Plant, Cell & Environment

In Pteris vittata, an arsenic (As) hyperaccumulator, As application enhanced the uptake of SO₄²⁻, which was used for low-molecular-weight thiol synthesis in fronds. Moreover, sulphur (S) absorbed with As accumulated locally in a vacuole-like organelle in epidermal cells of fronds, whereas S absorbed alone was distributed uniformly. Thus, this study demonstrates that As has a dramatic impact on the metabolisms and accumulation of S in P. vittata.

This review summarizes the emerging roles of amino acid metabolic pathways in plant immunity. In particular, the significance of pipecolic acid in systemic acquired resistance, the roles of proline metabolism and polyamine oxidation in ROS generation, the function of aspartate-derived pyridine nucleotide metabolism in pre- and post-invasion defense, amino acid imbalances in the aspartate pathway leading to oomycete resistance, and the influence of amino acid acylation on plant pathogen and pest resistance are highlighted.

In Medicago truncatula / Sinorhizobium meliloti symbiotic nodules, we measured in vivo, using pH sensitive ratiometric probe, the pH of peribacteroid space (PBS) during the whole symbiotic process. We observed a progressive acidification of the PBS from zone II to zone III. Furthermore, PBS acidification and nodule functioning were disrupted by various treatments including abiotic stresses, symbiosis defective strains and pharmacological inhibitors.

This paper is important because it offers examples of how simulation models can be used to develop understanding and predict how crops respond to environmental factors. It also presents and utilises a new concept, the Kaya-Porter identity, as a means of deconstructing biological use efficiencies into component parts as a stimulus to new thinking, models and experiments in crop physiology.

The last decade has provided breakthrough discoveries in phytohormone sensing and signal transduction, and highlighted the striking mechanistic similarities between the auxin and jasmonate (JA) signalling pathways, two hormones that regulate diverse aspects of plant growth, development and interaction with the environment. In this review, we list each important element from the ‘core JA perception and early signalling module’, discuss their function and role in the JA-cascade, to which protein family they belong and how striking it is that many of the closely related proteins function in another phytohormonal signalling cascade, that is of the auxins. We discuss the correlation and relevance of the sequence similarities and divergence with regard to the functioning of the respective proteins in the respective signalling cascades.

The mechanistically based leaf photosynthesis model has played a major role in defining the path toward scientific understanding of photosynthetic carbon uptake and the role of photosynthesis on regulating the earth's climate and biogeochemical systems. This review summarizes the photosynthesis model, including its continued development and applications. We also review the implications these developments have on quantifying photosynthesis at a wide range of spatial and temporal scales, and discuss the model's role in determining photosynthetic responses to changes in environmental conditions.

The early development of maize plants in Western and Central Europe can be strongly impaired by the cold spells occurring during spring. Yet, selection for maize varieties with enhanced chilling tolerance is difficult due to climatic fluctuations and the sensitive response of maize plants to low temperatures. By performing high-resolution genome-wide association mapping in a diverse panel of maize inbred lines evaluated in controlled environments as well as in field experiments, we identified several genomic regions involved in chilling tolerance and early growth. Candidate genes frequently involved in signaling or gene expression regulation provide a key for understanding the complex mechanisms underlying chilling tolerance and this knowledge promises to facilitate breeding of chilling tolerant varieties with enhanced yield stability under unfavorable climatic conditions.

The lack of dependable morphological indicators for developmental transitions during seed growth has hindered modeling work in the common bean (Phaseolus vulgaris L.). This study presents a mathematical analysis of several key reproductive growth and development traits for the common bean. Reliable morphological indicators for the onset and end of the rapid seed growth phase were identified, expanding existing developmental indices. Previously undocumented differences between genotypes of distinct genepools suggest broad genetic variation and independent genetic control of pod and seed growth dynamics.

Ammonium nutrition has been suggested to be associated with alterations in the oxidation-reduction state of leaf cells. Herein, we show that ammonium nutrition in Arabidopsis thaliana increases leaf NAD(P)H/NAD(P)⁺ ratio, reactive oxygen species content, and accumulation of biomolecules oxidized by free radicals. We also showed that ammonium nutrition changes mitochondrial electron transport chain activity, increasing mitochondrial reactive oxygen species production. Our results indicate that the functional impairment associated with ammonium nutrition is mainly associated with redox reactions outside the chloroplast.

This article comments on: Dynamic secretion changes in the salt glands of the mangrove tree species Avicennia officinalis in response to a changing saline environment

Although respiration is a major contributor to the net exchange of CO₂ between plants and the atmosphere, it would be desirable to take a holistic view of the network when modelling the process and to consider all the potential contributors to light-independent CO₂ balance. We argue that flux balance analysis of genome-scale metabolic models offers a practicable tool for predictive modelling of net CO₂ evolution. This is supported by the encouraging agreement that has been found between the experimental results obtained by metabolic flux analysis and the predictions of flux balance analysis. While there is scope for further improvement, particularly in the way in which flux balance analysis handles cell maintenance costs, its power is already sufficient to make useful predictions about the impact of environmental factors on CO₂ production by plant tissues.

Exploration of natural variation in salinity response of plants facilitates the analysis of gene and trait association. Three population structures were identified in 56 accessions of perennial ryegrass (Lolium perenne L.) accounting for 11% of phenotypic trait variations under 300 mM NaCl treatment. Significant associations were found between LpNHX1 and leaf K⁺/Na⁺ under both control and salinity stress after controlling population structures. These results indicate allelic variation in LpNHX1 may affect salinity tolerance of perennial ryegrass.

The arbuscular mycorrhizal (AM) symbiosis is widespread throughout the plant kingdom but most terrestrial ecosystems also contain a considerable number of non-mycorrhizal plants. The interaction of such non-host plants with AM fungi is still poorly understood. In this study, we investigated whether the non-mycorrhizal plant Arabidopsis thaliana, the model organism for plant molecular biology and genetics, interacts with AM fungi. We demonstrate, for the first time, that the presence of fungal networks formed by the AM fungus Rhizophagus irregularis reduces A. thaliana growth by 50% or more. In addition, by using bright field, confocal and electronic microscopy we show that this fungus can colonize roots of A. thaliana, although arbuscules were never observed. These results reveal high susceptibility of A. thaliana to R. irregularis, suggesting that A. thaliana is a suitable model plant to study non-host/AM fungi interactions and the biological basis of AM incompatibility.

Commentary: Interactions between arbuscular mycorrhizal and non-mycorrhizal plants: do non-mycorrhizal species at both extremes of nutrient-availability play the same game?

This study includes an extended RNAseq analysis of the locally induced defence responses in leaves of lettuce after inoculation with Botrytis cinerea, an economically important pathogen affecting many dicot plant species. To our knowledge, this is the first reported quantitative transcriptomic study of lettuce, which was possible after the recent unravelling of the lettuce genome. The observed high number of differentially expressed genes allowed us to classify them according to the biological pathways indicating the induction of secondary metabolism, with the phenylpropanoid pathway and terpenoid biosynthesis among the most pronounced responses. Subsequent qRT-PCR-based gene expression analysis on a limited set of genes resulting from our RNAseq-study revealed a high similarity in (i) the response in locally infected versus systemic leaves and (ii) in the induction of similar pathways during compatible interactions of lettuce with necrotrophic versus biotrophic pathogens.

We have investigated the role of LeNHX2, an endosomal class-II NHX transporter, in salt tolerance of tomato plants. Overexpression of LeNHX2 in tomato improves NaCl tolerance, decreased cytosolic K⁻ and induced K⁻ uptake by roots. The results suggest that LeNHX2 improves NaCl tolerance by regulating the activities of K⁻ transport systems possibly through modulation of cytosolic K⁻ levels.

Rice seedlings grown on germination paper in red-light (400 μmoles photons m⁻² s⁻¹) for 48 h having their shoot-bottom exposed had suppressed photomorphogenesis and were deficient in chlorophyll. Seedlings grown under identical light regime having their shoot-bottom covered in vermiculite or in aluminum foil were green and accumulated chlorophyll. The phyA mutant seedlings grown in red-light having their shoot-bottom exposed were green and accumulated chlorophyll along with the up regulated Chl biosynthesis intermediates. The red-light-induced suppression of photomorphogenesis, perceived in the shoot bottom, is a red-HIR response of PhyA.

• Intercropping of maize and peanut significantly improves iron nutrition of peanut in calcareous soils.
• This work gives new insights on how Strategy I plants use Fe(III)–MAs from graminaceous plants at the molecular level.
• The phytosiderophore deoxymugineic acid (DMA) was detected in the roots of intercropped peanuts and also the Fe(III)–DMA transporter AhYSL1 was identified in peanut roots.
• Fe(III)–DMA dissolved by maize might be absorbed directly by neighboring peanuts in the peanut/maize intercropping system.

Using the transgenic Arabidopsis and transgenic BY-2 cell systems, we showed that OsYchF1 plays a negative role in salinity stress response, probably via suppression of the anti-oxidation enzymatic activities, resulting in lipid peroxidation and accumulation of ROS. Its interaction partner OsGAP1 plays an opposite role. We also demonstrated the homologue of OsYchF1 and OsGAP1 in Arabidopsis thaliana (AtYchF1 and AtGAP1, respectively) may play similar roles as their rice counterparts. Therefore, our works have added new dimensions to the functional roles of plant YchF proteins and their regulators.

The present report reveals a significant influence for growth day length conditions in determining the phenotypic outcome of Arabidopsis exposed to O₃. Loss of cytosolic NADP-isocitrate dehydrogenase function (knockout icdh mutant) did not markedly affect the response to O₃, likely reflecting redundancy with other cytosolic NADPH-producing enzymes. Unlike icdh, a knockout mutant for glutathione reductase 1 (GR1) strongly affected the response by decreasing O₃-triggered lesions, salicylic acid accumulation and induction of PR1. Thus, the GR1-glutathione system seems to play novel signalling roles during ozone exposure.

Mesophyll conductance (g_m) is now recognised as a key limitation of photosynthesis that should be incorporated into canopy-level models of C exchange. Variation in g_m through the canopy of trees has been investigated, but we do not know if water stress affects equally g_m of all canopy layers. We investigated limitations to photosynthesis at different heights in a mixed adult stand of Quercus petraea and Fagus sylvatica trees during a moderately dry summer. Drought-induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought-induced increases in mesophyll limitations were largest in leaves from the lowest canopy.

Knowledge of how environment influences juvenility could help with crop scheduling in commercial horticulture, decrease time to flowering and reduce waste with resulting benefits for the environment through lower inputs and energy required per unit of marketable product.

In the manuscript, using an experimental assay that allows the length of the juvenile phase to be estimated in response to floral competence, and several mutants impaired in different genetic pathways, we show that multiple inputs influence the timing of the juvenile-to-adult phase transition in Arabidopsis.

In the challenge to increase photosynthetic rate per leaf area steady state models of photosynthesis provide not only tools for gas exchange analysis but also for thought experiments that can explore photosynthetic pathway changes. These include redirecting photorespiratory CO₂, inserting bicarbonate pumps into C₃ chloroplasts or inserting C₄ photosynthesis into rice. Here a number of models derived from the C₃ model by Farquhar, von Caemmerer and Berry are discussed and compared.

Although previous work has showed that leaf ageing reduced stomatal sensitivity to ABA (Atkinson et al. 1989; J. Exp Bot), study here is the first report which suggested that alterations in ethylene signalling are involved in this diminished response. Soil drying or ABA-induced stomatal closure of aged leaves was partly restored by pre-treating plants with 1-methylcyclopropene (1-MCP) which antagonizes ethylene receptors; or by inoculating soil around the roots with the rhizobacterium Variovorax paradoxus 5C-2 which has been shown that it can decrease concentrations of the immediate biosynthetic precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC). Although old leaves showed similar ACC concentrations comparing to young leaves, they also showed a greater sensitivity of stomata to ethylene. Since old leaves continue to transpire despite lower photosynthetic rates (Atkinson et al. 1989; J. Exp Bot), our results suggest that management options to increase leaf water use efficiency and potentially crop water use efficiency, which may be of crucial importance when water supplies are limiting.

Genetics of plant adaptations to arsenic stress are poorly understood. To probe plant responses to aresnite-induced oxidative stress, Arabidopsis thaliana wild type, and mutants impaired in auxin transport were studied. This research showed that auxin transport is important for plant tolerance to arsenite and auxin transporter AUX1 has a positive role on plant tolerance to arsenite via ROS mediated signaling.

Meristem temperature drives plant development but is hardly ever quantified. Instead, air temperature is usually used as its approximation. We provide evidence that meristem temperature can substantially deviate from air temperature, even under moderate environments in a species-specific way. This study indicates that for properly linking growth and development of plants to temperature in future applications, for instance in climate change scenarios studies, T_meristem should be used instead of T_air, as a species-specific trait highly reliant on various environmental factors.

It was difficult to measure optical properties (reflectance and transmittance spectra) of narrow grass leaves and conifer needles by using a typical integrating sphere. We propose a new measurement protocol and calculation algorithms. The protocol does not damage sample leaves and is valid for various types of leaves, young leaves, mature green leaves and senescent leaves.

The culms of the reed plant take up water and salt from brackish habitat water by fine laterals of the highly branched adventitious roots at the basal nodes. In this study it was found that the radial flux of water through these roots did not exert a true solvent drag to NaCl, thus indicating the absence of an effective hydraulic bypath through the apoplast. Results indicate further that the endodermis is the most significant barrier for radial apoplastic solute diffusion in the fine laterals, the main mechanism of NaCl-uptake from a saline environment. A high steady state concentration of NaCl in the xylem vessels of the fine lateral roots reduces the osmotic effect of the saline environment on water uptake.

Pretreatment with the NO donor sodium nitroprusside (SNP) improved survival percentage of maize seedlings and alleviated an increase in electrolyte leakage and decrease in tissue vitality as well as accumulation of malondialdehyde. In addition, pretreatment with SNP enhanced the activity of L-cystine desulfhydrase, which in turn induced accumulation of endogenous H₂S, while application of H₂S donors, NaHS and GYY4137, increased endogenous H₂S content, followed by mitigating increase in electrolyte leakage and enhancing survival percentage of seedlings under heat stress. Interestingly, SNP-induced heat tolerance was enhanced by application of NaHS and GYY4137, but eliminated by inhibitors of H₂S synthesis DL-propargylglycine, aminooxy acetic acid, potassium pyruvate and hydroxylamine, and the H₂S scavenger hypotaurine.

In this study, we show ion profiles in the xylem and leaf tissue, concerning with the physiological function of epithem cells of hydathode in ion metabolism in a barley primary leaf. Combination of physiological measurements of ion contents, visualization of cell functions and expression measurements of transporters along longitudinal leaf tissue suggested that a plant leaf has a new aspect involving with inorganic ion metabolism.

While the distribution of nitrogen isotopes in the biosphere has the potential to offer insights into the past, present, and future dynamics of the nitrogen cycle, to date many of the patterns along the soil-plant-atmosphere continuum have eluded interpretation. Here, we describe a new approach for modeling isotope fractionation in complex systems, as well as a new model of nitrogen isotope fractionation during leaf-atmosphere NH_3(g) exchange. The results suggest that this often overlooked mechanism contributes meaningfully to variation in the nitrogen isotopic composition of organic nitrogen in plants as well as NH_3(g) in the atmosphere, and should be considered in analyses of the distribution of nitrogen isotopes at natural abundance and tracer levels.

To investigate whether leaf gas-exchange rates and sensitivity to drought acclimate to precipitation regimes, we compared the seasonal variations of leaf gas-exchange in mature piñon pine and juniper across three different precipitation treatments: ambient precipitation, irrigation (+30% of ambient precipitation), and partial rainfall exclusion (−45%). Treatments significantly affected leaf water potential, stomatal conductance and photosynthesis for both isohydric piñon and anisohydric juniper. Despite their distinct drought resistance strategies, hydraulic limitation on leaf gas-exchange and acclimation to the precipitation regimes occurred in both species, leading to an intra-specific trade-off between maximum photosynthetic assimilation and resistance of photosynthesis to drought. This response will be most detrimental to the carbon balance of piñon under predicted increases in aridity in the southwestern USA.

Under natural conditions, plants are subjected to continuous changes of irradiance that drive variations of stomatal conductance (g_s). We propose a new dynamic model to predict the temporal response of g_s to irradiance. Compared with widely used steady-state models our dynamic model described daily time courses of g_s with a higher accuracy. In particular, it was able to describe the hysteresis of g_s responses to irradiance and the resulting rapid variations of intrinsic water-use efficiency.

The importance of the work: A brief summary statement (3-4 sentences maximum)

This should explain the motivation for the work and summarize the findings

It has been suggested that Arabidopsis thaliana can absorbed formaldehyde (HCHO) and oxidize it to formate (HCOOH). This study investigated the role of the C1 metabolism and the Calvin Cycle during H¹³CHO-metabolism in Arabidopsis. The results revealed two metabolic pathways of H¹³CHO: one was assimilated by the Calvin Cycle to produce [U-¹³C]Gluc; another was metabolized in the C1 metabolism to generated [3-¹³C]Ser. Both the Calvin Cycle and C1 metabolism functioned simultaneously and dependently during HCHO-metabolism in Arabidopsis.

Plant roots exposed to drying soil synthesise chemical signals such as ABA, which move from the roots to the shoots to limit transpiration, thereby increasing leaf water use efficiency. Our work tests alternative hypotheses as to how vertical soil moisture gradients quantitatively affect xylem ABA concentration. Unlike split-root experiments where xylem ABA concentration depended on both the soil water content of each compartment and the fractional water uptake from each (Dodd et al. 2008; Plant Cell Env. 31, 1263–1274), when plants are exposed to dry upper soil and moist soil at depth (as is typical of many field conditions), xylem ABA concentration was best predicted by average soil water content in the entire root-zone, because root ABA concentration was homogeneous across the root-zone and related to bulk root water potential. These results will help understand the physiological effects of different water-saving irrigation techniques applied in the field, where vertical gradients are an important source of soil moisture heterogeneity.

To understand organelle positioning under cold conditions, we studied cold-induced organelle relocation in the liverwort Marchantia polymorpha L. Cold-induced relocation movements of chloroplasts, nuclei and peroxisomes, but not mitochondria, were found in living liverwort cells. Our findings suggest that several organelles concurrently change their positions to cope with cold temperature.

This article comments on: Transpiration rate relates to within- and across-species variations in effective path length in a leaf water model of oxygen isotope enrichment

This report demonstrates that Processing Bodies (PBs) and Stress Granules (SGs) localized Arabidopsis tandem CCCH zinc finger protein AtTZF4, 5, and 6 are positive regulators for ABA- and negative regulators for light- and GA-mediated seed germination responses. AtTZF4, 5, and 6 affect seed germination by controlling genes critical for ABA and GA response.

Diverse approaches have been developed in order to analyse metabolic fluxes. These can be broadly divided into stationary methods which require that the system under study is at isotopic as well as metabolic steady state and instationary methods for which only metabolic steady state is a pre-requisite. Here we review the use of instationary methods to interrogate plant metabolism and its regulation.

We investigated whether native AMF isolated from a Mediterranean saline area can help maize plants to overcome the negative effects of salinity stress better than non-AM plants or plants inoculated with non-native AMF. Plants inoculated with the native AMF had the highest shoot dry biomass at all salinity levels and showed increased K⁺, reduced Na⁺ accumulation and enhanced K⁺/Na⁺ ratios in their tissues. For the first time, these effects have been correlated with regulation of ZmAKT2, ZmSOS1 and ZmSKOR genes expression in maize roots, contributing to K⁺ and Na⁺ homeostasis in plants colonized by native AMF.

Glycine decarboxylase complex (GDC), which is composed of P-, H-, T- and L-protein subunits, is ubiquitous in all organisms from bacteria to eukaryotic cells. While structural analysis has demonstrated that the H subunit of GDC (GDCH) plays a pivotal role in GDC, the biological role of GDCH in plant species is seldom reported. The present study investigated the function of the OsGDCH, stresses that result from knockdown of OsGDCH, and the interactions of these stresses with other cellular processes in rice plants through RNA interference (RNAi). Our results show that the OsGDCH is a typical photorespiratory gene and the severely suppressed OsGDCH-RNAi plants display a senescence syndrome under ambient CO₂; senescence in the OsGDCH-RNAi rice plants is induced by ROS, and transcription factor OsWRKY72 may mediate the ROS-induced senescence.

BRI1 mediated brassinosteroid signaling in Arabidopsis is suitable for mathematical modeling approaches. This can be helpful to position the components of the BR signalosome and to understand and interpret its complex biological output. The focus of this review is on a number of recent modeling studies. Future developments will require additional quantitative data, to be generated using fluorescently labeled reporters.

Abscisic acid (ABA)-, stress-, and ripening-induced (ASR) proteins are reported to be involved in abiotic stresses. However, it is not known whether ASR genes confer drought stress tolerance by utilizing the antioxidant system. The findings of this study demonstrated TaASR1 function in drought/osmotic stress tolerance. TaASR1 conferred drought/osmotic stress tolerance through regulating the expression of stress-, and defense-associated genes and enhancing the antioxidant system, thus preventing plants from oxidative damage.

In an effort to understand the role of metabolism in photoacclimation in Chlamydomonas reinhardtii, we used NMR and GC-MS to assess changes in the aqueous metabolome following a shift to excess light. Amino acid pool sizes increased significantly in response to high light along with pathways downstream of photorespiration. Our results suggest metabolism is pliable, has a critical role in coping with the energetic imbalance during excess light exposure, and a necessary adjustment to support an increased growth rate that is an effective energy sink for the excess reducing power generated during light stress.

Members of the conserved gigantea (gi) gene family act in the plant circadian system and regulate multiple aspects of development. The maize gigantea1 (gi1) gene is the more highly expressed of two gi homeologs in the maize genome and its function is previously uncharacterized. Analysis of maize gi1 mutants demonstrates that this gene is part of the signaling networks controlling flowering time, phase change, and growth. These discoveries reveal the importance of circadian genes in the regulation of maize growth and development.

This paper highlights the effects of hydrogen sulfide on plants, and discusses the evidence that this gas can be considered as a signalling molecule. Plants can be shown to generate hydrogen sulfide and respond to it, with recent work pointing to the possibility that hydrogen sulfide may modify protein thiol groups. This would mean that hydrogen sulfide may be in competition with reactive oxygen species and nitric oxide in its potential signalling role.

This work examined a winter-drought induced dieback at the Scots pine's southern edge through a dual-isotope approach (Δ¹³C and δ¹⁸O in tree-ring cellulose). Declining trees showed a stronger coupling between climate, growth and intrinsic water-use efficiency (WUEi) than non-declining individuals, which was likely associated with their native aptitude to grow more, take up more water and, also, exhibit a greater cavitation risk. This indicated that co-occurring individuals were differentially predisposed to winter-drought mortality.

Along many western North American rivers, human-altered flow patterns have led to reduced cottonwood seeding recruitment, and seedling death is often attributed to water stress. This study examined photosynthetic responses of Fremont cottonwood to the interactive effects of water, light, and heat stresses, which were hypothesized to be more important than water stress alone on the exposed point bar environments where seedlings establish. Our results show that interactions of heat stress, surprisingly mediated by reduced photosynthetic capacity and not damage to photosystems, water limitation and leaf orientation are important in determining stress to cottonwood leaves that leads to leaf death and eventual seedling mortality. Application of these results to modeling efforts is needed because current models of riparian seedling establishment use water stress alone as a limiting factor.

Network analysis depicts biological systems and behaviours from omics data, enabling us to extract biological meaning and predict gene function. Genes involved in specialized metabolism are often co-ordinately regulated at the transcriptional level. We review advances in gene co-expression and gene-to-metabolite network analysis in Arabidopsis and non-model plant species from a viewpoint of gene discovery in plant specialized metabolism.

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. Here, we examined the salt glands of a tropical mangrove tree species (Avicennia officinalis) as putative salt and water bi-regulatory units that can respond swiftly to altering environmental cues. We uncovered rhythmic fluctuations of salt gland secretion rates that could be reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re-absorption of water during salt removal in A. officinalis salt glands, an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.

Commentary:The devil in the detail of secretions

In this review, emphasis is paid to (1) the emerging role of sugars (and derivatives) as antioxidants and (2) the role of organelles, with special attention for the vacuole in the cellular redox network.

Our understanding of desiccation tolerance in lichens, and of their chlorobionts, was limited to the ability of the antioxidant system to protect cells from photo-oxidative and dehydration induced damage. He intent of this investigation was to determine how desiccation tolerance in the algal partner, Asterochloris erici, of the symbiosis was broadly controlled, a critical missing piece of information in our understanding of the evolution of this important trait in plants. Using a proteomic approach, along with targeted transcript profiling, we were able to demonstrate that only a small number of proteins, including Hsp90s and β-tubulins, were positively enhanced during dehydration indicating that the desiccation tolerance in the alga is primarily constitutive. These conclusions were consistent with ultrastructural observations that revealed extensive damage, especially when drying rates were rapid, that the alga survived without a major alteration of the proteome.

The chemical mechanism of Rubisco is at the heart of photosynthetic metabolism since it dictates the rate of carboxylation. Here, advantage is taken of chemical formalism to give general equations describing carboxylation velocity, specificity and isotope effects. The limits of these and uncertainties on intrinsic chemical events are discussed so as to appreciate possibilities of optimization.

Molecular interaction between NRT2.1 transcript levels and the ethylene signaling pathway under nitrate deficiency is still elusive. Here, we report a low nitrate (LN) treatment-induced rapid burst of ethylene production and regulated expression of ethylene signaling components CTR1, EIN3 and EIL1 in wild-type Arabidopsis thaliana (Col-0) seedlings, and enhanced ethylene response reporter EBS:GUS activity in both Col-0 and the ethylene mutants ein3-1eil1-1 and ctr1-1. Comparison of ethylene production and EBS:GUS activity between nrt1.1, nrt2.1 mutants and Col-0 indicated that this up-regulation of NRT2.1 expression caused a positive effect on ethylene biosynthesis/signaling under LN treatment, and ethylene down-regulated NRT2.1 expression and reduced the high-affinity nitrate uptake. Together, these findings uncover a negative feedback loop between NRT2.1 expression and ethylene biosynthesis/signaling under nitrate deficiency, which may contribute to finely tuning of plant nitrate acquisition during exploring dynamic soil conditions.

The manuscript shows clearly that NtHXK1 is not only crucial for maintaining glycolytic activity during respiration but also for regulating starch turnover, especially during the night. Additionally, we provide evidence that NtHXK1 also acts as glucose sensor in Arabidopsis. For the first time, the performance of a distinct metabolic function in addition to a sugar sensing function of a plant hexokinase could be demonstrated.

Commentary: The multifaceted relationship between leaf water 18O enrichment and transpiration rate

Current understanding of the mechanistic controls on stable oxygen isotope ratio of leaf water (δ¹⁸O_L) does not provide complete characterization of effective pathlength (L) of the Péclet effect, – a key component of the leaf water model. In this study, we collected diurnal and seasonal series of leaf water enrichment and estimated L in 6 field-grown angiosperm and gymnosperm tree species. Our results suggest a pivotal role of leaf transpiration rate (E) in driving both within- and across-species variations in L. Our observation of the common presence of an inverse scaling of L with E in the different species therefore cautions against: i) the conventional treatment of L as a species-specific constant in leaf water or cellulose isotope (δ¹⁸O_p) modeling; and ii) the use of δ¹⁸O_p as a proxy for g_s or E under low E conditions.

The response of leaf energy metabolism to temperature is central to predicting the impact of environmental gradients and future climate regimes on carbon exchange in forests. Here, we tested whether Eucalyptus pauciflora (an evergreen, broadleaved tree) growing in thermally contrasting environments (including winter-acclimated trees encased in ice at high altitudes) exhibit generalizable temperature response functions of leaf respiration and fluorescence. We found that leaf energy metabolism was surprisingly heat tolerant (with maximal rates of respiration occurring at 51–57°C), with temperature responses varying seasonally. Collectively, our results: (1) highlight high-temperature limits of energy metabolism in E. pauciflora; and, (2) provide a framework for improving representation of T-responses of leaf respiration in predictive models.

The capacity to consume excess photosynthetic electrons by PTOX activity was investigated in R. glacialis shade- and sun-leaves. PTOX protein content was highest in sun-leaves and correlated to electron consumption attributed to PTOX. In R. glacialis leaves, PTOX may act as safety valve to prevent overreduction of the electron transport chain and photoinhibition under conditions of varying light and temperature in the alpine environment.

In the manuscript entitled “Differential expression of specific sulphate transporters underlies seasonal and spatial patterns of sulphate allocation in trees” we examined the importance of sulphate transporter for seasonal sulphate storage and mobilisation in the wood of poplar. For this purpose we related seasonal gene expression patterns of specific sulphate transporter genes to sulphate contents in xylem sap and wood. Together with the previously published model for seasonal sulphate circulation between bark and leaf tissues of poplar (Dürr et al., 2010) these results provide information for future mechanistic modelling of whole tree sulphate fluxes.

A recombinant inbred line population for the accessions C24 and Tenela (Te), showing large variation in freezing tolerance, was established to study genetic determinants of cold acclimation capacity inArabidopsis thaliana. Mapping of quantitative trait loci (QTL) revealed three QTL regions on chromosomes 2, 4 and 5. With the aid of gene expression data, the Myb family transcription factor REVEILLE1 (At5g17300) on chromosome 5 was identified as a novel negative regulator of freezing tolerance in Arabidopsis.

The potential for model-data synthesis is growing in importance as we enter an era of ‘big data’, greater connectivity, and faster computation. Realizing this potential requires that the research community broaden its perspective about how and why they interact with models. We provide a review and perspective on the statistics and informatics of model-data fusion in plant biology. Overall we promote a community-based paradigm to model-data synthesis and highlight some of the tools and techniques that facilitate this approach.

Although the process of photosynthesis from light capture to carbohydrate synthesis has been largely known for some time, a complete dynamic process model representing each discrete step has been lacking. e-Photosynthesis described here provides this platform and is shown to reproduce in silico, quantitatively and qualitatively, responses of leaf gas exchange, electron transport, chlorophyll fluorescence and biochemical fluxes observed in vivo. The model provides a design engineering tool for selecting targets in a system of over 100 potential targets and many thousands of permutations.