Search

SUMMARY: The importance of the alternative donation of electrons to the ubiquinol pool via the electron‐transfer flavoprotein/electron‐transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex has been demonstrated. However, the functional significance of this pathway during seed development and germination remains to be elucidated. To assess the function of this pathway, we performed a detailed metabolic and transcriptomic analysis of Arabidopsis mutants to test the molecular consequences of a dysfunctional ETF/ETFQO pathway. We demonstrate that the disruption of this pathway compromises seed germination in the absence of an external carbon source and also impacts seed size and yield. Total protein and storage protein content is reduced in dry seeds, whilst sucrose levels remain invariant. Seeds of ETFQO and related mutants were also characterized by an altered fatty acid composition. During seed development, lower levels of fatty acids and proteins accumulated in the etfqo‐1 mutant as well as in mutants in the alternative electron donors isovaleryl‐CoA dehydrogenase (ivdh‐1) and d‐2‐hydroxyglutarate dehydrogenase (d2hgdh1‐2). Furthermore, the content of several amino acids was increased in etfqo‐1 mutants during seed development, indicating that these mutants are not using such amino acids as alternative energy source for respiration. Transcriptome analysis revealed alterations in the expression levels of several genes involved in energy and hormonal metabolism. Our findings demonstrated that the alternative pathway of respiration mediated by the ETF/ETFQO complex affects seed germination and development by directly adjusting carbon storage during seed filling. These results indicate a role for the pathway in the normal plant life cycle to complement its previously defined roles in the response to abiotic stress. Significance Statement: The importance of the alternative donation of electrons to the ubiquinol pool via the electron‐transfer flavoprotein/electron‐transfer flavoprotein:ubiquinone oxidoreductase (ETF/ETFQO) complex during normal seed development and germination is presented. Our results provide compelling evidence for a pivotal role of the alternative ETF/ETFQO respiration pathway in the normal life cycle of a plant in addition to its previously defined roles in response the to abiotic stress. [ABSTRACT FROM AUTHOR]

Drought is considered the main environmental factor limiting productivity in eucalyptus plantations in Brazil. However, recent studies have reported that exposure to water deficit conditions enables plants to respond to subsequent stresses. Thus, this study investigates the ecophysiological acclimatization of eucalyptus clones submitted to recurrent water deficit cycles. Eucalyptus seedlings were submitted to three recurrent water deficit cycles and anatomical, morphological and physiological changes were analyzed. The results were: (1) Eucalyptus seedlings responded to water deficits by directing carbohydrates to root and stem growth; (2) Size and number of stomata were reduced; (3) Stomatal conductance decreased which allowed the plants to reduce water losses through transpiration, increasing instantaneous water use efficiency; (4) The relationship between gas exchanges and available water contents allowed the seedlings to uptake the retained soil water at higher tensions; and, (5) Physiological recovery from subsequent water deficits became faster. As a result of these changes, the eucalyptus seedlings recovered from the same degree of water stress more rapidly. [ABSTRACT FROM AUTHOR]

Cyanobacteria often store excessive organic carbon in the form of glycogen and extracellular polysaccharides (EPS) under higher light intensities. However, their partition pattern and relation has long been overlooked. In this study, the partition and possible relationship between extracellular EPS and intracellular glycogen under different light intensities (4, 40, 80 µE m-2s-1) were explored; with the exception of glycogen and EPS, the intracellular total sugar, water soluble sugar and sucrose of two species cyanobacteria, Microcoleus vaginatus FACHB 896 and Nostoc sp. FACHB 892 isolated from biological soil crusts, were also synchronously analyzed. The results showed that, the production of EPS (including released polysaccharides, RPS and capsular polysaccharides, CPS) in the two species all began from the exponential phase, and increased with the increasing light intensities, but glycogen content did not increase until the increment of light intensities was enough strong. Even though, their competition was obvious at the optimal light intensity. In pattern, even at the exponential phase, the two species only partitioned a little organic carbon in glycogen, more than 10 times in EPS. In EPS, CPS generally accounted for higher proportion than RPS, but the increase of RPS was much higher than that of CPS with the increasing light intensity and culture time. These results suggested that the partition of extracellular EPS and intracellular glycogen was closely related to acclimation to light intensity. [ABSTRACT FROM AUTHOR]

Lysine (Lys) connects the mitochondrial electron transport chain to amino acid catabolism and the tricarboxylic acid cycle. However, our understanding of how a deficiency in Lys biosynthesis impacts plant metabolism and growth remains limited. Here, we used a previously characterized Arabidopsis mutant (dapat) with reduced activity of the Lys biosynthesis enzyme L,L-diaminopimelate aminotransferase to investigate the physiological and metabolic impacts of impaired Lys biosynthesis. Despite displaying similar stomatal conductance and internal CO2concentration, we observed reduced photosynthesis and growth in the dapat mutant. Surprisingly, whilst we did not find differences in dark respiration between genotypes, a lower storage and consumption of starch and sugars was observed in dapat plants. We found higher protein turnover but no differences in total amino acids during a diurnal cycle in dapat plants. Transcriptional and two-dimensional (isoelectric focalization/SDS-PAGE) proteome analyses revealed alterations in the abundance of several transcripts and proteins associated with photosynthesis and photorespiration coupled with a high glycine/serine ratio and increased levels of stress-responsive amino acids. Taken together, our findings demonstrate that biochemical alterations rather than stomatal limitations are responsible for the decreased photosynthesis and growth of the dapat mutant, which we hypothesize mimics stress conditions associated with impairments in the Lys biosynthesis pathway. [ABSTRACT FROM AUTHOR]

Controlled hot rolling is performed on low carbon Q&P steel and is subsequently followed by a direct Q&P (DQP) treatment and a separate Q&P treatment (SQP). Two different levels of strain viz. 0.51 and 1.1 are accomplished in the thermomechanical controlled process (TMCP) prior to the Q&P treatment. The microstructures of the steels processed through both the DQP and SQP methods with different thickness reductions, contain primarily small lath packets with fine martensite laths and thin films of inter-lath austenite. Comparatively higher martensite volume fractions and fine lath packets is noticed in the DQP method. Tendency of higher retained austenite fraction is observed in the SQP method. Presence of a high fractions of high angle grain boundaries (HAGB) in the martensite laths indicates a fully recrystallized prior austenite grains in both steels. In general, prior thermo-mechanical treatment improves the partition kinetics which is supported by the high value of calculated carbon content of the austenite, C ϒ , in the DQP steels. Combination of TMCP and Q&P process has resulted in remarkable increase in strength with adequate ductility compared to a simple Q&P treatment alone. Maximum strength of about 1398 MPa with a total elongation of 14% is achieved in the 1.1DQP steel. The study suggests that performing a TMCP prior to Q&P promotes grain refinement and formation of high fractions of HAGBs that are beneficial to improve the tensile properties. [ABSTRACT FROM AUTHOR]

Key message: The carbon flow balance is shifted to starch rather than oil accumulation during benzoin seed development stage (80-120 DAF) and thereby lipid deposition speed slows down. Abstract: Benzoin [ Styrax tonkinensis (Pierre) Craib ex Hartwich] is a woody oilseed species with potential value as a biofuel feedstock. However, the continuous drop in seed crude fat concentration during maturation had remained unexplained until it was investigated in this study. Seed filling began 60 days after flowering (DAF), when the hexose-to-sucrose ratio dropped, correlating with substantial morphological changes in kernels. Oil accumulated 20 days earlier than starch, as the concentrations of free fatty acid (50-70 DAF) and diacylglycerols (50-80 DAF) increased rapidly. Fatty acid synthesis slowed between 80 and 120 days, correlating with a sharp increase in the speed of starch deposition, while triacylglycerol accumulation and the profile of fatty acids remained stable. Phosphoglucose isomerase (PGI), pyruvate dehydrogenase complex (PDHC), and malate dehydrogenase (MDH) activities dropped progressively together with acetyl coenzyme carboxylase (ACCase) after 70 DAF before the reserve storage priority shifted from fatty acids to starch. PGI, PDHC, MDH, ACCase, and diglyceride acyltransferase (DAGT) activities rose again at 120 DAF, after which the speed of fatty acid accumulation increased, correlating with a 10-day lag phase in starch accumulation. High glucose 6-phosphate dehydrogenase (G6PDH) activity was observed during oil deposition. Soluble protein continued accumulating as protease activity decreased during benzoin seed development, while the total amylase activity rose twice between 30 and 70 DAF before the ADP-glucose pyrophosphorylase activity and starch content soared high simultaneously after 70 DAF. The collective results suggest that carbon partitioning between starch and lipid accumulation occurs during benzoin kernel development and is responsible for a reduction in the rate at which total fatty acids accumulate between 80 and 120 DAF. [ABSTRACT FROM AUTHOR]

Abstract: It is widely established that nutritional nitrogen deprivation increases lipid accumulation but severely decreases growth rate in microalgae. To understand the regulatory branch points that determine the partitioning of carbon among its potential sinks, we analyzed metabolite and transcript levels of central carbon metabolic pathways and determined the average fluxes and quantum requirements for the synthesis of protein, carbohydrates and fatty acid in the diatom Phaeodactylum tricornutum. Under nitrate-starved conditions, the carbon fluxes into all major sinks decrease sharply; the largest decrease was into proteins and smallest was into lipids. This reduction of carbon flux into lipids together with a significantly lower growth rate is responsible for lower overall FA productivities implying that nitrogen starvation is not a bioenergetically feasible strategy for increasing biodiesel production. The reduction in these fluxes was accompanied by an 18-fold increase in α-ketoglutarate (AKG), 3-fold increase in NADPH/NADP+, and sharp decreases in glutamate (GLU) and glutamine (GLN) levels. Additionally, the mRNA level of acetyl-CoA carboxylase and two type II diacylglycerol-acyltransferases were increased. Partial suppression of nitrate reductase by tungstate resulted in similar trends at lower levels as for nitrate starvation. These results reveal that the GS/GOGAT pathway is the main regulation site for nitrate dependent control of carbon partitioning between protein and lipid biosynthesis, while the AKG/GL(N/U) metabolite ratio is a transcriptional signal, possibly related to redox poise of intermediates in the photosynthetic electron transport system. [Copyright &y& Elsevier]