an infrared beam, threshold responses evoked by long flashes (40 s or more) are dominated by that cell type which is most sensitive to the stimulus. The following data were taken from the dorsal (ventral) poles of the bee's eye: At 350 nm, a quantum flux of 0.1 (0.05)×10 ¹² photons/cm ²/s/numerical aperture of 0.2 produces a threshold response that originates only from the UV-receptors. At 430 nm, a quantum flux of 0.6 (0.2) units produces a threshold response that is dominated by the blue-receptors. At 530 nm, a flux of 1.0 (0.1) units produces a threshold response that originates only from the green-receptors.When the eye is red-adapted, the pupillary responses to short flashes (10 s or less) are dominated by the green-receptors. Under this condition the pupillary action-spectrum for sensitized green-receptors is the same as the electrophysiological spectral sensitivity function of the minimally coupled green-receptor. This is true throughout the spectral range 350 nm–650 nm (Fig. 3).If the duration of stimulating flashes is increased to 40 s, the shape of the action spectrum is unchanged for wavelengths greater than 470 nm, but is significantly elevated, by as much as 1.8 log-units, for wave-lengths less than 420 nm (Fig. 4). In this case the UV-receptors dominate the pupillary response at short wavelengths, while the green-receptors dominate it at long wavelengths.We used these effects to determine that all three spectral types of receptor are present in the regions of both dorsal and ventral poles, as well as in the frontal region of the eye.This work was supported by grants EY01140 and EY00785 from the National Eye Institute, U.S.P.H.S. (to GDB), by the Connecticut Lions Eye Research Foundation (to GDB), and by a grant from the University of Zurich (to RW), and by grant 3.529.075 from the Swiss National Science Foundation (to RW) including a Senior Research Fellowship awarded to GDB. We thank Dr. Thomas Labhart for many helpful discussions and for allowing us to refer to his unpublished data, and Dr. Doekele Stavenga for his critical, constructive comments.     

Variation in the outcome of population interactions: bifurcations and catastrophes

 The nature of the association between two species may vary depending on population abundances, age or size of individuals, or environmental conditions. Interactions may switch between beneficial and detrimental depending on the net balance of costs and benefits involved for each species. We study the repercussion of the ecological setting on the outcomes of conditional or variable interactions by means of a model that incorporates density-dependent interaction coefficients; that is, interaction α-functions. These characterize the responsiveness and sensitivity of the association to changes in partner's abundance, and can take positive and negative values. Variable outcomes – and transitions between them – are categorized as homeo- or allo-environmental, that is, occurring under the same ecological setting, or not, respectively. Bifurcation analyses show that these dynamics are moulded by ecological factors that are: intrinsic to the nature of the association (concerning the sensitivity of the interaction), and extrinsic to the association itself (the quality of the environment referred to each species alone). The influence of these factors may be conflicting; consequently, the dynamics involve catastrophic events. In a facultative variable association, stable coexistence is expected when environmental conditions are adverse; otherwise, the exclusion of one species is the likely outcome. Remarkable situations as the switching of victim-exploiter roles illustrate the theoretical perspective. Received: 15 December 2001 / Revised version: 18 November 2002 / Published online: 28 February 2003 Key words or phrases: Variable population interactions – Conditional interactions – Costs and benefits – Density dependent interaction coefficient – Hysteresis – Symbiosis – Mutualism – Parasitism     

Effects of different excitation and detection spectral regions on room temperature chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence parameters

The effects of different spectral region of excitation and detection of chlorophyll (Chl) a fluorescence at room temperature on the estimation of excitation energy utilization within photosystem (PS) 2 were studied in wild-type barley (Hordeum vulgare L. cv. Bonus) and its Chl b-less mutant chlorina f2 grown under low and high irradiances [100 and 1 000 μmol(photon) m⁻² s⁻¹]. Three measuring spectral regimes were applied using a PAM 101 fluorometer: (1) excitation in the red region (maximum at the wavelength of 649 nm) and detection in the far-red region beyond 710 nm, (2) excitation in the blue region (maximum at the wavelength of 461 nm) and detection beyond 710 nm, and (3) excitation in the blue region and detection in the red region (660– 710 nm). Non-photochemical quenching of maximal (NPQ) and minimal fluorescence (SV₀), determined by detecting Chl a fluorescence beyond 710 nm, were significantly higher for blue excitation as compared to red excitation. We suggest that this results from higher non-radiative dissipation of absorbed excitation energy within light-harvesting complexes of PS2 (LHC2) due to preferential excitation of LHC2 by blue radiation and from the lower contribution of PS1 emission to the detected fluorescence in the case of blue excitation. Detection of Chl a fluorescence originating preferentially from PS2 (i.e. in the range of 660–710 nm) led to pronounced increase of NPQ, SV₀, and the PS2 photochemical efficiencies (F_V/F_M and F_V′/F_M′), indicating considerable underestimation of these parameters using the standard set-up of PAM 101. Hence PS1 contribution to the minimal fluorescence level in the irradiance-adapted state may reach up to about 80 %.     

Internal models for visual perception

 Although the extrapolation of past perceptual history into the immediate and distant future is a fundamental phenomenon in everyday life, the underlying processing mechanisms are not well understood. A network model consisting of interacting excitatory and inhibitory cell populations coding for stimulus position is used to study the neuronal population response to a continuously moving stimulus. An adaptation mechanism is proposed that offers the possibility to control and modulate motion-induced extrapolation without changing the spatial interaction structure within the network. Using an occluder paradigm, functional advantages of an internally generated model of a moving stimulus are discussed. It is shown that the integration of such a model in processing leads to a faster and more reliable recognition of the input stream and allows for object permanence following occlusion. The modeling results are discussed in relation to recent experimental findings that show motion-induced extrapolation. Received: 19 December 2001 / Accepted: 26 November 2002 / Published online: 3 April 2003 Correspondence to: W. Erlhagen (e-mail: wolfram.erlhagen@mct.uminho.pt) Acknowledgements. The author would like to thank D. Jancke for useful discussions and two anonymous reviewers for helpful comments and suggestions on a previous version of this paper. This research was supported by a European grant (IST-2000-29689) and by the Portuguese Science Foundation (POSI/SRI/38051/2001).     

Gene structure of a chlorophyll a/c-binding protein from a brown alga: Presence of an intron and phylogenetic implications

A Laminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chlorophyll a/c-binding protein. Contrary to diatom homologues, the coding sequence is interrupted by an intron of about 900 bp which is located in the middle of the transit peptide. The deduced amino acid sequence of the mature protein is very similar to those of related proteins from Macrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophyll-binding amino acids determined in green plants are also present. Alignments of different sequences related to the light-harvesting proteins (LHC) demonstrate a structural similarity among the three transmembrane helices and suggest a unique ancestral helix preceded by two β-turns. The β-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so than in chlorophyll a/b proteins. Phylogenetic trees generated from sequence data indicate that fucoxanthin-chlorophyll-binding proteins diverged prior to the separation of photosystem I and photosystem II LHC genes of green plants. Among the fucoxanthin-containing algae, LHC I or II families could not be distinguished at this time. Received: 14 February 1996 / Accepted: 4 April 1996     

Photoreceptor spectral sensitivity in island and mainland populations of the bumblebee, <Emphasis Type="Italic">Bombus terrestris</Emphasis>

Most species of flower-visiting Hymenoptera are trichromatic, with photoreceptor spectral sensitivity peaks in the UV, blue and green regions of the spectrum. Red flowers, therefore, should be relatively difficult to detect for such insects. Nevertheless, in population biological studies in the bumblebee, Bombus terrestris, the Sardinian island population (B. t. sassaricus) displayed significantly higher responses to red artificial flowers (in tests of innate colour choice and detectability) than several mainland populations of the same species (Chittka et al. in Cognitive ecology of pollination, pp 106–126, 2001; Popul Ecol 46:243–251, 2004). Since there is relatively little physiological data on population differences in sensory systems, we used intracellular recording to compare photoreceptor spectral sensitivity in B. t. sassaricus and the southern European and Mediterranean population, B. t. dalmatinus. The results show both populations to be UV–blue–green trichromats, but with a small but significant increase in long-wave sensitivity in island bees. Spectral peaks were estimated at 348, 435 and 533 nm (B. t. dalmatinus) and 347, 436 and 538 nm (B. t. sassaricus) for UV, blue and green receptors, respectively. There were no significant differences in UV and blue receptor sensitivities. We found no photoreceptors maximally sensitive to red spectral light in the Sardinian population and model calculations indicate that the behavioural population differences in colour responses cannot be directly explained by receptor population differences. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Noise-tolerant stimulus discrimination by synchronization with depressing synapses

 Some synapses between cortical pyramidal neurons exhibit a rapid depression of excitatory postsynaptic potentials for successive presynaptic spikes. Since depressing synapses do not transmit information on sustained presynaptic firing rates, it has been speculated that they are favorable for temporal coding. In this paper, we study the dynamical effects of depressing synapses on stimulus-induced transient synchronization in a simple network of inhibitory interneurons and excitatory neurons, assuming that the recurrent excitation is mediated by depressing synapses. This synchronization occurs in a temporal pattern which depends on a given stimulus. Since the presence of noise is always a potential hazard in temporal coding, we investigate the extent to which noise in stimuli influences the synchronization phenomena. It is demonstrated that depressing synapses greatly contribute to suppressing the influences of noise on the stimulus-specific temporal patterns of synchronous firing. The timing-based Hebbian learning revealed by physiological experiments is shown to stabilize the temporal patterns in cooperation with synaptic depression. Thus, the times at which synchronous firing occurs provides a reliable information representation in the presence of synaptic depression. Received: 5 July 2000 / Accepted in revised form: 12 January 2001     

Gravity-directed calcium current in germinating spores of Ceratopteris richardii

 Gravity directs the early polar development in single cells of Ceratopteris richardii Brogn. It acts over a limited period of time during which it irreversibly determines the axis of the spore cell's development. A self-referencing calcium selective electrode was utilized to record the net movement of calcium across the cell membrane at different positions around the periphery of the spore during the period in which gravity orients the polarity of the spore. A movement of calcium into the cell along the bottom and out of the cell along the top was detected. This movement was specific, polarized, and strongest in a direction that opposed the vector of gravity. Treatment with nifedipine, a calcium-channel blocker, diminished the calcium current and caused the cell to lose its responsiveness to the orienting influence of gravity. Results shown suggest that calcium plays a crucial role in the ability of a single cell to respond to gravity and in the subsequent establishment of its polarity. Received: 13 June 1999 / Accepted: 1 September 1999     

Developing velocity sensitivity in a model neuron by local synaptic plasticity

Sensor neurons, like those in the visual cortex, display specific functional properties, e.g., tuning for the orientation, direction and velocity of a moving stimulus. It is still unclear how these properties arise from the processing of the inputs which converge at a given cell. Specifically, little is known how such properties can develop by ways of synaptic plasticity. In this study we investigate the hypothesis that velocity sensitivity can develop at a neuron from different types of synaptic plasticity at different dendritic sub-structures. Specifically we are implementing spike-timing dependent plasticity at one dendritic branch and conventional long-term potentiation at another branch, both driven by dendritic spikes triggered by moving inputs. In the first part of the study, we show how velocity sensitivity can arise from such a spatially localized difference in the plasticity. In the second part we show how this scenario is augmented by the interaction between dendritic spikes and back-propagating spikes also at different dendritic branches. Recent theoretical (Saudargiene et al. in Neural Comput 16:595–626, 2004) and experimental (Froemke et al. in Nature 434:221–225, 2005) results on spatially localized plasticity suggest that such processes may play a major role in determining how synapses will change depending on their site. The current study suggests that such mechanisms could be used to develop the functional specificities of a neuron.     

Dynamical synaptic plasticity: a model and connection to some experiments

 Using a modified version of a phenomenological model for the dynamics of synaptic plasticity, we examine some recent experiments of Wu et al. [(2001) J Physiol 533:745–755]. We show that the model is quantitatively consistent with their experimental protocols producing long-term potentiation (LTP) and long-term depression (LTD) in slice preparations of rat hippocampus. We also predict the outcome of similar experiments using different frequencies and depolarization levels than reported in their results. Received: 3 September 2002 / Accepted in revised form: 22 October 2002 / Published online: 24 February 2003 Correspondence to: H.D.I. Abarbanel (e-mail: hdia@jacobi.ucsd.edu) Acknowledgements. We are very grateful to A. Selverston and D. Feldman for conversations about this work. This work was partially supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Engineering and Geosciences, under grants No. DE-FG03-90ER14138 and No. DE-FG03-96ER14592, by a grant from the National Science Foundation, NSF PHY0097134, by a grant from the Army Research Office, DAAD19-01-1-0026, by a grant from the Office of Naval Research, N00014-00-1-0181, and by a grant from the National Institutes of Health, NIH R01 NS40110-01A2. This work was also partially supported by M. Ciencia y Tecnologa BFI2000-0157 (R.H.).     

PHENOTYPIC PLASTICITY EARLY IN LIFE CONSTRAINS DEVELOPMENTAL RESPONSES LATER

Abstract.— Plastic stem‐elongation responses to the ratio of red:far‐red (R:FR) wavelengths enable plants to match their phenotype to local competitive conditions. However, elongation responses early in the life history may occur at the cost of reduced plasticity later in the life history, because elongation influences both allocation patterns and structural integrity. A common‐garden experiment was performed to test whether seedling responses to R:FR affect biomass allocation, biomass accumulation, and subsequent plasticity to the cue. Seedlings of Abutilon theophrasti were stimulated to elongate by low R:FR treatments, and subsequent growth and plasticity was compared with nonelongated individuals. Elongated seedlings were less responsive than nonelongated ones to a second bout of low R:FR. Thus, seedling plasticity to R:FR reduces subsequent responsiveness to this cue. This negative association across life‐history stages suggests an important constraint on the evolution of plastic stem responses, because selection in A. theophrasti has previously been shown to favor increases in early elongation in combination with increased later elongation. The reduced responsiveness of elongated seedlings to R:FR appeared to result from a structural feedback mechanism, indicating that the opportunity cost of early responses may be lower in environments providing structural support.