5,550 research outputs found
A Mathematical model to guide Genetic Engineering of Photosynthetic Metabolism
open5noThe optimization of algae biomass productivity in industrial cultivation systems requires genetic improvement of wild type strains isolated from nature. One of the main factors affecting algae productivity is their efficiency in converting light into chemical energy and this has been a major target of recent genetic efforts. However, photosynthetic productivity in algae cultures depends on many environmental parameters, making the identification of advantageous genotypes complex and the achievement of concrete improvements slow. In this work, we developed a mathematical model to describe the key factors influencing algae photosynthetic productivity in a photobioreactor, using experimental measurements for the WT strain of Nannochloropsis gaditana. The model was then exploited to predict the effect of potential genetic modifications on algae performances in an industrial context, showing the ability to predict the productivity of mutants with specific photosynthetic phenotypes. These results show that a quantitative model can be exploited to identify the genetic modifications with the highest impact on productivity taking into full account the complex influence of environmental conditions, efficiently guiding engineering efforts.embargoed_20181201Perin, Giorgio; Bernardi, Andrea; Bellan, Alessandra; Bezzo, Fabrizio; Morosinotto, TomasPerin, Giorgio; Bernardi, Andrea; Bellan, Alessandra; Bezzo, Fabrizio; Morosinotto, Toma
A rule-based functional-structural model of rice considering source and sink functions
As a first step towards a generic genotype-phenotype model of rice, we present here a model of the growth and morphology of rice in combination with ecophysiological processes using the technique of functional-structural plant modelling (FSPM) and the interactive modelling platform GroIMP along with the graph-based Relational Growth Grammar formalism. The model constitutes a simple yet functionally coherent phenotype model of rice, consisting of a set of morphogenetic RGG rules describing an “average” developmental course and final morphology, partially linking yield traits to processes (tiller and grain number, stem length, grain filling rate, grain weight)
Adjustment of carbon fluxes to light conditions regulates the daily turnover of starch in plants : a computational model
Peer reviewedPublisher PD
Cryptic photosynthesis, Extrasolar planetary oxygen without a surface biological signature
On the Earth, photosynthetic organisms are responsible for the production of
virtually all of the oxygen in the atmosphere. On the land, vegetation reflects
in the visible, leading to a red edge that developed about 450 Myr ago and has
been proposed as a biosignature for life on extrasolar planets. However, in
many regions of the Earth, and particularly where surface conditions are
extreme, for example in hot and cold deserts, photosynthetic organisms can be
driven into and under substrates where light is still sufficient for
photosynthesis. These communities exhibit no detectable surface spectral
signature to indicate life. The same is true of the assemblages of
photosynthetic organisms at more than a few metres depth in water bodies. These
communities are widespread and dominate local photosynthetic productivity. We
review known cryptic photosynthetic communities and their productivity. We link
geomicrobiology with observational astronomy by calculating the disk-averaged
spectra of cryptic habitats and identifying detectable features on an exoplanet
dominated by such a biota. The hypothetical cryptic photosynthesis worlds
discussed here are Earth-analogs that show detectable atmospheric biomarkers
like our own planet, but do not exhibit a discernable biological surface
feature in the disc-averaged spectrum.Comment: 23 pages, 2 figures, Astrobiology (TBP) - updated Table 1, typo in
detectable O2 correcte
Phenotypic landscape inference reveals multiple evolutionary paths to C photosynthesis
C photosynthesis has independently evolved from the ancestral C
pathway in at least 60 plant lineages, but, as with other complex traits, how
it evolved is unclear. Here we show that the polyphyletic appearance of C
photosynthesis is associated with diverse and flexible evolutionary paths that
group into four major trajectories. We conducted a meta-analysis of 18 lineages
containing species that use C, C, or intermediate C-C forms of
photosynthesis to parameterise a 16-dimensional phenotypic landscape. We then
developed and experimentally verified a novel Bayesian approach based on a
hidden Markov model that predicts how the C phenotype evolved. The
alternative evolutionary histories underlying the appearance of C
photosynthesis were determined by ancestral lineage and initial phenotypic
alterations unrelated to photosynthesis. We conclude that the order of C
trait acquisition is flexible and driven by non-photosynthetic drivers. This
flexibility will have facilitated the convergent evolution of this complex
trait
Surface and Temporal Biosignatures
Recent discoveries of potentially habitable exoplanets have ignited the
prospect of spectroscopic investigations of exoplanet surfaces and atmospheres
for signs of life. This chapter provides an overview of potential surface and
temporal exoplanet biosignatures, reviewing Earth analogues and proposed
applications based on observations and models. The vegetation red-edge (VRE)
remains the most well-studied surface biosignature. Extensions of the VRE,
spectral "edges" produced in part by photosynthetic or nonphotosynthetic
pigments, may likewise present potential evidence of life. Polarization
signatures have the capacity to discriminate between biotic and abiotic "edge"
features in the face of false positives from band-gap generating material.
Temporal biosignatures -- modulations in measurable quantities such as gas
abundances (e.g., CO2), surface features, or emission of light (e.g.,
fluorescence, bioluminescence) that can be directly linked to the actions of a
biosphere -- are in general less well studied than surface or gaseous
biosignatures. However, remote observations of Earth's biosphere nonetheless
provide proofs of concept for these techniques and are reviewed here. Surface
and temporal biosignatures provide complementary information to gaseous
biosignatures, and while likely more challenging to observe, would contribute
information inaccessible from study of the time-averaged atmospheric
composition alone.Comment: 26 pages, 9 figures, review to appear in Handbook of Exoplanets.
Fixed figure conversion error
The operation of two decarboxylases, transamination, and partitioning of C4 metabolic processes between mesophyll and bundle sheath cells allows light capture to be balanced for the maize C4 pathway.
The C4 photosynthesis carbon-concentrating mechanism in maize (Zea mays) has two CO2 delivery pathways to the bundle sheath (BS; via malate or aspartate), and rates of phosphoglyceric acid reduction, starch synthesis, and phosphoenolpyruvate regeneration also vary between BS and mesophyll (M) cells. The theoretical partitioning of ATP supply between M and BS cells was derived for these metabolic activities from simulated profiles of light penetration across a leaf, with a potential 3-fold difference in the fraction of ATP produced in the BS relative to M (from 0.29 to 0.96). A steady-state metabolic model was tested using varying light quality to differentially stimulate M or BS photosystems. CO2 uptake, ATP production rate (JATP; derived with a low oxygen/chlorophyll fluorescence method), and carbon isotope discrimination were measured on plants under a low light intensity, which is considered to affect C4 operating efficiency. The light quality treatments did not change the empirical ATP cost of gross CO2 assimilation (JATP/GA). Using the metabolic model, measured JATP/GA was compared with the predicted ATP demand as metabolic functions were varied between M and BS. Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in BS and M when light capture was varied under contrasting light qualities
Optimal allocation patterns and optimal seed mass of a perennial plant
We present a novel optimal allocation model for perennial plants, in which
assimilates are not allocated directly to vegetative or reproductive parts but
instead go first to a storage compartment from where they are then optimally
redistributed. We do not restrict considerations purely to periods favourable
for photosynthesis, as it was done in published models of perennial species,
but analyse the whole life period of a perennial plant. As a result, we obtain
the general scheme of perennial plant development, for which annual and
monocarpic strategies are special cases.
We not only re-derive predictions from several previous optimal allocation
models, but also obtain more information about plants' strategies during
transitions between favourable and unfavourable seasons. One of the model's
predictions is that a plant can begin to re-establish vegetative tissues from
storage, some time before the beginning of favourable conditions, which in turn
allows for better production potential when conditions become better. By means
of numerical examples we show that annual plants with single or multiple
reproduction periods, monocarps, evergreen perennials and polycarpic perennials
can be studied successfully with the help of our unified model.
Finally, we build a bridge between optimal allocation models and models
describing trade-offs between size and the number of seeds: a modelled plant
can control the distribution of not only allocated carbohydrates but also seed
size. We provide sufficient conditions for the optimality of producing the
smallest and largest seeds possible
Delving deeper: metabolic processes in the metalimnion of stratified lakes
Many lakes exhibit seasonal stratification, during which they develop strong thermal and chemical gradients. An expansion of depth-integrated monitoring programs has provided insight into the importance of organic carbon processing that occurs below the upper mixed layer. However, the chemical and physical drivers of metabolism and metabolic coupling remain unresolved, especially in the metalimnion. In this depth zone, sharp gradients in key resources such as light and temperature co-occur with dynamic physical conditions that influence metabolic processes directly and simultaneously hamper the accurate tracing of biological activity. We evaluated the drivers of metalimnetic metabolism and its associated uncertainty across 10 stratified lakes in Europe and North America. We hypothesized that the metalimnion would contribute highly to whole-lake functioning in clear oligotrophic lakes, and that metabolic rates would be highly variable in unstable polymictic lakes. Depth-integrated rates of gross primary production (GPP) and ecosystem respiration (ER) were modelled from diel dissolved oxygen curves using a Bayesian approach. Metabolic estimates were more uncertain below the epilimnion, but uncertainty was not consistently related to lake morphology or mixing regime. Metalimnetic rates exhibited high day-to-day variability in all trophic states, with the metalimnetic contribution to daily whole-lake GPP and ER ranging from 0% to 87% and<1% to 92%, respectively. Nonetheless, the metalimnion of low-nutrient lakes contributed strongly to whole-lake metabolism on average, driven by a col- linear combination of highlight, low surface-water phosphorous concentration and high metalimnetic volume. Consequently, a single-sensor approach does not necessarily reflect whole-ecosystem carbon dynamics in stratified lakes
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