Scielo RSS <![CDATA[Brazilian Journal of Plant Physiology]]> vol. 23 num. 3 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Establishment of sensitive and resistant variety of tomato on the basis of photosynthesis and antioxidative enzymes in the presence of cobalt applied as shotgun approach</b>]]> Cobalt (Co) affords both beneficial as well as toxic effects to plants. The present study was performed with an aim to find out the varietal differences among five tomato cultivars against the Co induced changes in growth, photosynthesis, nitrate reductase (E.C., carbonic anhydrase (E.C., antioxidative enzymes i.e. peroxidase (E.C., catalase (E.C., superoxide dismutase (E.C. and that of proline content. Seeds of tomato (varieties, K-25, NTS-9, NBR-Uday, Sarvodya, and Malti) were soaked in 0, 100, 200 or 300 µM CoCl2 for 0, 4, 8, 12 h (shotgun approach) and sampled at 30 days after sowing. All the varieties showed significantly different response to different treatment combinations. Despite substantial varietal difference, increased Co concentration caused concomitant decrease in growth, photosynthesis and the activity of nitrate reductase and carbonic anhydrase. However, the activity of antioxidant enzymes and that of proline content increased with the increased concentration of Co as well as duration of soaking in all the varieties. Out of the varieties, K-25 possessed maximum antioxidative enzyme and proline content that represent its most resistant nature against the toxic effect of Co. The order of susceptibility/sensitivity was K-25 > NTS-9 > NBR-Uday > Sarvodya > Malti. <![CDATA[<b>Antioxidant and other biochemical defense responses of <i>Macrotyloma uniflorum</i> (Lam.) Verdc. (Horse gram) induced by high temperature and salt stress</b>]]> High temperature and salinity are the major ecological factors challenging crop productivity in the arid and semiarid regions of the world. Effects of high temperature (43-45°C) and salt stress (0.6 M) on Macrotyloma uniflorum (Lam.) Verdc. (Horse gram), were evaluated in terms of antioxidants and antioxidant enzymes. Both treatments caused typical stress responses in this tropical leguminosae. Oxidative stress indicators such as H2O2, TBARS, and proline were significantly elevated. Similarly, the antioxidant enzymes superoxide dismutase (SOD; EC, guaiacol peroxidase (POX; EC and acid phosphates (AP; EC were significantly elevated while catalase (CAT; EC was reduced. These treatments had contrasting effects on glutathione reductase (GR; EC1.6.4.2) and β-amylase (EC While temperature stress caused increase in GR and decrease in β-amylase, salt stress caused a counter effect. Contrast was also observed in ascorbate and glutathione which increased in temperature stress and reduced in salt stress. SDS-PAGE analysis indicated entirely different protein profiles in temperature and salt stressed seedlings. Growth rate and fresh mass were affected to same extent, relative to their controls. Taken together these data describes the similarities and peculiarities of key biochemical responses of Horse gram to high temperatures and salinity. <![CDATA[<b>Intraspecific variation in sensitivity to ambient ultraviolet-B radiation in growth and yield characteristics of eight soybean cultivars grown under field conditions</b>]]> The present study was conducted with eight cultivars of soybean (Glycine max) to determine the effect of exclusion of solar UV-B on the vegetative growth (plant height, leaf area, no. of nodes), UV absorbing compounds (implicated in UV protection) and crop yield (No. of pods and seed weight) and to determine the cultivar difference in their sensitivity to ambient UV-B. Exclusion of solar UV-B enhanced the vegetative growth and yield of all the soybean cultivars. The results showed a significant inverse association between the enhancement in vegetative growth and number of pods among the cultivars tested, indicating differences in the carbon partitioning amongst the cultivars by the way of exclusion of solar UV-B. NRC-7, Pusa-24 and JS-335 showed maximum promotion in vegetative growth and less enhancement in crop yield after solar UV-B exclusion. Kalitur, JS71-05, Hardee, PK-472 and PK-1029 showed improved performance both in terms of number of pods/plant and seed weight after solar UV-B exclusion. An enhancement in the crop yield by exclusion of solar UV-B indicated poor response of the cultivar to the ambient solar UV-B; these cultivars would be more suitable at latitudes, which received less UV-B. According to UV-SI, sensitivity of eight Indian soybean cultivars to ambient level of UV-B (280-320 nm) radiation had the following descending order; PK-472 > JS-335 > Hardee > Kalitur > JS71-05 > Pusa-24 > NRC-7 > PK-1029. These findings suggest the way to select the best-suited cultivar for particular latitude. <![CDATA[<b>Bioactive compounds and antioxidant capacities in the flavedo tissue of two citrus cultivars under low temperature</b>]]> Antioxidants production is amongst the physiological responses of plants to protect their tissues from oxidative damages caused by chilling and freezing stresses. Indeed, cold tolerance of plants is related to production of reactive oxygen species (ROS) scavengers to combat oxidative stress. In this study, two citrus cultivars including Citrus sinensis 'Siavaraz' and Citrus limon 'Lisbon' grown at the north of Iran were examined to compare antioxidants changes including total flavonoid, total phenol and total antioxidant capacities (TAC) in the flavedo tissue of the fruits under various low temperature treatments of control (15 ºC), 3, 0, -3 and -6 ºC. The results indicated that total flavonoid content and TAC in Citrus limon 'Lisbon' was significantly higher than in Citrus sinensis 'Siavaraz'. During the treatments, both cultivars showed a significant increase in the flavonoid content. Meanwhile, total phenol content significantly increased from 15 to -6 ºC in Citrus limon 'Lisbon' and from 15 to 0 ºC in Citrus sinensis 'Siavaraz'. These results suggest that the biosynthesis of phenolics and flavonoids in flavedo of citrus fruit in response to low temperature might be correlated with environmental adaptation rather than antioxidant response. <![CDATA[<b>Changes in growth, pigment content and antioxidants in the root and leaf tissues of wheat plants under the influence of exogenous salicylic acid</b>]]> The effect of various concentrations of salicylic acid (SA) on the growth, pigment content and the activity of antioxidants was investigated in the laboratory grown wheat plants. The root and shoot growth was affected at higher concentration of SA in early days of growth. The activities of catalase (CAT), ascorbate peroxidase (APX) and guaicol-specific peroxidase (POX) declined with the application of SA (50, 500 and 1000 µM), the decrease being more pronounced with the increase in SA concentrations both in the root and leaf tissues. On the other hand superoxide dismutase (SOD) activity increased with the application of SA. At low concentrations, SA has no effect on the activities of these enzymes in vitro. Salicylic acid at higher concentrations (5- and 10 mM) though inhibited CAT activity, the activities of APX and POX remain unchanged. High concentration of SA increased the level of H2O2 and malondialdehyde both in root and leaf tissues. Thus, SA though has been reported to be a signal molecule for inducing various physiological and morphological attributes in plants, this study indicated the negative effect of the compound on growth and the activity of major enzymatic antioxidants. <![CDATA[<b>Phosphorus and nitrogen interaction</b>: <b>loss of QC identity in response to P or N limitation is antecipated in <i>pdr23</i> mutant</b>]]> Changes in root architecture are an important adaptive strategy used by plants in response to limited nutrient availability to increase the odds of acquiring them. The quiescent center (QC) plays an important role by altering the meristem activity causing differentiation and therefore, inducing a determinate growth program. The arabidopsis mutant pdr23 presents primary short root in the presence of nitrate and is inefficient in the use of nucleic acids as a source of phosphorus. In this study the effect of the pdr23 mutation on the QC maintenance under low phosphorus (P) and/or nitrogen is evaluated. QC identity is maintained in wild-type in the absence of nitrate and/or phosphate if nucleic acids can be used as an alternative source of these nutrients, but not in pdr23. The mutant is not able to use nucleic acids efficiently for substitute Pi, determinate growth is observed, similar to wild-type in the total absence of P. In the absence of N pdr23 loses the expression of QC identity marker earlier than wild-type, indicating that not only the response to P is altered, but also to N. The data suggest that the mutation affects a gene involved either in the crosstalk between these nutrients or in a pathway shared by both nutrients limitation response. Moreover loss of QC identity is also observed in wild-type in the absence of N at longer limitation. Less drastic symptoms are observed in lateral roots of both genotypes.<hr/>Alteração na arquitetura da raiz é uma estratégia adaptativa importante, usada pelas plantas, em resposta à disponibilidade limitada de nutrientes para aumentar as chances de adquirí-los. O centro quiescente (CQ) participa na mudança da atividade meristemática, causando diferenciação e induzindo um programa determinado de crescimento. O mutante de arabidopsis pdr23 apresenta raiz primária curta na presença de nitrato e é ineficiente no uso de ácidos nucléicos como fonte de fósforo. Neste estudo, o efeito da mutação de pdr23 sobre a manutenção do CQ sob baixo fósforo e/ou nitrogênio é avaliado. Na ausência de nitrato e/ou fósforo, se ácidos nucléicos são usados como fonte alternativa destes nutrientes, a identidade do CQ é mantida na planta silvestre, mas não em pdr23. O mutante não é capaz de usar eficientemente os ácidos nucléicos como substituto de fosfato, crescimento determinado é observado, similar à planta silvestre na ausência de P. Na ausência de N, pdr23 perde a expressão do marcador de identidade do CQ antes que a planta silvestre, indicando que as respostas a P e a N estão alteradas. Os dados sugerem que a mutação em pdr23 afete um gene envolvido na interação destes nutrientes ou em uma rota usada na resposta à limitação de ambos. Além disso, perda da identidade do CQ é também observada na planta silvestre na ausência de N em longos períodos. Sintomas menos dramáticos são observados nas raízes laterais de ambos os genótipos. <![CDATA[<b>Photosynthetic activity in the rootstock of hybrid peach trees submitted to water restriction and flooding</b>]]> This study aimed to evaluate the effect of flooding and water restriction (drought) on the photosynthetic activity in plants of the hybrid rootstock 'GxN-9' (Prunus dulcis Mill. × Prunus persica L. Bastsch), grown in a greenhouse. Chlorophyll fluorescence and gas exchange were analyzed in plants of approximately 12 months. The reduction of photosynthetic activity in both the stresses were associated with decreased carboxylation efficiency, but without affecting the internal concentration of carbon dioxide. The JIP-test parameters revealed changes in the energy flux processes demonstrating that in terms of flooding the rootstock GxN-9 the rate of photosynthetic performance significantly decreases, resulting in a considerable decrease in net assimilation rate. The JIP-test analysis was efficient in determining the thresholds mainly of the flood response, proving to be useful in exploration of the photosynthetic activity as a physiological marker of the stress tolerance. <![CDATA[<b>Seeds of Amazonian Fabaceae as a source of new lectins</b>]]> Seeds from fifty native Amazonian Fabaceae species (representing subfamilies Caesalpinioideae, Mimosoideae and Faboideae) were screened for the presence of new lectins. Their crude protein extracts were assayed for hemagglutinating activity (HA). The protein fractions of Anadenanthera peregrina, Dimorphandra caudata, Ormosia lignivalvis and Swartzia laevicarpa exhibited HA, and this activity was inhibited by galactose or lactose but not by glucose or mannose. The crude extract of S. laevicarpa exhibited HA activity only after ion exchange chromatography, and its lectin was further purified by affinity chromatography on immobilized lactose. Despite the large number of lectins that have been reported in leguminous plants, this is the first description of lectins in the genera Anadenanthera, Dimorphandra and Ormosia. The study of lectins from these genera and from Swartzia will contribute to the understanding of the evolutionary relationships of legume lectins in terms of their protein processing properties and structures.