On electrostatic and Casimir force measurements between conducting surfaces in a sphere-plane configuration

We report on measurements of forces acting between two conducting surfaces in a spherical-plane configuration in the 35 nm-1 micrometer separation range. The measurements are obtained by performing electrostatic calibrations followed by a residual analysis after subtracting the electrostatic-dependent component. We find in all runs optimal fitting of the calibrations for exponents smaller than the one predicted by electrostatics for an ideal sphere-plane geometry. We also find that the external bias potential necessary to minimize the electrostatic contribution depends on the sphere-plane distance. In spite of these anomalies, by implementing a parametrixation-dependent subtraction of the electrostatic contribution we have found evidence for short-distance attractive forces of magnitude comparable to the expected Casimir-Lifshitz force. We finally discuss the relevance of our findings in the more general context of Casimir-Lifshitz force measurements, with particular regard to the critical issues of the electrical and geometrical characterization of the involved surfaces.Comment: 22 pages, 15 figure

Superimposed impacts of enhanced [CO2] and high temperature on the photosynthetic metabolism of C. arabica and C. canephora genotypes.

Summary: Coffee crop has been predicted to become threatened by future climate changes and global warming conditions. Yet, the long-term effects of elevated [CO2] on this plant remain to be fully elucidated. In this context, this work aims at linking coffee biochemical responses to environmental changes of [CO2] and temperature on genotypes from the two major producing species, using the photosynthetic metabolism as probe to evaluate the plant acclimation ability. Potted plants from C. arabica cv. IPR 108 and of C. canephora cv. Conilon Clone 153 were grown under environmental controlled conditions, either at 380 or 700 ?L CO2 L-1 air, for 1 year, without water, nutrient or root development restrictions. After that the temperature was gradually increased from 25/20 ºC (day/night) up to 42/34 ºC. The effects of elevated [CO2] and enhanced temperature on the photosynthetic structures were assessed through the characterization of the lipid components of chloroplast membranes, whereas the leaf metabolic performance was evaluated through the thylakoid electron transport rates (involving both photosystem (PS) I and II), and the activities of enzymes (ribulose 1,5-biphosphate carboxylase/oxygenase and ribulose 5-phosphate kinase), as well as through stable isotopes of C and N. The activities of respiratory enzymes (NADH-dependent malate dehydrogenase and pyruvate kinase) were also analyzed. The results pointed for a higher functional status along the experiment in the plants grown under elevated [CO2], with special relevance at 37 and 42ºC in IPR108. These results could be related to the qualitative changes of the membrane lipid matrix that might have helped to preserve suitable membrane fluidity for the membrane bound events (e.g., thylakoid electron transport). The PSs and enzyme data reflect an enhancement of the energetic metabolism (both photosynthesis and respiration), mostly, until 31 ºC for IPR108 and 37 ºC for CL153 at normal [CO2]. Yet, under enhanced [CO2] it was found an increase in the temperature (to 37 ºC) at which maximal values of some parameters in IPR108 (MDH, PSs activities, RuBisCO) were observed, concomitantly with the maintenance of high performance in other parameters when compared to the 380 plants. Under the highest temperature (42 ºC) the enzymes were the most sensitive point, displaying the strongest reductions, irrespective of genotype and [CO2] treatments. The temperature promoted changes in leaf ?13C, irrespective of genotype and [CO2], reflecting a decrease in WUE with heat. The changes in ?15N values may indicate different limitation steps of N assimilation, requiring further investigation. It was concluded that the coffee plants grown under elevated [CO2] apparently showed a better endurance to high temperatures, what is quite relevant in a context of predicted climate changes and global warming scenarios

Effect of high [CO2] and temperature on the photosynthetic enzymes and electron transport of Coffea Arabica L..

It is expected that future climate changes and global warming conditions will limit the coffee crop yields. However, the real effects of enhanced air [CO2] and temperature on this plant remain completely unknown. Therefore, this work studied the impact of such environmental changes on the photosynthetic machinery of Coffea arabica L. cv. Icatu. Plants were grown for 1 year under controlled conditions (temperature, RH, irradiance, photoperiod), at 380 or 700 ?L CO2 L-1 air, without nutrient, water and root space limitations, and then subjected to temperature increase (0.5ºC/day) to 42/34ºC. Thylakoid electron transport involving PSI and II, and enzyme activities (RuBisCO and RuB5PK) were assessed at 25/20ºC, 31/25ºC, 37/30ºC and 42/34ºC.The results showed a marginal impact until 37 ºC irrespective of [CO2] conditions, configuring a clear tolerance to supra-optimal temperatures. Also, a higher metabolic performance was observed in the plants under high [CO2]. Only at 42 ºC the tolerance limit was exceeded, as shown by significant impacts in all parameters, particularly in enzymes, but under elevated [CO2] a better performance was preserved regarding the photosystems functioning. Our findings showed that the elevated [CO2] allowed maintenance of higher metabolic activity and seemed to some extent mitigate the heat impact at the photosystems level, what is quite relevant in a context of predict global warming scenarios. This work was supported by Portuguese funds from Fundação para a Ciência e a Tecnologia, through the project PTDC/AGR-PRO/3386/2012

A glimpse of climate change impact on C. Arabica L. and C. Canephora Pierre ex A. Froehner physiology: the combined effects of enhanced growth CO2 and temperature.

Summary: The effective impact of climate changes on the coffee plant physiology, promoted by enhanced air [CO2] and global warming remain to be fully elucidated through biological studies. Therefore, this work aims at linking important coffee physiological responses to environmental changes of enhanced growth [CO2] and temperature on genotypes from the two major producing species. Potted plants from C. arabica cv. IPR 108 and of C. canephora cv. Conilon Clone 153 were grown under environmental controlled conditions, either at 380 or 700 ?L CO2 L-1 air, for 1 year, without water, nutrient or root development restrictions. After that the temperature was gradually increased from 25/20 ºC (day/night) up to 42/34 ºC. The long-term impacts of enhanced growth [CO2] and enhanced temperature on the photosynthetic functioning were assessed at 25/20 ºC, 31/25 ºC, 37/30 ºC and 42/34 ºC, through leaf gas exchanges (rates of net photosynthesis, Pn, stomatal conductance, gs, transpiration, Tr, and photosynthetic capacity, Amax), instantaneous water use efficiency (iWUE), fluorescence parameters (photochemical efficiency of the photosystem II under dark, Fv/Fm, and light, Fv?/Fm?, conditions, as well as the photochemical, qP, and non-photochemical, NPQ, quenchings, and quantum yield of the linear electron transport, ?e), photosynthetic pigments (chlorophyll and carotenoids) and some molecules with antioxidant role (ascorbate and ?-tocopherol). The results showed that enhanced [CO2] stimulates photosynthetic functioning, without negative down-regulation. Minor impacts were found in the photochemical performance until 37 ºC, but extensive impacts were shown at 42 ºC, especially in IPR108. Remarkable was the finding that enhanced [CO2] preserved a higher functional status (Pn, Amax, Fo, Fv/Fm) at high temperatures (37 and 42 ºC), what seems quite relevant under the predicted climate changes and global warming scenarios

Efeitos do aumento da temperatura e da [C02] atmosférica ao nível do funcionamento dos fotossistemas e transporte tilacoidal de elétrons em C. Arabica L. CV. Icatu

Resumo: Neste trabalho pretendeu-se estudar a extensão do impacto da temperatura no funcionamento dos fotossistemas (PS) I e II e do transporte tilacoidal de elétrons em C. arabica cv. lcatu e o possível efeito benéfico do aumento de [C0 2

Thylakoid lipids changes may account for photosynthetic acclimation ability of two coffea species subjected to heat.

Summary: Coffee is one of the world?s most traded agricultural products, and its production could be threatened by global warming. The aim of this work was to evaluate the effects of heat on photosynthetic activity and thylakoid membrane lipid dynamics, on genotypes of the two major coffee producing species. Potted plants from C. arabica L. cv. IPR108 and C. canephora Pierre Ex A. Froehner cv. Conilon Clone 153 were grown for 1 year under controlled conditions of temperature (25/20ºC, day/night), irradiance (650-800 ?mol m-2 s-1), RH (75%), photoperiod (12 h), and 380 ?L CO2 L-1. Thereafter, temperature was gradually raised to 42/34ºC (0.5ºC/ day), with a 7 days stabilization step at 31, 37 and 42ºC. Studies focused modifications of thylakoid lipid composition and photosynthetic performance. In CL153 photosynthetic capacity (Amax) was not affected until 42ºC (40% reduction). In IPR108 it was reduced 35 and 57% at 37ºC at 42ºC, respectively. Thylakoid electron transport rate for photosystems (PS) I and II increased (ca. 10-25%) up to 37ºC in both genotypes. At 42ºC only IPR108 presented depressed activities on PSII (15%) and PSI (18%). Under 37 and 42ºC, CL153 plants presented digalactosyldiacylglycerol (DGDG) (ca. 42%) and monogalactosyldiacylglycerol (MGDG) (28-34%) increases, while IPR108 showed higher MGDG at all temperatures. In CL153 less unsaturated DGDG and phosphatidylglycerol (PG) along with stable or increased DGDG/MGDG ratio, may have contributed to sustain thylakoid electron flow at 37ºC and even 42ºC. IPR108 displayed a strong PG rise at all temperatures, in accordance with enhanced PSs activity

Aumento da concentração de CO2 permite C. arabica remodelar a composição lipídica das membranas dos cloroplastos para aclimatar às altas temperaturas.

Entre as mudanças climáticas globais previstas, o aumento da temperatura ambiente é considerado uma das mais prejudiciais para o metabolismo das plantas. Esperam-se aumentos na temperatura do ar entre 0,3-1,7 ºC (melhor cenário) até 2,6-4,8 °C (pior cenário) até 2100, que serão acompanhados de um aumento na concentração de CO2([CO22L-1(ppm) (IPCC, 2014). É bem conhecido que as temperaturas supra-ótimas podem causar perturbações significativas no metabolismo, crescimento das plantas e processos reprodutivos, uma vez que as reações químicas são aceleradas, as ligações químicas enfraquecidas e a matriz lipídica das membranas tornam-se mais fluida. Além disso, extremos de temperatura podem causar desnaturação e agregação de proteínas, bem como a produção excessiva de espécies reativas de oxigênio e a inibição de processos de transcrição e de tradução (Larcher, 1995; Krishna, 2004). As membranas dos tilacóides são particularmente sensíveis às temperaturas elevadas, pelo que danos na fase fotoquímica da fotossíntese estão entre os primeiros indicadores de sensibilidade a tal stress. As membranas dos tilacóides consistem principalmente de galactolípidos [monogalactosildiacilglicerol (MGDG) e digalactosildiacilglicerol (DGDG)], que representam 70-80% da matriz lipídica dos tilacóides. Fosfolípidos e sulfoquinovosildiacilglicerol (SQDG) completam as classes presentes (Joyardet al., 1980; Nishihara et al., 1980). Alterações na composição dos ácidos gordos das membranas plasmáticas estão entre as estratégias usadas pelas plantas para lidar com o stresse térmico (Campos et al., 2013; Chen et al., 2006; Partelli et al., 2011). Em genótipos de C. arábica a temperaturas até 42 ºC foi recentemente observado que o aumento na [CO2] melhora o funcionamento do aparato fotossintético e promove o reforço dos sistemas de defesa, envolvendo, por exemplo, compostos antioxidantes enzimáticos e não enzimáticos, proteínas de choque térmico e pigmentos de proteção (Rodrigues et al., 2016; Martins et al., 2016). No entanto, permanece por esclarecer se o aumento da [CO2] permite uma melhor dinâmica e remodelação lipídica das membranas dos cloroplastos que permita manter uma fluidez adequada às suas funções sob altas temperaturas. Assim, no presente trabalho foram estudadas as classes de lípidos ao nível da membrana dos cloroplastos em plantas de C arábica cv. IPR 108 com 1,5 anos de idade, cultivadas em vasos de 28 L, mantidas emcâmaras de crescimento (FitoclimaEHHF 10000, ARALAB, Portugal) durante 1 ano em condições ambientais controladas de temperatura (25/20 ºC, dia/noite), irradiância (ca. 650-800 mol m-2s-1), humidade relativa (75%), fotoperíodo (12 h) e 380 ou 700 ppm de [CO2], sem restrições de água, nutrientes ou espaço para desenvolvimento radicular. Após esse período, a temperatura foi gradualmente aumentada de 25/20 ºC até 42/34 ºC, a uma taxa de 0,5 ºC dia-1, com uma estabilização de 7 dias nas temperaturas 31/25, 37/30 e 42/34 ºC para efectuar as análises em folhas recém-maduras. As classes de lípidos foram separadas por meio de cromatografia em camada fina utilizando placas de sílica gel G60 (Merck) e os seus ácidos gordos analisados por cromatografia gas-líquido (GC-FID, Varian, CP-3380, USA), como descrito e adaptado para plantas de café (Campos et al., 2003; Partelliet al., 2011)