Antônio Celso Magalhães

Chilling stress leads to increased cell membrane rigidity in roots of coffee (Coffea arabica L.) seedlings

Tropical and sub-tropical higher plant species show marked growth inhibition when exposed to chilling temperatures. In root tip segments of coffee seedlings which were subjected for 6 days to temperatures of 10, 15, 20 and 25 degrees C, in darkness, we have detected an increased amount of malondialdehyde formed in the 10 degrees C treatment, accompanied by higher electrolyte leakage. The electron paramagnetic resonance (EPR) technique and the fatty acid spin probes 5-, 12- and 16-doxylstearic acid were used to assess cellular membrane fluidity. At the depth of the 5th and 16th carbon atom of the alkyl chains the nitroxide radical detected more rigid membranes in seedlings subjected to 10 degrees C compared with 15 and 25 degrees C. At the C-12 position of the chains the probe showed very restricted motion and was insensitive to chilling induced membrane alterations. EPR parameters for intact tissues and microsome preparations from root tips showed that the fluidity was essentially the same when evaluated at C-5 and C-16 positions of the chains, and was considerably more fluid for microsomal membranes in the region of the C-12 position of the bilayers. The rotational motion of the nitroxide at C-16 position of the chains experienced a phase transition at about 15 degrees C. The calculated energy barriers for reorientational motion of the probe 16-doxylstearic acid were higher at temperatures of 5-15 degrees C than in the interval of 15-25 degrees C, suggesting that below the phase transition the membrane lipids assume a more ordered and compacted array. Membrane rigidity induced by chilling was interpreted as due to lipid peroxidation that could have been facilitated by higher density of peroxidizable chains below the membrane phase transition.

CHILLING-INDUCED CHANGES IN MEMBRANE FLUIDITY AND ANTIOXIDANT ENZYME ACTIVITIES IN COFFEA ARABICA L. ROOTS

Exposure of coffee to low temperatures caused growth inhibition, changes in metabolic rates, and membrane alterations. Root tissue exposed to 10 °C evolved significantly lower rates of metabolic heat compared with controls grown at 25 °C, and the values were closely associated with the observed root growth inhibition. Electron paramagnetic resonance spectra of intact tissues showed that the spin probe 5-doxylstearic acid was capable to intercalate within the cellular membrane lipids. Indeed, at the depth of the 5th carbon atoms of the alkyl chains, the nitroxide radical detected more rigid membranes in seedlings exposed to 10 °C compared with 25 °C treated samples. Ascorbate peroxidase and catalase activities did not show appreciable changes under chilling conditions, while guaiacol peroxidase activity increased 55 % compared to the control. On the other hand, glutathione reductase activity decreased, in parallel to a significant decline in the capacity to reduce triphenyl-tetrazolium. Our results showed a marked correlation between lipid peroxidation and root tissue damage, which seemed to be associated with increased membrane rigidity.

Caffeine metabolism in Coffea arabica and other species of coffee

Abstract High performance liquid chromatography has been used to measure the quantities of caffeine, theobromine, and theophylline in aqueous extracts of endosperm from immature and mature fruits of Coffea arabica and six other species of Coffea . Caffeine was the alkaloid present in largest amounts and, with one exception, in concentrations that were broadly similar in immature and mature fruit. The highest concentrations of caffeine were found in C. canephora at 35.1 and 24.5 mg g −1 , respectively, in immature and mature endosperm. The lowest concentrations were in C. bengalensis , where caffeine was not detected in extracts from mature fruit. [8- 3 H]Caffeine was metabolised relatively slowly by immature endosperm of C. arabica and C. canephora . In contrast, C. dewevrei , C. eugenioides , C. stenophylla , C. salvatrix and C. bengalensis all appeared to metabolise [8- 3 H]caffeine much more rapidly, as the percentage recovery of the applied label was much lower and there was more extensive incorporation of radioactivity into theobromine, theophylline, 3-methylxanthine and two unidentified polar metabolites. The endogenous caffeine concentrations and the metabolism data indicate that there may be marked differences in the rate of turnover of caffeine in the various species of Coffea . Potential sources of material for the production of naturally decaffeinated coffee are discussed.

The Phenomenon of Photoinhibition of Photosynthesis and Its Importance in Reforestation

Photoinhibition, defined as the inhibition of photosynthesis caused by excessive radiance, affects field production to a great extent. This phenomenon is particularly relevant in reforestation practices, when one deals with forests of rapid growth such asEucalyptus. The imposition of additional stress factors during exposure to high radiance increases the potential for photoinhibitory effects, so the inhibition of photosynthesis indicates that the plant is submitted to stressful conditions. Photoinhibition can be reversible, playing a protective role for the photosynthetic systems, but it can also reflect damage that has already occurred in the photosynthetic apparatus, being irreversible in this case. In this review, we present the physiological and molecular mechanisms of photoinhibition and discuss the interaction between light and other stress factors and its effects on plants destined for reforestation. In addition, the present work analyzes some of the features and strategies that help plants avoid or restrict the occurrence of photoinhibition. For instance, pigments and enzymes which naturally occur in plants can prevent photoinhibition, while preadaptation to nonideal conditions can enhance tolerance to a certain stress factor. Most of these morphological, metabolic, and biochemical mechanisms of defense are related to the dissipation of excessive energy such as heat. Understanding these mechanisms can help improve cultivation procedures, avoid the plants’ death, and increase productivity in the field.

The effect of chilling on the photosynthetic activity in coffee (Coffea arabica L.) seedlings: The protective action of chloroplastid pigments

A especie Coffea arabica e considerada sensivel as baixas temperaturas, podendo ser afetada em todo o seu ciclo. A injuria pelo frio (temperaturas baixas acima de zero) se caracteriza, principalmente, pela inibicao do processo fotossintetico. Este trabalho teve como objetivo avaliar a participacao dos pigmentos fotossinteticos na tolerância de plântulas de cafeeiro (C. arabica L.) a temperatura de resfriamento. A avaliacao da atividade fotossintetica foi feita atraves da emissao de fluorescencia da clorofila a a temperatura ambiente (25 oC) in vivo e in situ, usando um fluorimetro portatil. O conteudo dos pigmentos foi obtido a partir da extracao com acetona 80 % e a peroxidacao lipidica estimada a partir das medidas do conteudo de MDA em extratos do tecido foliar. Os resultados indicaram uma reducao generalizada na eficiencia quântica do PSII quando as plântulas foram mantidas no escuro. A reducao ocorreu tanto nas plântulas submetidas ao tratamento de resfriamento, quanto no material controle. Isso demonstra que nao apenas a temperatura de resfriamento estaria atuando como causa dessas alteracoes na atividade do PSII. E provavel que tenha ocorrido um esgotamento das reservas do tecido, com a taxa respiratoria excedendo a fotossintetica, ja que essa era nula, uma vez que a energia de excitacao esteve comprometida pela permanencia das plântulas no escuro. A eficiencia na captura, transferencia e utilizacao da energia luminosa em reacoes fotoquimicas no PSII, requer uma sequencia de eventos fotoquimicos, bioquimicos e biofisicos intimamente dependentes da integridade estrutural do aparelho fotossintetico. Sendo que essa eficiencia se mostrou mais dependente da acao protetora dos pigmentos cloroplastidicos do que propriamente da concentracao desses.

Photosynthetic O2 evolution in maize inbreds and their hybrids can be differentiated by open photoacoustic cell technique

Abstract Photosynthetic efficiency is considered one of the traits potentially suitable to differentiate hybrids from their inbred lines. Previous evaluations concerning photosynthetic efficiencies of maize (Zea mays L.) plants in the field have shown inconsistent and contradictory data. In this work, we attempted to study photosynthetic O2 evolution through photoacoustic spectroscopy in intact undetached leaves of dark-adapted seedlings of inbreds and their hybrids. The results indicate that photosynthetic efficiencies of inbreds and hybrids can be differentiated by photoacoustic measurements of oxygen evolution, providing a parameter that might prove useful in evaluating plant genotypes.

Changes in nitrate reductase activity during development of soybean leaf

Summary The in vivo and in vitro nitrate reductase activities during the ontogeny of the first leaf showed maximum values at the time of maximum rate of leaf expansion. During this phase the changes of the enzyme activity depend on the level of endogenous nitrate in the tissues, which accumulated preferentialy in young leaves. It was shown that the in vitro nitrate reductase instability increases as leaf age progresses. Inclusion of 3 % Casein in the enzyme extraction medium significantly improved enzyme activity suggesting that caScin could effect the balance between some activating and inactivating component associated with the protein molecule. When nitrate was supplied via the petioles of excised leaves it could be demonstrated that old leaves accumulated less nitrate than young ones. In addition it was shown that the nitrate concentration in the leaf alter the relation between in vivo and in vitro nitrate reductase activities.

Microcalorimetric evaluation of metabolic heat rates in coffee (Coffea arabica L.) roots of seedlings subjected to chilling stress

In numerous tropical and sub-tropical plant species, such as coffee, exposure to low temperatures can cause extensive tissue damage, the seedlings being particularly sensitive to chilling stress. This condition usually induces changes in the metabolic rates, and there are indications that this process can be evaluated by monitoring heat evolution by microcalorimetry. We studied the responses of coffee seedlings to chilling stress by measuring root growth and metabolic heat rates in apical root segments of coffee seedlings exposed for 6 days to temperatures ranging from 5 to 25°C. The metabolic heat rates were measured in a heat conduction calorimeter. Root growth was progressively hindered as the seedlings were exposed to temperatures below 15°C; low temperature-induced growth inhibition was closely correlated with the lowering of metabolic heat rates. An Arrhenius plot of metabolic heat rate revealed a break in the line at 15°C, suggesting the occurrence of a metabolic transition at this temperature. The microcalorimetric technique provides a sensitive, non-invasive method for evaluating plant growth responses to chilling stress.

Efeito da redução da superfície foliar sôbre o desenvolvimento de cafeeiros

The influence of reducing 25, 50 and 75 percent of the leaf arca on the growth of the coffee plant was studied. For this purpose the area of each one of all the individual leaves of one and half year old coffee plants was reduced by cutting off part of the leaf blade in those proportions. The Net Assimilation Rate (NAR) and the Relative Growth Rate (RGR) were determined. The reduction of the leaf area decreased the dry weight and reduced the leaf growth rate in 32.6, 42.7 and 54.0% and 6.4, 44.6 and 54,1% respectively with the cutting off of 25, 50 and 75% of leaf area. With the reduction of leaf area, the RGR decreased, while the NAR increased.

Nitrate reduction in young coffee trees grown under different levels of light and nitrogen

The effect of levels of light and nitrogen on the activity of the enzyme nitrate reductase and its relationship with the availability of sugars and nitrate was studied in leaves of coffee plants (Coffea arabica L. cv. Catual). Ten month old plants were grown on pots containing a mixture of soil and compost, and were kept at full or 50% sunlight. Half of the plants of each light treatment received nitrogen supply. The results showed that the activity of nitrate reductase was higher on plants supplied with nitrogen at both light treatments. For the same nitrogen level, plants grown under full sunlight presented lower nitrate reductase activity, higher nitrate and sugars concentrations, and higher transpiration rates than plants kept at 50% sunlight. These results indicate that the lower nitrate reductase activity of plants grown under full sunlight was apparently not due to limitations of available nitrate and sugars to supply the energy necessary for nitrate reduction.