Navegando por Autor "Araujo, Wagner L."

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In field-grown coffee trees source–sink manipulation alters photosynthetic rates, independently of carbon metabolism, via alterations in stomatal function
(New Phytologist, 2008-02-05) DaMatta, Fábio M.; Cunha, Roberto L.; Antunes, Werner C.; Martins, Samuel C. V.; Araujo, Wagner L.; Fernie, Alisdair R.; Moraes, Gustavo A. B. K.
Perturbations of the source–sink balances were performed in field-grown coffee (Coffea arabica) trees to investigate the possible role of carbohydrates in feedback regulation of photosynthesis. Four treatments were applied at the whole-plant level: (i) complete defruiting and maintenance of the full leaf area, (ii) the half crop load and full leaf area, (iii) the full crop load and full leaf area and (iv) the full crop load and half leaf area. Sampling and measurements were performed twice during the phase of dry matter accumulation of fruits. Gas exchange, chlorophyll a fluorescence, carbon isotope labelling and steady-state metabolite measurements were assessed in source leaves. The average rate of net photosynthetic rate (A) and stomatal conductance (g s) were larger (> 50%), and carbon isotope composition ratio was lower, in trees with a full crop load and half leaf area than in defruited trees, with individuals of the other two treatments showing intermediate values. However, differences in A seem unlikely to have been caused either by photochemical impairments or a direct end-product-mediated feedback down-regulation of photosynthesis. It is proposed that the decreased A in defruited coffee trees was independent of carbon metabolism and was rather directly related to a lower CO 2 availability coupled to lower gs.
Leveraging metabolomics for functional investigations in sequenced marine diatoms
(Trends in Plant Science, 2012-07) Fernie, Alisdair R.; Obata, Toshihiro; Allen, Andrew E.; Araujo, Wagner L.; Bowler, Chris
Recent years have witnessed the genomic decoding of a wide range of photosynthetic organisms from the model plant Arabidopsis thaliana and the complex genomes of important crop species to single-celled marine phytoplankton. The comparative sequencing of green, red and brown algae has provided considerable insight into a number of important questions concerning their evolution, physiology and metabolism. The combinatorial application of metabolomics has further deepened our understanding both of the function of individual genes and of metabolic processes. Here we discuss the power of utilising metabolomics in conjunction with sequencing data to gain greater insight into the metabolic hierarchies underpinning the function of individual organisms, using unicellular marine diatoms as a case study to exemplify the advantages of this approach.
Limitations to photosynthesis in coffee leaves from different canopy positions
(Plant Physiology and Biochemistry, 2008-05-24) Araujo, Wagner L.; Dias, Paulo C.; Moraes, Gustavo A.B.K.; Celin, Elaine F.; Cunha, Roberto L.; Barros, Raimundo S.; DaMatta, Fábio M.
Limitations to photosynthesis were explored in leaves from four canopy positions of field-grown, unshaded coffee (Coffea arabica L.), a tropical tree species classified as shade-obligatory. Overall, compared to shade (lower) leaves, sun (upper) leaves had higher net carbon assimilation rate (A) (4.5 against 2.0 μmol m−2 s−1 at most) associated with higher electron transport rate (due to a greater irradiance availability) but unrelated to stomatal and mesophyll conductances, which were similar regardless of leaf position. Neither physiological variable directly involved with photosynthetic carbon gain nor those involved with light capture were able to adjust themselves to match the capacity of the photosynthetic machinery to the light supply. We concluded that: (i) there was no major difference in photosynthetic capacity between sun and shade leaves; (ii) the intrinsic low A in coffee was greatly associated with remarkable low diffusive limitations rather than with biochemical or photochemical constraints; and (iii) morphological (e.g., variations in specific leaf area and leaf inclination) or anatomical plasticity should be of greater acclimative value than physiological plasticity as a mean of coffee leaves to respond to changing irradiance.
The mitochondrial thioredoxin system contributes to the metabolic responses under drought episodes in Arabidopsis
(Plant and Cell Physiology, 2019-01) Fonseca-Pereira, Paula da; Daloso, Danilo M.; Gago, Jorge; Silva, Franklin Magnum de Oliveira; Condori-Apfata, Jorge A.; Florez-Sarasa, Igor; Tohge, Takayuki; Reichheld, Jean-Philippe; Nunes-Nesi, Adriano; Fernie, Alisdair R.; Araujo, Wagner L.
Thioredoxins (Trxs) modulate metabolic responses during stress conditions; however, the mechanisms governing the responses of plants subjected to multiple drought events and the role of Trxs under these conditions are not well understood. Here we explored the significance of the mitochondrial Trx system in Arabidopsis following exposure to single and repeated drought events. We analyzed the previously characterized NADPH-dependent Trx reductase A and B double mutant (ntra ntrb) and two independent mitochondrial thioredoxin o1 (trxo1) mutant lines. Following similar reductions in relative water content (∼50%), Trx mutants subjected to two drought cycles displayed a significantly higher maximum quantum efficiency (Fv/Fm) and were less sensitive to drought than their wild-type counterparts and than all genotypes subjected to a single drought event. Trx mutant plants displayed a faster recovery after two cycles of drought, as observed by the higher accumulation of secondary metabolites and higher stomatal conductance. Our results indicate that plants exposed to multiple drought cycles are able to modulate their subsequent metabolic and physiological response, suggesting the occurrence of an exquisite acclimation in stressed Arabidopsis plants. Moreover, this differential acclimation involves the participation of a set of metabolic changes as well as redox poise alteration following stress recovery.
Morphological and physiological responses of two coffee progenies to soil water availability
(Journal of Plant Physiology, 2006-12-19) Dias, Paulo C.; Araujo, Wagner L.; Moraes, Gustavo A.B.K.; Barros, Raimundo S.; DaMatta, Fábio M.
Drought is a major environmental constraint affecting growth and production of coffee. The effects of water supply on growth, biomass allocation, water relations, and gas exchange in two coffee progenies representing drought-tolerant (Siriema) and drought-sensitive (Catucaí) genotypes were compared. They were grown in 12-L pots until 4-months old, when they were submitted to two watering treatments for 60 d: plants receiving either 100% transpired water (control plants) or a fraction (about 40%) of the amount of water transpired by control plants (drought-stressed plants). Under control conditions, Siriema grew faster than Catucaí. Regardless of the watering regimes and progenies, relative growth rate (RGR) was positively correlated both with net assimilation rate (NAR) and long-term water-use efficiency (WUE), but not with differences in biomass allocation. Both progenies responded to drought stress through (i) similar decreases in both RGR and NAR with marginal, if any, changes in allocation; (ii) decreases in leaf water potential, which occurred to a greater extent in Catucaí than in Siriema, even though they have showed similar abilities to adjust osmotically and elastically; (iii) similar reductions in net photosynthesis due mainly to nonstomatal factors; and (iv) decreases in transpiration rate coupled with increased long-term WUE. However, the lower transpiration rate and the higher long-term WUE as found in Siriema relative to Catucaí under control conditions persisted under drought conditions. Overall, the major differences between these progenies were largely associated with differences in plant water use, which was likely related to the improved water status of Siriema. The possible implications of selecting coffee genotypes for high WUE are discussed.
Unusual cyanobacterial TCA cycles: not broken just different
(Trends in Plant Science, 2012-09) Steinhauser, Dirk; Fernie, Alisdair R.; Araujo, Wagner L.
As a fundamental energy-conserving process common to all living organisms, respiration is responsible for the oxidation of respiratory substrates to drive ATP synthesis. Accordingly, it has long been accepted that a complete tricarboxylic acid (TCA) cycle is necessary for respiratory energy production. Cyanobacteria, similar to some other prokaryotes, appeared to have an incomplete TCA cycle because they lack the enzyme 2-oxoglutarate dehydrogenase (OGDH). However, it has recently been reported that the cycle can be completed by the action of two alternative enzymes. In this opinion article, we discuss the progress being made to elucidate the nature of the TCA cycles in cyanobacteria and plants and outline open questions concerning the functional significance of this unusual metabolic feature in a broader evolutionary context.