Papers by salvador nogues
Plant Cell and Environment, 2004
The effects of chilling under low light (9/7 ∞ ∞ ∞ ∞ C, 100 m m m m mol m ----2 s ----1
The effects of 24-epibrassinolide (EBR) spray application on gas-exchange, chlorophyll¯uorescence... more The effects of 24-epibrassinolide (EBR) spray application on gas-exchange, chlorophyll¯uorescence characteristics, Rubisco activity, and carbohydrate metabolism were investigated in cucumber (Cucumis sativus L. cv. Jinchun No. 3) plants grown in a greenhouse. EBR signi®cantly increased the light-saturated net CO 2 assimilation rate (A sat ) from 3 h to 7d after spraying, with 0.1 mg l ±1 EBR proving most effective. Increased A sat in EBR-treated leaves was accompanied by increases in the maximum carboxylation rate of Rubisco (V c,max ) and in the maximum rate of RuBP regeneration (J max ). EBR-treated leaves also had a higher quantum yield of PSII electron transport (f PSII ) than the controls, which was mainly due to a signi®cant increase in the photochemical quenching (q P ), with no change in the ef®ciency of energy capture by open PSII reaction centres (F ¢ v /F ¢ m ). EBR did not in¯uence photorespiration. In addition, signi®cant increases in the initial activity of Rubisco and in the sucrose, soluble sugars, and starch contents were observed followed by substantial increases in sucrose phosphate synthase (SPS), sucrose synthase (SS), and acid invertase (AI) activities after EBR treatment. It was concluded that EBR increases the capacity of CO 2 assimilation in the Calvin cycle, which was mainly attributed to an increase in the initial activity of Rubisco. Abbreviations, AI, acid invertase; A sat, light-saturated net CO 2 assimilation; BRs, brassinosteroids; EBR, 24-epibrassinolide; F v /F m , the maximal photochemical ef®ciency of PSII; F ¢ v /F ¢ m , the ef®ciency of excitation energy capture by open PSII reaction centres; J max , maximum potential rate of electron transport contributed to RuBP regeneration; l, stomatal limitation; f PSII , relative quantum ef®ciency of PSII photochemistry; q P , photochemical quenching; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase; RuBP, ribulose-1,5-bisphosphate; SPS, sucrose phosphate synthase; SS, sucrose synthase; V c, max , maximum carboxylation rate of Rubisco.
Journal of Experimental Botany, 2006
Very little is known about the primary carbon metabolism of the high mountain plant Ranunculus gl... more Very little is known about the primary carbon metabolism of the high mountain plant Ranunculus glacialis. It is a species with C 3 photosynthesis, but with exceptionally high malate content in its leaves, the biological significance of which remains unclear. 13 C/ 12 C-isotope ratio mass spectrometry (IRMS) and 13 C-nuclear magnetic resonance (NMR) labelling were used to study the carbon metabolism of R. glacialis, paying special attention to respiration. Although leaf dark respiration was high, the temperature response had a Q 10 of 2, and the respiratory quotient (CO 2 produced divided by O 2 consumed) was nearly 1, indicating that the respiratory pool is comprised of carbohydrates. Malate, which may be a large carbon substrate, was not respired. However, when CO 2 fixed by photosynthesis was labelled, little labelling of the CO 2 subsequently respired in the dark was detected, indicating that: (i) most of the carbon recently assimilated during photosynthesis is not respired in the dark; and (ii) the carbon used for respiration originates from (unlabelled) reserves. This is the first demonstration of such a low metabolic coupling of assimilated and respired carbon in leaves. The biological significance of the uncoupling between assimilation and respiration is discussed. Abbreviations: d 13 C, carbon isotope composition; D 13 C, carbon isotope discrimination; ETR, electron transport rate; IRMS, isotope ratio mass spectrometry; NADP-MDH, NADP-malate dehydrogenase; NMR, nuclear magnetic resonance; PEPcase, phosphoenolpyruvate-carboxylase; PPFD, photosynthetic active photon flux density; Q 10 , proportional changes in respiration per 10 8C rise in temperature; RQ, respiratory quotient.
Plant Physiology, 2004
The origin of the carbon atoms in the CO 2 respired by French bean (Phaseolus vulgaris) leaves in... more The origin of the carbon atoms in the CO 2 respired by French bean (Phaseolus vulgaris) leaves in the dark has been studied using 13 C/ 12 C isotopes as tracers. The stable isotope labeling was achieved through a technical device that uses an open gas-exchange system coupled online to an elemental analyzer and linked to an isotope ratio mass spectrometer. The isotopic analysis of the CO 2 respired in the dark after a light period revealed that the CO 2 was labeled, but the labeling level decreased progressively as the dark period increased. The pattern of disappearance depended on the amount of carbon fixed during the labeling and indicated that there were several pools of respiratory metabolites with distinct turnover rates. We demonstrate that the carbon recently assimilated during photosynthesis accounts for less than 50% of the carbon in the CO 2 lost by dark respiration and that the proportion is not influenced by leaf starvation in darkness before the labeling. Therefore, most of the carbon released by dark respiration after illumination does not come from new photosynthates. fax 33-1-69157238.
Rapid Communications in Mass Spectrometry, 2005
Discrimination against 13C during photosynthesis is a well-characterised phenomenon. It leaves be... more Discrimination against 13C during photosynthesis is a well-characterised phenomenon. It leaves behind distinct signatures in organic matter of plants and in the atmosphere. The former is depleted in 13C, the latter is enriched during periods of preponderant photosynthetic activity of terrestrial ecosystems. The intra-annual cycle and latitudinal gradient in atmospheric 13C resulting from photosynthetic and respiratory activities of terrestrial plants have been exploited for the reconstruction of sources and sinks through deconvolution by inverse modelling. Here, we compile evidence for widespread post-photosynthetic fractionation that further modifies the isotopic signatures of individual plant organs and consequently leads to consistent differences in delta13C between plant organs. Leaves were on average 0.96 per thousand and 1.91 per thousand more depleted than roots and woody stems, respectively. This phenomenon is relevant if the isotopic signature of CO2-exchange fluxes at the ecosystem level is used for the reconstruction of individual sources and sinks. It may also modify the parameterization of inverse modelling approaches if it leads to different isotopic signatures of organic matter with different residence times within the ecosystems and to a respiratory contribution to the average difference between the isotopic composition of plant organic matter and the atmosphere. We discuss the main hypotheses that can explain the observed inter-organ differences in delta13C.
Plant Physiology, 2003
The carbon isotope composition (␦ 13 C) of CO 2 produced in darkness by intact French bean (Phase... more The carbon isotope composition (␦ 13 C) of CO 2 produced in darkness by intact French bean (Phaseolus vulgaris) leaves was investigated for different leaf temperatures and during dark periods of increasing length. The ␦ 13 C of CO 2 linearly decreased when temperature increased, from Ϫ19‰ at 10°C to Ϫ24‰ at 35°C. It also progressively decreased from Ϫ21‰ to Ϫ30‰ when leaves were maintained in continuous darkness for several days. Under normal conditions (temperature not exceeding 30°C and normal dark period), the evolved CO 2 was enriched in 13 C compared with carbohydrates, the most 13 C-enriched metabolites. However, at the end of a long dark period (carbohydrate starvation), CO 2 was depleted in 13 C even when compared with the composition of total organic matter. In the two types of experiment, the variations of ␦ 13 C were linearly related to those of the respiratory quotient. This strongly suggests that the variation of ␦ 13 C is the direct consequence of a substrate switch that may occur to feed respiration; carbohydrate oxidation producing 13 C-enriched CO 2 and -oxidation of fatty acids producing 13 C-depleted CO 2 when compared with total organic matter (Ϫ27.5‰). These results are consistent with the assumption that the ␦ 13 C of dark respired CO 2 is determined by the relative contributions of the two major decarboxylation processes that occur in darkness: pyruvate dehydrogenase activity and the Krebs cycle. ; fax 33-1-69157238.
The effects of ultraviolet-B (UV-B) radiation on stomatal conductance (g s ) in pea (Pisum sativu... more The effects of ultraviolet-B (UV-B) radiation on stomatal conductance (g s ) in pea (Pisum sativum L.), commelina (Commelina communis L.), and oilseed rape (Brassica napus L.) plants were investigated. Plants were grown in a greenhouse either with three different high ratios of UV-B to photosynthetically active radiation or with no UV-B radiation. Pea plants grown in the highest UV-B radiation (0.63 W m ؊2 ) exhibited a substantial decrease of adaxial and abaxial g s (approximately 80% and 40%, respectively). With growth in 0.30 W m ؊2 of UV-B adaxial g s was decreased by 23%, with no effect on abaxial g s , and lower UV-B irradiance of 0.21 W m ؊2 had no effect on either surface. Although abaxial g s increased when leaves were turned over in control plants,
Plant Physiology, 1999
The effects of ultraviolet-B (UV-B) radiation on stomatal conductance (g s ) in pea (Pisum sativu... more The effects of ultraviolet-B (UV-B) radiation on stomatal conductance (g s ) in pea (Pisum sativum L.), commelina (Commelina communis L.), and oilseed rape (Brassica napus L.) plants were investigated. Plants were grown in a greenhouse either with three different high ratios of UV-B to photosynthetically active radiation or with no UV-B radiation. Pea plants grown in the highest UV-B radiation (0.63 W m ؊2 ) exhibited a substantial decrease of adaxial and abaxial g s (approximately 80% and 40%, respectively). With growth in 0.30 W m ؊2 of UV-B adaxial g s was decreased by 23%, with no effect on abaxial g s , and lower UV-B irradiance of 0.21 W m ؊2 had no effect on either surface. Although abaxial g s increased when leaves were turned over in control plants,
New Phytologist, 2002
The effects are reported here of inoculation with the soil-borne pathogen Fusarium oxysporum f. s... more The effects are reported here of inoculation with the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici race 1 (FOL-1) on the photosynthetic capacity of tomato plants ( Lycopersicon esculentum cv. Roma).
Two slow-growing plant species (Chamaerops humilis, L. and Cycas revoluta Thunb.) were exposed to... more Two slow-growing plant species (Chamaerops humilis, L. and Cycas revoluta Thunb.) were exposed to elevated CO 2 conditions over a 20-month period in order to study the CO 2 effect on growth, photosynthetic capacity and leaf carbon (C) management. The ambient isotopic 13 C/ 12 C composition (d 13 C) of the greenhouse module corresponding to elevated CO 2 (800 lmol mol À1 CO 2 ) conditions was changed from d 13 C ca. À12.8 AE 0.3% to ca. À19.2 AE 0.2%. Exposure of these plants to elevated CO 2 enhanced dry mass (DM) by 82% and 152% in Chamerops and Cycas, respectively, mainly as a consequence of increases in plant level photosynthetic rates. However, analyses of A-C i curve parameters revealed that elevated CO 2 diminished leaf photosynthetic rates of Chamaerops whereas in Cycas, no photosynthetic acclimation was detected. The fact that Chamaerops plants had a lower DM increase, together with a longer leaf C residence time and a diminished capacity to respire recently fixed C, suggests that this species was unable to increase C sink strength. Furthermore, the consequent C source/sink imbalance in Chamaerops might have induced the downregulation of Rubisco. Cycas plants were capable of avoiding photosynthetic downregulation due to a greater ability to increase C sink strength, as was confirmed by DM values, and 12 C-enriched CO 2 labeling data. Cycas developed the ability to respire a larger proportion of recently fixed C and to reallocate the recently fixed C away from leaves to other plant tissues. These findings suggest that leaf C management is a key factor in the responsiveness of slow-growing plants to future CO 2 scenarios.
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Papers by salvador nogues