Photosynthetic model for citrus cultivar Huangguogan / Modelo fotossintético para cultivar cítrico Huangguogan

Grafting is an effective measure to improve the photosynthetic rate of citrus. The light responses of photosynthesis in leaves of two-year old grafted Huangguogan (citrus cultivar Huangguogan), Huanggougan / Trifoliate (HG/PT), Huanggougan / Tangerine (HG/CR), and Huanggougan / Ziyang Xiangcheng (HG/CJ) were studied using the LI-COR 6400 portable photosynthesis system. Light-response curves and photosynthetic parameters were analyzed and fitted using the rectangular hyperbola model (RHM), the exponential model (EM), the non rectangular hyperbola model (NRHM), and the modified rectangular hyperbola model (MRHM). The results showed that: (1) Grafting can change the photosynthetic characteristics of Huangguogan, and the value of photosynthesis rate of HG/CJ is the greatest; (2) The light-response curves of net photosynthetic rate (PN), the light compensation point (LCP), and the dark respiration rate (RD) were well fitted using the above four models. The modified rectangular hyperbola was the best model in fitting the data; the nonrectangular hyperbola model was the second, and the rectangular hyperbola model was the poorest one.(AU)

O enxerto é uma medida eficaz para melhorar a taxa fotossintética de citros. As respostas leves da fotossíntese em folhas de Huangguogan (cultivar de citros Huangguogan), Huanggougan / Trifoliate (HG / PT), Huanggougan / Tangerine (HG / CR) e Huanggougan / Ziyang Xiangcheng (HG / CJ) foram estudadas usando o sistema de fotossíntese portátil LI-COR 6400.Curvas de resposta à luz e parâmetros fotossintéticos foram analisados e ajustados usando o modelo de hipérbole retangular (RHM), o modelo exponencial (EM), o modelo de hipérbole não retangular (NRHM) e o modelo de hipérbole retangular modificado (MRHM). Os resultados mostraram que: (1) O enxerto pode mudar as características fotossintéticas de Huangguogan, e o valor da taxa de fotossíntese de HG / CJ é o maior; (2) As curvas de resposta à luz da taxa fotossintética líquida (PN), do ponto de compensação de luz (LCP) e da taxa de respiração escura (RD) foram bem ajustadas usando os quatro modelos acima. A hipérbole retangular modificada foi o melhor modelo na adaptação dos dados; o modelo de hipérbole não-retangular foi o segundo, e o modelo de hipérbole retangular foi o mais pobre.(AU)

Photosynthetic model for citrus cultivar Huangguogan / Modelo fotossintético para cultivar cítrico Huangguogan

Grafting is an effective measure to improve the photosynthetic rate of citrus. The light responses of photosynthesis in leaves of two-year old grafted Huangguogan (citrus cultivar Huangguogan), Huanggougan / Trifoliate (HG/PT), Huanggougan / Tangerine (HG/CR), and Huanggougan / Ziyang Xiangcheng (HG/CJ) were studied using the LI-COR 6400 portable photosynthesis system. Light-response curves and photosynthetic parameters were analyzed and fitted using the rectangular hyperbola model (RHM), the exponential model (EM), the non rectangular hyperbola model (NRHM), and the modified rectangular hyperbola model (MRHM). The results showed that: (1) Grafting can change the photosynthetic characteristics of Huangguogan, and the value of photosynthesis rate of HG/CJ is the greatest; (2) The light-response curves of net photosynthetic rate (PN), the light compensation point (LCP), and the dark respiration rate (RD) were well fitted using the above four models. The modified rectangular hyperbola was the best model in fitting the data; the nonrectangular hyperbola model was the second, and the rectangular hyperbola model was the poorest one.

O enxerto é uma medida eficaz para melhorar a taxa fotossintética de citros. As respostas leves da fotossíntese em folhas de Huangguogan (cultivar de citros Huangguogan), Huanggougan / Trifoliate (HG / PT), Huanggougan / Tangerine (HG / CR) e Huanggougan / Ziyang Xiangcheng (HG / CJ) foram estudadas usando o sistema de fotossíntese portátil LI-COR 6400.Curvas de resposta à luz e parâmetros fotossintéticos foram analisados e ajustados usando o modelo de hipérbole retangular (RHM), o modelo exponencial (EM), o modelo de hipérbole não retangular (NRHM) e o modelo de hipérbole retangular modificado (MRHM). Os resultados mostraram que: (1) O enxerto pode mudar as características fotossintéticas de Huangguogan, e o valor da taxa de fotossíntese de HG / CJ é o maior; (2) As curvas de resposta à luz da taxa fotossintética líquida (PN), do ponto de compensação de luz (LCP) e da taxa de respiração escura (RD) foram bem ajustadas usando os quatro modelos acima. A hipérbole retangular modificada foi o melhor modelo na adaptação dos dados; o modelo de hipérbole não-retangular foi o segundo, e o modelo de hipérbole retangular foi o mais pobre.

Short-term UV-B exposure induces metabolic and anatomical changes in peel of harvested lemons contributing in fruit protection against green mold.

UV-B radiation (UVBR) is a small fraction of the solar spectrum from 280 to 315nm. UVBR produces photomorphogenic acclimation responses in plants, modulating their cellular structure and physiology. Here, changes in the peel of harvested lemons after short time exposure to UVBR were analyzed and its potential effects against fungal infection were studied. In the flavedo, UVBR treatment induced variations in the respiratory profiles and increased the phenolic compound contents. Final products of the flavonoid pathway (flavones, flavonols and anthocyanins) increased more markedly than their precursors (flavanones and dihydroflavonols). The increased accumulation of soluble phenolics in the flavedo of treated lemons is associated with the high antioxidant activity found in the flavedo of these samples. Supporting the biochemical determinations, anatomical observations showed abundant intravacuolar deposits of phenolic compounds and an increase in the cell wall thickness in UVBR-treated samples. Metabolic and anatomical modifications associated to UVBR improved natural defenses against Penicillium digitatum, the causal agent of green mold disease. Our results suggest that mature postharvest lemons exposed to the artificial radiation showed phenotypic plasticity, allowing an acclimation response to UVBR which confers fruit resistance to pathogens. Thus, combination of UVBR with other treatments could represent an important improvement to control postharvest diseases on citrus.

Continuous, high-resolution biospeckle imaging reveals a discrete zone of activity at the root apex that responds to contact with obstacles.

BACKGROUND AND AIMS: Shining a laser onto biological material produces light speckles termed biospeckles. Patterns of biospeckle activity reflect changes in cell biochemistry, developmental processes and responses to the environment. The aim of this work was to develop methods to investigate the biospeckle activity in roots and to characterize the distribution of its intensity and response to thigmostimuli. METHODS: Biospeckle activity in roots of Zea mays, and also Jatropha curcas and Citrus limonia, was imaged live and in situ using a portable laser and a digital microscope with a spatial resolution of 10 µm per pixel and the ability to capture images every 0.080 s. A procedure incorporating a Fujii algorithm, image restoration using median and Gaussian filters, image segmentation using maximum-entropy threshold methods and the extraction of features using a tracing algorithm followed by spline fitting were developed to obtain quantitative information from images of biospeckle activity. A wavelet transform algorithm was used for spectral decomposition of biospeckle activity and generalized additive models were used to attribute statistical significance to changes in patterns of biospeckle activity. KEY RESULTS: The intensity of biospeckle activity was greatest close to the root apex. Higher frequencies (3-6 Hz) contributed most to the total intensity of biospeckle activity. When a root encountered an obstacle, the intensity of biospeckle activity decreased abruptly throughout the root system. The response became attenuated with repeated thigmostimuli. CONCLUSIONS: The data suggest that at least one component of root biospeckle activity resulted from a biological process, which is located in the zone of cell division and responds to thigmostimuli. However, neither individual cell division events nor root elongation is likely to be responsible for the patterns of biospeckle activity.

Variability of 137Cs and 40K soil-to-fruit transfer factor in tropical lemon trees during the fruit development period.

In this investigation we evaluate the soil uptake of (137)Cs and (40)K by tropical plants and their consequent translocation to fruits, by calculating the soil-to-fruit transfer factors defined as F(v) = [concentration of radionuclide in fruit (Bq kg(-1) dry mass)/concentration of radionuclide in soil (Bq kg(-1) dry mass in upper 20 cm)]. In order to obtain F(v) values, the accumulation of these radionuclides in fruits of lemon trees (Citrus limon B.) during the fruit growth was measured. A mathematical model was calibrated from the experimental data allowing simulating the incorporation process of these radionuclides by fruits. Although the fruit incorporates a lot more potassium than cesium, both radionuclides present similar absorption patterns during the entire growth period. F(v) ranged from 0.54 to 1.02 for (40)K and from 0.02 to 0.06 for (137)Cs. Maximum F(v) values are reached at the initial time of fruit growth and decrease as the fruit develops, being lowest at the maturation period. As a result of applying the model a decreasing exponential function is derived for F(v) as time increases. The agreement between the theoretical approach and the experimental values is satisfactory.

Solar and supplemental UV-B radiation effects in lemon peel UV-B-absorbing compound content-seasonal variations.

Effects of solar and supplemental UV-B radiation on UV-B-absorbing compounds and malondialdehyde (MDA) accumulations in the peel of lemons collected in summer and winter were analyzed. UV-B-absorbing compounds were higher in flavedo than in albedo tissue in both seasons; however, the highest values were observed in summer. These compounds were also higher in outer than in inner flavedo surface. Lemons were categorized as sun-, semisun- and shaded-lemon according to localization inside the tree canopy. Depending on-tree localization UV-B-absorbing compounds were higher in flavedo of sun-lemon than in semisun- and shaded-lemon. Supplementary UV-B radiation (22 kJ m(-2) day(-1) UV-BBE) induced UV-B-absorbing compound synthesis in on-tree and postharvest lemons. Two minutes of supplemental UV-B irradiation in summer lemons produced a strong increment (300%) of UV-B-absorbing compound content, whereas in winter lemons a slight increase (30%) was observed only after 3 min of irradiation. By contrast, UV-B-absorbing compound accumulation was not observed in albedo. MDA accumulation showed approximately a similar trend of UV-B-absorbing compounds. According to our results, solar UV-B was not required for UV-B-absorbing compound accumulation in lemon peel. Relationships between UV-B-absorbing compounds, MDA, reactive oxygen species and pathogen protection are also discussed.

Influence of sample treatment on ESR signal of irradiated citrus.

ESR spectra of the hard seed cover and kernel coating of irradiated orange and tangerine fruits were obtained under different sample drying conditions to analyze the effect of treatment on ESR line at g = 2.0033 (line A). The spectra shows almost the same lines that appear in stalks, achenes, seeds and skins of fresh fruit. The peak-to-peak intensity of the line A of the spectra shows a linear variation with dose in the range studied (up to 5 kGy) under controlled sample preparation. Q-band ESR spectra shows that this line is composed for three different lines from different species. A1, A2 and A3. The A2 and A3 lines are associated with dose but grow also during drying of the sample and are probably due to 'cellulosic' components of the seed cover. The A1 line appears only when sample is dried and is probably associated with the quinones of the internal kernel coat.

Estabilidad del contenido de vitamina C y algunos indicadores químicos en mandarinas tratadas con radiaciones gamma / Stability of vitamin C contents and some chemical indicators in mandarin oranges treated with gamma radiations

Se investigaron los cambios del contenido de vitamina C, sólidos solubles, acidez y ph en mandarinas de la variedad "Dancy", irradiadas a 5 dosis diferentes de 0,25 a 1,5 kGy y almacenadas durante 21 días de 12 a 15 -C aproximadamente, con el objetivo de establecer el grado de afectación de esas variables. Se observó una tendencia a la disminución del contenido de vitamina C, sólidos solubles y el porcentaje de acidez con el incremento de la dosis recibida; el ph se mantuvo estable para todas las dosis. En todos los grupos estudiados se observaron diferencias significativas entre el contenido inicial de vitamina C y los contenidos a los 10 y 21 dias de almacenamiento

Estabilidad del contenido de vitamina C y algunos indicadores químicos en mandarinas tratadas con radiaciones gamma / Stability of vitamin C contents and some chemical indicators in mandarin oranges treated with gamma radiations

Se investigaron los cambios del contenido de vitamina C, sólidos solubles, acidez y ph en mandarinas de la variedad "Dancy", irradiadas a 5 dosis diferentes de 0,25 a 1,5 kGy y almacenadas durante 21 días de 12 a 15 -C aproximadamente, con el objetivo de establecer el grado de afectación de esas variables. Se observó una tendencia a la disminución del contenido de vitamina C, sólidos solubles y el porcentaje de acidez con el incremento de la dosis recibida; el ph se mantuvo estable para todas las dosis. En todos los grupos estudiados se observaron diferencias significativas entre el contenido inicial de vitamina C y los contenidos a los 10 y 21 dias de almacenamiento