Daylength variation affects growth, photosynthesis, leaf metabolism, partitioning, and metabolic fluxes.

Daylength, a seasonal and latitudinal variable, exerts a substantial impact on plant growth. However, the relationship between daylength and growth is nonproportional, suggesting the existence of adaptive mechanisms. Thus, our study aimed to comprehensively investigate the adaptive strategies employed by plants in response to daylength variation.

Integrated flux and pool size analysis in plant central metabolism reveals unique roles of glycine and serine during photorespiration.

Photorespiration is an essential process juxtaposed between plant carbon and nitrogen metabolism that responds to dynamic environments. Photorespiration recycles inhibitory intermediates arising from oxygenation reactions catalysed by Rubisco back into the C cycle, but it is unclear what proportions of its nitrogen-containing intermediates (glycine and serine) are exported into other metabolisms in vivo and how these pool sizes affect net CO gas exchange during photorespiratory transients. Here, to address this uncertainty, we measured rates of amino acid export from photorespiration using isotopically non-stationary metabolic flux analysis.

Phosphoglucoisomerase Is an Important Regulatory Enzyme in Partitioning Carbon out of the Calvin-Benson Cycle.

Phosphoglucoisomerase (PGI) isomerizes fructose 6-phosphate (F6P) and glucose 6-phosphate (G6P) in starch and sucrose biosynthesis. Both plastidic and cytosolic isoforms are found in plant leaves. Using recombinant enzymes and isolated chloroplasts, we have characterized the plastidic and cytosolic isoforms of PGI.

Transcriptional Regulation of the Glucose-6-Phosphate/Phosphate Translocator 2 Is Related to Carbon Exchange Across the Chloroplast Envelope.

The exchange of reduced carbon across the inner chloroplast envelope has a large impact on photosynthesis and growth. Under steady-state conditions it is thought that glucose 6-phosphate (G6P) does not cross the chloroplast membrane. However, growth at high CO, or disruption of starch metabolism can result in the gene for a G6P/P translocator to be expressed presumably allowing G6P exchange across the chloroplast envelope.

Time of day and network reprogramming during drought induced CAM photosynthesis in Sedum album.

Plants with facultative crassulacean acid metabolism (CAM) maximize performance through utilizing C3 or C4 photosynthesis under ideal conditions while temporally switching to CAM under water stress (drought). While genome-scale analyses of constitutive CAM plants suggest that time of day networks are shifted, or phased to the evening compared to C3, little is known for how the shift from C3 to CAM networks is modulated in drought induced CAM. Here we generate a draft genome for the drought-induced CAM-cycling species Sedum album.

A Cytosolic Bypass and G6P Shunt in Plants Lacking Peroxisomal Hydroxypyruvate Reductase.

The oxygenation of ribulose 1,5-bisphosphate by Rubisco is the first step in photorespiration and reduces the efficiency of photosynthesis in C plants. Our recent data indicate that mutants in photorespiration have increased rates of photosynthetic cyclic electron flow around photosystem I. We investigated mutant lines lacking peroxisomal hydroxypyruvate reductase to determine if there are connections between 2-phosphoglycolate accumulation and cyclic electron flow in Arabidopsis ().

Isoprene Acts as a Signaling Molecule in Gene Networks Important for Stress Responses and Plant Growth.

Isoprene synthase converts dimethylallyl diphosphate to isoprene and appears to be necessary and sufficient to allow plants to emit isoprene at significant rates. Isoprene can protect plants from abiotic stress but is not produced naturally by all plants; for example, Arabidopsis () and tobacco () do not produce isoprene. It is typically present at very low concentrations, suggesting a role as a signaling molecule; however, its exact physiological role and mechanism of action are not fully understood.

Triose phosphate use limitation of photosynthesis: short-term and long-term effects.

The triose phosphate use limitation was studied using long-term and short term changes in capacity. The TPU limitation caused increased proton motive force; long-term TPU limitation additionally reduced other photosynthetic components. Photosynthetic responses to CO2 can be interpreted primarily as being limited by the amount or activity of Rubisco or the capacity for ribulose bisphosphate regeneration, but at high rates of photosynthesis a third response is often seen.

The glucose 6-phosphate shunt around the Calvin-Benson cycle.

It is just over 60 years since a cycle for the regeneration of the CO2-acceptor used in photosynthesis was proposed. In this opinion paper, we revisit the origins of the Calvin-Benson cycle that occurred at the time that the hexose monophosphate shunt, now called the pentose phosphate pathway, was being worked out. Eventually the pentose phosphate pathway was separated into two branches, an oxidative branch and a non-oxidative branch.

The relationship between leaf area growth and biomass accumulation in Arabidopsis thaliana.

Leaf area growth determines the light interception capacity of a crop and is often used as a surrogate for plant growth in high-throughput phenotyping systems. The relationship between leaf area growth and growth in terms of mass will depend on how carbon is partitioned among new leaf area, leaf mass, root mass, reproduction, and respiration. A model of leaf area growth in terms of photosynthetic rate and carbon partitioning to different plant organs was developed and tested with Arabidopsis thaliana L.

The arc mutants of Arabidopsis with fewer large chloroplasts have a lower mesophyll conductance.

Photosynthetic cells of most land plant lineages have numerous small chloroplasts even though most algae, and even the early diverging land plant group the hornworts, tend to have one or a few large chloroplasts. One constraint that small chloroplasts could improve is the resistance to CO2 diffusion from the atmosphere to the chloroplast stroma. We examined the mesophyll conductance (inverse of the diffusion resistance) of mutant Arabidopsis thaliana plants with one or only a few large chloroplasts per cell.

Evolution of the Phosphoenolpyruvate Carboxylase Protein Kinase Family in C3 and C4 Flaveria spp.

The key enzyme for C photosynthesis, Phosphoenolpyruvate Carboxylase (PEPC), evolved from nonphotosynthetic PEPC found in C ancestors. In all plants, PEPC is phosphorylated by Phosphoenolpyruvate Carboxylase Protein Kinase (PPCK). However, differences in the phosphorylation pattern exist among plants with these photosynthetic types, and it is still not clear if they are due to interspecies differences or depend on photosynthetic type.

Isopentenyl diphosphate and dimethylallyl diphosphate/isopentenyl diphosphate ratio measured with recombinant isopentenyl diphosphate isomerase and isoprene synthase.

Isopentenyl diphosphate (IDP) and its isomer dimethylallyl diphosphate (DMADP) are building units for all isoprenoids; thus, intracellular pool sizes of IDP and DMADP play important roles in living organisms. Several methods have been used to quantify the amount of DMADP or the combined amount of IDP plus DMADP, but measuring the DMADP/IDP ratio has been difficult. In this study, a method was developed to measure the ratio of DMADP/IDP.

Measuring dimethylallyl diphosphate available for isoprene synthesis.

Dimethylallyl diphosphate (DMADP) is a central metabolite in isoprenoid metabolism, but it is difficult to measure. Three different methods for measuring DMADP are compared, and a new method based on the conversion of DMADP to isoprene using recombinant isoprene synthase is introduced. Mass spectrometry is reliable but does not distinguish between DMADP and isopentenyl diphosphate.

Engineering starch accumulation by manipulation of phosphate metabolism of starch.

A new understanding of leaf starch degradation has emerged in the last 10 years. It has been shown that starch phosphorylation and dephosphorylation are critical components of this process. Glucan, water dikinase (GWD) (and phosphoglucan, water dikinase) adds phosphate to starch, and phosphoglucan phosphatase (SEX4) removes these phosphates.

The interactions between the circadian clock and primary metabolism.

Primary metabolism in plants is tightly regulated by environmental factors such as light and nutrient availability at multiple levels. The circadian clock is a self-sustained endogenous oscillator that enables organisms to predict daily and seasonal changes. The regulation of primary metabolism by the circadian clock has been proposed to explain the importance of circadian rhythms in plant growth and survival.

Increasing the energy density of vegetative tissues by diverting carbon from starch to oil biosynthesis in transgenic Arabidopsis.

Increasing the energy density of biomass by engineering the accumulation of triacylglycerols (TAGs) in vegetative tissues is synergistic with efforts to produce biofuels by conversion of lignocellulosic biomass. Typically, TAG accumulates in developing seeds, and little is known about the regulatory mechanisms and control factors preventing oil biosynthesis in vegetative tissues in most plants. Here, we engineered Arabidopsis thaliana to ectopically overproduce the transcription factor WRINKLED1 (WRI1) involved in the regulation of seed oil biosynthesis.

The role of transitory starch in C(3), CAM, and C(4) metabolism and opportunities for engineering leaf starch accumulation.

Essentially all plants store starch in their leaves during the day and break it down the following night. This transitory starch accumulation acts as an overflow mechanism when the sucrose synthesis capacity is limiting, and transitory starch also acts as a carbon store to provide sugar at night. Transitory starch breakdown can occur by either of two pathways; significant progress has been made in understanding these pathways in C(3) plants.

A putative phosphatase, LSF1, is required for normal starch turnover in Arabidopsis leaves.

A putative phosphatase, LSF1 (for LIKE SEX4; previously PTPKIS2), is closely related in sequence and structure to STARCH-EXCESS4 (SEX4), an enzyme necessary for the removal of phosphate groups from starch polymers during starch degradation in Arabidopsis (Arabidopsis thaliana) leaves at night. We show that LSF1 is also required for starch degradation: lsf1 mutants, like sex4 mutants, have substantially more starch in their leaves than wild-type plants throughout the diurnal cycle. LSF1 is chloroplastic and is located on the surface of starch granules.

Carbon balance and circadian regulation of hydrolytic and phosphorolytic breakdown of transitory starch.

Transitory starch is formed in chloroplasts during the day and broken down at night. Transitory starch degradation could be regulated by light, circadian rhythms, or carbon balance. To test the role of these potential regulators, starch breakdown rates and metabolites were measured in bean (Phaseolus vulgaris) and Arabidopsis (Arabidopsis thaliana) plants.

Cellular and organ level localization of maltose in maltose-excess Arabidopsis mutants.

Maltose is the predominant form of carbon exported from the chloroplast at night. Plants that lack either the chloroplast maltose transporter or disproportionating enzyme 2 (DPE2, EC 2.4.

beta-Maltose is the metabolically active anomer of maltose during transitory starch degradation.

Maltose is the major form of carbon exported from the chloroplast at night as a result of transitory starch breakdown. Maltose exists as an alpha- or beta-anomer. We developed an enzymatic technique for distinguishing between the two anomers of maltose and tested the accuracy and specificity of this technique using beta-maltose liberated from maltoheptose by beta-amylase.

Maltose is the major form of carbon exported from the chloroplast at night.

Transitory starch is formed in chloroplasts during the day and broken down at night. We investigated carbon export from chloroplasts resulting from transitory-starch breakdown. Starch-filled chloroplasts from spinach ( Spinacia oleracea L.