Ricardo Ferraz de Oliveira

Photosynthesis and water relations of well-watered orange plants as affected by winter and summer conditions

The aim of this study was to evaluate how the summer and winter conditions affect the photosynthesis and water relations of well-watered orange trees, considering the diurnal changes in leaf gas exchange, chlorophyll (Chl) fluorescence, and leaf water potential (Ψ) of potted-plants growing in a subtropical climate. The diurnal pattern of photosynthesis in young citrus trees was not significantly affected by the environmental changes when compared the summer and winter seasons. However, citrus plants showed higher photosynthetic performance in summer, when plants fixed 2.9 times more CO2 during the diurnal period than in the winter season. Curiously, the winter conditions were more favorable to photosynthesis of citrus plants, when considering the air temperature (< 29 °C), leaf-to-air vapor pressure difference (< 2.4 kPa) and photon flux density (maximum values near light saturation) during the diurnal period. Therefore, low night temperature was the main environmental element changing the photosynthetic performance and water relations of well-watered plants during winter. Lower whole-plant hydraulic conductance, lower shoot hydration and lower stomatal conductance were noticed during winter when compared to the summer season. In winter, higher ratio between the apparent electron transport rate and leaf CO2 assimilation was verified in afternoon, indicating reduction in electron use efficiency by photosynthesis. The high radiation loading in the summer season did not impair the citrus photochemistry, being photoprotective mechanisms active. Such mechanisms were related to increases in the heat dissipation of excessive light energy at the PSII level and to other metabolic processes consuming electrons, which impede the citrus photoinhibition under high light conditions.

Early photosynthetic responses of sweet orange plants infected with Xylella fastidiosa

Abstract Photosynthetic processes of sweet orange plants [Citrus sinensis (L.) Osbeck cv. Pera] infected with Xylella fastidiosa were investigated. Simultaneous measurements of leaf gas exchanges and chlorophyll a fluorescence were taken in healthy and infected leaves before development of symptoms. The photosynthetic oxygen evolution response to different light intensities and curves of photosynthesis induction were carried out in leaf discs extracted from the same leaves used for gas exchange measurements. Infected plants showed decreased CO2 assimilation, transpiration and stomatal conductance. No differences between healthy and infected intact leaves regarding chlorophyll a fluorescence parameters were observed, except for the potential quantum yield of photosystem II which was higher in infected plants. Values of photosynthetic oxygen evolution, effective quantum yield of photosystem II, apparent electron transport rate, and photochemical fluorescence quenching were higher in healthy leaf discs than in infected ones. Our results suggest that low photosynthetic rates of non-symptomatically sweet orange leaves infected with X. fastidiosa were caused by low stomatal conductance, biochemical alterations of photosynthetic machinery and increase in alternative electron sinks.

Photosynthetic responses of tropical tree species from different successional groups under contrasting irradiance conditions

This study evaluated the photosynthetic responses of seven tropical trees of different successional groups under contrasting irradiance conditions, taking into account changes in gas exchange and chlorophyll a fluorescence. Although early successional species have shown higher values of CO2 assimilation (A) and transpiration (E), there was not a defined pattern of the daily gas exchange responses to high irradiance (FSL) among evaluated species. Cariniana legalis (Mart.) Kuntze (late secondary) and Astronium graveolens Jacq. (early secondary) exhibited larger reductions in daily-integrated CO2 assimilation (DIA) when transferred from medium light (ML) to FSL. On the other hand, the pioneer species Guazuma ulmifolia Lam. had significant DIA increase when exposed to FSL. The pioneers Croton spp. trended to show a DIA decrease around 19%, while Cytharexyllum myrianthum Cham. (pioneer) and Rhamnidium elaeocarpum Reiss. (early secondary) trended to increase DIA when transferred to FSL. Under this condition, all species showed dynamic photoinhibition, except for C. legalis that presented chronic photoinhibition of photosynthesis. Considering daily photosynthetic processes, our results supported the hypothesis of more flexible responses of early successional species (pioneer and early secondary species). The principal component analysis indicated that the photochemical parameters effective quantum efficiency of photosystem II and apparent electron transport rate were more suitable to separate the successional groups under ML condition, whereas A and E play a major role to this task under FSL condition.

Efeito da aplicação de piraclostrobina na taxa fotossintética, respiração, atividade da enzima nitrato redutase e produtividade de grãos de soja

With the aim to evaluate the effect of the pyraclostrobin application on physiological and phenometric variables in soybean crop, a field experiment was carried from November 2005 to May 2006. Evaluations of photosynthesis and respiration were taken, as well as nitrate reductase activity, 1000 seeds mass and soybean productivity. The statistical design was complete randomized blocks with three treatments (T 1 : no fungicide application; T 2 : two applications of pyraclostrobin and T 3 : two applications of tebuconazole - triazol) and four replications. The pyraclostrobin application raised the photosynthesis rate. The leaf nitrate reductase activity just raised after 15 days from first application of pyraclostrobin. Plants treated with strobilurin (T2) showed increase of 7 and 8% in 1000 seeds mass and 1080 and 468 kg ha -1 in the soybean productivity when compared to T 1 and T 3 , respectively. The results indicate that pyraclostrobin (strobilurin) application affects carbon and nitrogen assimilation in soybean crop that is reflected on the grain yield.

High temperature effects on the response of photosynthesis to light in sweet orange plants infected with Xylella fastidiosa

fluorescence to the increase in light intensity were evaluated at 35oC and 45oC in bothhealthy and infected leaf discs. The increase in temperature affected the photosynthetic apparatus of both healthy and infectedplants, although infected plants showed higher photochemical sensitivity at the higher temperature (e.g. in the potential quantumefficiency of photosystem II, maximum and basal fluorescence yield, and in the relation between variable and basal fluorescenceyield). This higher sensitivity of infected plants was not reflected in the overall photosynthetic reaction, since photosyntheticoxygen evolution values did not vary at 45oC. Healthy and infected plants showed differences in photosynthetic oxygen evolutionbut displayed similar effective quantum efficiency of photosystem II as well as apparent electron transport rates at 35oC. Theseresults suggest that the limitations in photosynthesis observed on the infected plants might arise through impaired biochemicalreactions.

Temporal dynamics of stomatal conductance of plants under water deficit: can homeostasis be improved by more complex dynamics?

In this study we hypothesized that chaotic or complex behavior of stomatal conductance could improve plant homeostasis after water deficit. Stomatal conductance of sunflower and sugar beet leaves was measured in plants grown either daily irrigation or under water deficit using an infrared gas analyzer. All measurements were performed under controlled environmental conditions. In order to measure a consistent time series, data were scored with time intervals of 20s during 6h. Lyapunov exponents, fractal dimensions, KS entropy and relative LZ complexity were calculated. Stomatal conductance in both irrigated and non-irrigated plants was chaotic-like. Plants under water deficit showed a trend to a more complex behaviour, mainly in sunflower that showed better homeostasis than in sugar beet. Some biological implications are discussed.

Temperature response of photosynthesis and its interaction with light intensity in sweet orange leaf discs under non-photorespiratory condition

This study aimed to evaluate the response of photosynthesis (A), given by photosynthetic O 2 evolution, to increasing temperature from 25 to 50oC in sweet orange (Citrus sinensis (L.) Osbeck) leaf discs under non-photorespiring conditions. In order to evaluate the response of gross photosynthesis to temperature and the balance between photosynthetic and respiratory activities, respiration (R d ) rates were also measured, i.e. the O 2 uptake in each temperature. In addition, light response curves of photosynthesis were performed by varying the photosynthetic photon flux density (PPFD) from 0 to 1160 mol m -2 s -1 at 25 and 40 o C. The highest A values were observed at 35 and 40 o C, whereas the highest R d values were noticed at 50oC. A higher relationship A/R d was found at 30 and 35oC, suggesting an optimum temperature of 35oC when considering the balance between photosynthesis and respiration under non-photorespiring condition. Overall, heat effects on plant metabolism were more evident when evaluating the relationship A/ R d . In light response curves, higher A values were also found at 40oC under PPFD higher than 300 mol m -2 s -1 . Light saturation point of photosynthesis was increased at 40oC, without significant change of quantum efficiency under low PPFD. Respiration was also enhanced at 40oC, and as a consequence, the light compensation point increased. The better photosynthetic performance at 35-40oC was supported by higher photochemical efficiency in both light and temperature response curves. The temperature-dependence of photosynthesis was affected by growth temperature, i.e. a high air temperature during plant growth is a probable factor leading to a higher photosynthetic tolerance to heat stress.

Photosynthetic responses of young cashew plants to varying environmental conditions

O objetivo deste trabalho foi caracterizar as respostas das trocas gasosas de plantas jovens de cajueiro a densidade de fluxo de fotons fotossintetico (DFFF), temperatura, deficit de pressao de vapor (DPV) e concentracao interna de CO 2 (C i ), sob condicoes controladas. Cursos diarios das trocas gasosas e de variaveis de fluorescencia da clorofila a foram obtidos sob condicoes naturais. A taxa de assimilacao de CO 2 maxima foi de cerca de 13 mmol m -2 s -1 , com saturacao pela luz em torno de 1.000 mmol m -2 s -1 . As temperaturas das folhas entre 25 o C e 35 o C corresponderam a faixa otima para a fotossintese. Os estomatos mostraram-se sensiveis ao CO 2 e se fecharam com aumentos de C i . Aumentos do DPV exerceram pequeno efeito sobre a taxa de assimilacao de CO 2 , com uma pequena diminuicao acima de 2,5 kPa. Os estomatos, no entanto, foram fortemente afetados pelo DPV, com fechamento gradativo acima de 1,5 kPa. As condutâncias estomaticas, reduzidas em altos DPVs, foram eficientes em restringir as perdas de agua pela transpiracao e demonstraram adaptacao da especie a ambientes secos. Sob irradiância natural, a taxa de assimilacao de CO 2 apresentou saturacao no inicio da manha, variando posteriormente com as variacoes da DFFF. Decrescimos transientes da razao F v /F m foram registrados em torno de 11h, o que indica a ocorrencia de fotoinibicao. Decrescimos da eficiencia de captura da energia de excitacao, decrescimos da eficiencia efetiva do fotossistema II e aumentos da extincao nao-fotoquimica foram consistentes com a ocorrencia de fotoprotecao sob irradiância excessiva.

Photochemical heat-shock response in common bean leaves as affected by previous water deficit

The heat sensitivity of photochemical processes was evaluated in the common bean (Phaseolus vulgaris) cultivars A222, A320, and Carioca grown under well-watered conditions during the entire plant cycle (control treatment) or subjected to a temporal moderate water deficit at the preflowering stage (PWD). The responses of chlorophyll fluorescence to temperature were evaluated in leaf discs excised from control and PWD plants seven days after the complete recovery of plant shoot hydration. Heat treatment was done in the dark (5 min) at the ambient CO2 concentration. Chlorophyll fluorescence was assessed under both dark and light conditions at 25, 35, and 45°C. In the dark, a decline of the potential quantum efficiency of photosystem II (PSII) and an increase in minimum chlorophyll fluorescence were observed in all genotypes at 45°C, but these responses were affected by PWD. In the light, the apparent electron transport rate and the effective quantum efficiency of PSII were reduced by heat stress (45°C), but no change due to PWD was demonstrated. Interestingly, only the A222 cultivar subjected to PWD showed a significant increase in nonphotochemical fluorescence quenching at 45°C. The common bean cultivars had different photochemical sensitivities to heat stress altered by a previous water deficit period. Increased thermal tolerance due to PWD was genotype-dependent and associated with an increase in potential quantum efficiency of PSII at high temperature. Under such conditions, the genotype responsive to PWD treatment enhanced its protective capacity against excessive light energy via increased nonphotochemical quenching.

A new concept for insect damage evaluation based on plant physiological variables

The objective of this study was to determine the damage levels caused by Orthezia praelonga Douglas, 1891 and Leucoptera coffeella (Guérin-Mèneville 1842), on rangpur lime and Obatã coffee leaves, respectively. Measurements were based on a new concept for the evaluation of the following plant physiological parameters: photosynthesis, stomatal conductance, leaf temperature and transpiration, and internal concentration of CO2 (by infrared analyzer). A negative correlation between infestation level and photosynthesis was found, where the negative inflexion point of the curve was considered as a reference for damage levels. The control level for O. praelonga is below the 7-13% limit for damaged leaf area (40 to 70 scales per leaf), while for L. coffeella it is below the 26-36% limit for the same variable. Photosynthesis provided the best correlation for this type of analysis.