Scielo RSS <![CDATA[Brazilian Journal of Plant Physiology]]> http://www.scielo.br/rss.php?pid=1677-042020090003&lang=en vol. 21 num. 3 lang. en <![CDATA[SciELO Logo]]> http://www.scielo.br/img/en/fbpelogp.gif http://www.scielo.br <![CDATA[<b>Photosynthetic capacity of three phytoplanktonic species measured by a pulse amplitude fluorometric method</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300001&lng=en&nrm=iso&tlng=en During photosynthesis, absorbed energy that is not used in photochemical reactions dissipates as fluorescence. Fluorescence provides important information on the physiological conditions of the studied organisms and its measurement is widely used by plant physiologists and can be valuable in phytoplankton studies. We describe a method adapting a plant fluorometric equipment to measure the photosynthetic capacity of microalgae. Unialgal cultures of three planktonic chlorophytes were exposed to 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of photosystem II, at concentrations of 0.1, 1.0 and 10.0 µmol.L-1. Estimates were made of photosynthetic parameters, including operational and potential photosystem II quantum yield and electron transport rate between photosystems, using algal cells concentrated on glass-fiber filters. The technique allowed reliable measurements of fluorescence, and detection of distinct levels of inhibition. Physiological or morphological characteristics of the selected species might provide an explanation for the observed results: differences on the surface/volume ratio of the cells and colony morphology, for example, were associated with contrasting resistance to the toxicant. To characterize inhibition on phytoplanktonic photosynthesis, we suggest operational quantum yield and electron transport rate as best parameters, once they were more sensitive to the DCMU toxicity.<hr/>Durante os eventos fotossintéticos, a energia absorvida que não é usada em reações fotoquímicas pode ser dissipada como fluorescência. Sua medida fornece importantes informações acerca das condições fisiológicas dos organismos, sendo amplamente utilizada na fisiologia vegetal e podendo ser valiosa nos estudos do fitoplâncton. Este estudo descreve um método no qual um equipamento elaborado para a realização de medidas de fluorescência em plantas é utilizado para medir a capacidade fotossintética de microalgas. Culturas unialgais de três clorófitas planctônicas foram expostas a três concentrações de 3(3,4-diclorofenil)-1,1-dimetiluréia (DCMU), um inibidor do fotossistema II. Foram quantificados alguns parâmetros fotossintéticos, como os rendimentos quânticos efetivo e potencial do fotossistema II e a taxa de transporte de elétrons entre os fotossistemas. Para tal, as células algais foram concentradas em filtros de fibra de vidro. Esta técnica permitiu a quantificação da fluorescência proveniente do aparato fotossintético destas microalgas, possibilitando a detecção de diferentes níveis de inibição, segundo a espécie. Características fisiológicas ou morfológicas das espécies poderiam justificar os resultados observados: diferenças na razão superfície/volume das células e na forma das colônias, por exemplo, foram associadas aos níveis distintos de resistência ao DCMU. Para a avaliação da inibição da fotossíntese fitoplanctônica, nós sugerimos o rendimento quântico efetivo e a taxa de transporte de elétrons como os parâmetros mais adequados, uma vez que foram os mais sensíveis à toxicidade do DCMU. <![CDATA[<b>Response of <i>Cucumis sativus</i> L. seedlings to Pb exposure</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300002&lng=en&nrm=iso&tlng=en In this study, the effects of lead (Pb) on growth, photosynthetic pigments concentration, lipid peroxidation, electrolyte leakage percentage (ELP), protein oxidation, aminolevulinate dehydratase (ALA-D; E.C. 4.2.1.24), ascorbate peroxidase (APX; E.C. 1.11.1.11), catalase (CAT; E.C. 1.11.1.6) and superoxide dismutase (SOD; E.C. 1.15.1.1) activities, and ascorbic acid (AsA), non-protein thiol groups (NPSH) and total soluble protein concentrations in cucumber seedlings (Cucumis sativus L.) were investigated. Seedlings were grown in vitro in an agar-solidified substrate containing three Pb levels as (C2H3O2)Pb.3H2O (0, 100, 400, and 1000 µmol L-1) for 10 d. Increasing Pb concentrations in substrate enhanced Pb concentration in both roots and shoot. Pb accumulated at a higher amount in roots. Root length and total fresh weight were decreased at the two highest Pb concentrations. Cucumber showed no reduction in shoot length and total dry weight at any Pb level. The highest Pb concentration decreased water content and ALA-D activity as well as increased malondialdehyde, carbonyls and total soluble protein concentrations. Carotenoids concentration enhanced at 100 and 400 µmol Pb L-1, while chlorophyll concentration and ELP were not affected by Pb stress. Activity of APX was inhibited while the activities of CAT and SOD were increased at all Pb concentrations. AsA was enhanced at 400 and 1000 µmol Pb L-1 whereas NPSH were increased only at the highest Pb concentration. Therefore, high Pb-exposure caused oxidative stress, and the antioxidant system of the cucumber seedlings was not sufficient to revert it, contributing for growth reduction.<hr/>No presente estudo, os efeitos do chumbo (Pb) sobre o crescimento, a concentração de pigmentos fotossintéticos, a peroxidação lipídica, a percentagem de extravazamento de eletrólitos (ELP), a oxidação protéica, a atividade das enzimas aminolevulinato desidratase (ALA-D; E.C. 4.2.1.24), peroxidase do ascorbato (APX; E.C. 1.11.1.11), catalase (CAT; E.C. 1.11.1.6) e dismutase do superóxido (SOD; E.C. 1.15.1.1) e as concentrações de ácido ascórbico (AsA), de grupos tióis não-protéicos (NPSH) e de proteínas solúveis totais foram investigados em plântulas de pepino (Cucumis sativus L.). As plântulas foram cultivadas in vitro em um substrato solidificado com ágar contendo três concentrações de Pb na forma de (C2H3O2)Pb.3H2O (0, 100, 400 e 1000 µmol L-1), durante 10 dias. O aumento da concentração de Pb no substrato ocasionou um aumento da concentração de Pb tanto nas raízes quanto na parte aérea. O Pb foi acumulado em maior quantidade nas raízes. O comprimento radicular e a matéria fresca total foram diminuídos nas duas maiores concentrações de Pb. O pepino não apresentou redução no comprimento da parte aérea e na matéria seca total nos tratamento de Pb. A maior concentração de Pb diminuiu o conteúdo de água e a atividade da ALA-D bem como aumentou as concentrações de aldeído malônico, de grupos carbonil e de proteínas solúveis totais. A concentração de carotenóides aumentou em 100 e 400 µmol Pb L-1, enquanto a concentração de clorofila e a ELP não foram afetadas pelo estresse com Pb. A atividade da APX foi inibida, enquanto as atividades da CAT e SOD foram aumentadas em todas as concentrações de Pb. A concentração de AsA aumentou sob 400 e 1000 µmol Pb L-1, enquanto a de NPSH aumentou somente na maior concentração de Pb. Portanto, a exposição a altas concentrações de Pb causou estresse oxidativo e o sistema antioxidante das plântulas de pepino não foi capaz de reverter esta situação, contribuindo para a redução no crescimento. <![CDATA[<b>Growth of Indian mustard (<i>Brassica juncea</i> L.) in response to salicylic acid under high-temperature stress</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300003&lng=en&nrm=iso&tlng=en Pots holding 7 day-old seedlings of Indian mustard (Brassica juncea L.) were subjected to differential temperature stress by exposing plants to 30 or 40ºC for 24 h. Seedlings were sprayed with double distilled water (DDW) or 10-5M salicylic acid (SA) at the 8-day stage and were sampled at 30 DAS. The plants exposed to temperature stress exhibited a significant (p < 0.05) decline in growth, and in levels of chlorophyll, nitrate reductase and carbonic anhydrase activities and photosynthetic parameters. A follow-up treatment with SA protected against the stress generated by temperature and significantly improved the above parameters. Antioxidative enzymes and levels of proline significantly increased in response to SA as well as to temperature stress. <![CDATA[<b>Growth, photosynthesis and leaf water potential in young plants of <i>Copaifera langsdorffii </i>Desf. (Caesalpiniaceae) under contrasting irradiances</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300004&lng=en&nrm=iso&tlng=en Growth and leaf nutrient content were compared in young potted plants of Copaifera langsdorffii in sunny and shaded areas without water stress. Besides, carbon assimilation and leaf water relations were evaluated by net photosynthesis, potential photochemical efficiency and leaf water potential during daily courses in dry and rainy periods under natural conditions in both contrasting irradiances. Higher values of total biomass, height and leaf area occurred in sunny than in shaded area. On the other hand, all young plants survived in shade under natural water stress probably by reason of fast and intense biomass accumulation in favor of roots in early development. There was no significant difference about nutrient concentration in leaves between plants growing in sunny and shaded areas. Net photosynthesis in shade increased occasionally when bunches of direct light reached the leaves. Theses sunflecks took place more frequently and at high intensity in dry period but they were more effective for net photosynthesis in rainy period. The ability of young plants to persist under natural conditions in contrasting irradiance up to 1,230 days after sowing could explain the wide distribution of C. langsdorffii in Cerrado physiognomies and in different types of forest.<hr/>O crescimento e o conteúdo de nutrientes nas folhas foram comparados em plantas jovens envasadas de Copaifera langsdorffii crescendo em área sob irradiância total e em área sombreada sem estresse hídrico. A assimilação de carbono e as relações hídricas foram avaliadas por meio da fotossíntese líquida, da eficiência fotoquímica potencial e do potencial hídrico foliar durante cursos diários no período seco e chuvoso nas duas áreas com irradiâncias contrastantes. Maiores valores de biomassa total, altura e área foliar ocorreram na área sob irradiância plena. As plantas jovens sobreviveram sob estresse hídrico em condições naturais na área sombreada provavelmente em função do rápido e intenso acúmulo de biomassa nas raízes logo no início do desenvolvimento. Não houve diferença significativa em relação à concentração de nutrientes entre as plantas crescendo sob diferentes regimes de iluminação. A fotossíntese líquida sob sombreamento aumentou ocasionalmente quando feixes de luz que atravessaram as copas atingiram diretamente as folhas de C. langsdorffii. Esses feixes de luz ocorreram com maior intensidade e mais freqüentemente no período seco, mas foram mais efetivos para a assimilação líquida no período chuvoso. A habilidade das plantas jovens persistirem em condições naturais sob os dois regimes contrastantes de irradiância até 1.230 dias após a semeadura pode explicar a vasta distribuição de C. langsdorffii nas diferentes fisionomias do Cerrado e em outras formações florestais. <![CDATA[<b>Morphological analysis and photosynthetic performance of improved papaya genotypes</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300005&lng=en&nrm=iso&tlng=en Brazil is the largest world producer of papaya and the third largest exporter despite of only 1.5 to 2.0% of its production is exported. Such an underexplored exportation potential highlight the necessity for physiological studies on new cultivars and hybrids to verify their agronomic and commercial viability. Two Brazilian states, Bahia and Espirito Santo, are responsible for 80% of national production. Papaya can also be an agricultural alternative to north / northeast of Rio de Janeiro, because the region is close to consumer centers and have similar environmental conditions of the most productive regions. Nevertheless, it is worth to develop cultivars that can express the highest yield potential in this region. The aim of this work was to characterize physiologically two hybrids developed for the north/northeast of Rio de Janeiro (UENF/Caliman 01 and JS12) in comparison with three top commercial genotypes (Golden, Sunrise Solo 7212 and Tainung) of Caricapapaya L. The cv. Golden presented the lowest shoot and root growth, the lowest height, shrunk diameter, specific leaf weight, less efficiency in electrons transport per sample area and show the lowest ability to synthesized total chlorophylls in comparison with the others genotypes. At noon, this genotype showed higher stomatal conductance, related to the leaf-air vapor pressure deficit, which lead to higher transpiration rate and intrinsic water use efficiency. No differences were detected in the photosynthetic rates among the five genotypes suggesting that the UENF`s hybrids are endowed with similar photosynthetic capacity and morphological characteristics to the top commercial genotypes. The relevance of this characterization to drive future successful genetic improvement programs will be discussed. <![CDATA[<b>Photo-oxidative stress in coconut seedlings</b>: <b>early events to leaf scorching and seedling death</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300006&lng=en&nrm=iso&tlng=en Experiments were conducted on coconut seedlings to delineate events of photo-oxidative stress damage. Studies on chlorophyll fluorescence indicated a clear case of excess light energy under high light conditions causing stress to coconut seedlings raised under coconut palms. Quantum yield of photo-chemistry of leaflets exposed to high light was significantly less than those under shade. Seedlings exposed to high light and then shifted to shade have shown significant improvement in quantum yield. Excess light energy harvested by chlorophyll antenna caused high non-photochemical quenching resulting in production of biologically toxic super oxide, hydrogen peroxide and hydroxyl radicals. It is apparent that photoinhibition of photosynthesis takes place due to i) PSII down regulation and ii) damage to PS II system in initial stages of exposure to excess light and under prolonged exposures inhibition is caused due to iii) chlorophyll bleaching and iv) damage to chloroplast and cell membrane integrity, followed by reduction in photosynthetically active leaf area because of scorching thus reducing canopy photosynthesis. Protein concentration in leaf tissue was higher in seedlings in high light conditions. Three distinct low molecular weight proteins with pI of 4.9, 8.4 and 10.15 having Mr less than 20,000 were found in seedlings exposed to high light intensities. Results clearly demonstrate the events that take place at early stage to subsequent cascading effects leading to the scorching and death of leaf and even seedling death under severe conditions. <![CDATA[<b>Glycinebetaine improves salt tolerance in vinal (<i>Prosopis ruscifolia</i> Griesbach) seedlings</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300007&lng=en&nrm=iso&tlng=en Glycinebetaine (GB) is a very important organic osmolyte that accumulates in a number of diverse groups of plants in response to environmental stress. In some plants, increased resistance to drought, salinity and low temperature has been achieved through exogenous application of GB. In this study, the effect of exogenously applied GB (8 mM) on the ability of vinal (Prosopis ruscifolia G.) plants to withstand NaCl stress was investigated. The dry biomass of vinal showed a decrease under salt stress, but in GB-treated plants exposed to the same stress, this reduction was mitigated. Sodium accumulated in the leaves of plants grown under saline conditions, but the addition of GB to salt-grown plants reduced Na+ content by 40%. Salinity significantly reduced the K+ concentration in leaves to 65% that of non-salinized controls. In the presence of GB, leaf K+ was comparatively higher, reaching as much as 90% of the control concentration. The sodium: potassium ratio in leaves was significantly higher in salt-stressed plants, but this ratio was lowered significantly by the addition of GB. When compared to control plants, NaCl stress increased malondialdehyde (MDA) concentrations by 95%, but GB application reduced the MDA concentration in these same NaCl-treated plants. In comparison to control plants, the activity of superoxide dismutase (SOD) increased by 52% in salt-stressed plants. The addition of GB to salt-treated plants stimulated SOD activity twice that of the non-salizined control. These results suggest that, in addition to protecting membranes, GB-enhanced salinity tolerance in vinal may involve an antioxidant mechanism involving enhanced SOD activity and improving the ion homeostasis under conditions of high salinity.<hr/>Glycinabetaína (GB) é um dos osmólitos orgânicos mais importantes que se acumulam em diversas plantas em resposta a estresses ambientais. Em algumas espécies, o aumento a resistência à seca, salinidade ou baixa temperatura foram conseguidos pela aplicação exógena da GB. Neste estudo foi investigado o efeito de GB aplicado exogenamente (8 mM) na habilidade do vinal (Prosopis ruscifolia Griesbach) para suportar o estresse salino induzido por NaCl. A biomassa seca das plantas diminuiu por efeito do tratamento salino, mas aumentou em plantas tratadas com GB. O Sódio (Na+) acumulou-se nas folhas das plantas crescidas sob estresse salino, mas a adição do GB às plantas tratadas com NaCl provocou uma diminuição de 40% no conteúdo de Na+. Em comparação às plantas controle, nas plantas tratadas com NaCl observou-se uma redução de 65% no conteúdo de potássio (K+). Na presença do GB, a concentração de K+ nas plantas sob estresse salino foi maior que nas plantas não tratadas com GB. A relação sódio: potássio aumentou significativamente nas plantas sob estresse salino, mas esta relação foi reduzida significativamente pela adição de GB. Quando comparado às plantas controle, o estresse induzido pelo NaCl aumentou a concentração do malondialdehyde (MDA) em 95%, mas a aplicação do GB reduziu a concentração de MDA em plantas tratadas com NaCl, indicando menor dano nas membranas. Em comparação às plantas controle, a atividade da superóxido dismutase aumentou em 52% nas plantas tratadas com NaCl. Em comparação ao controle, a adição do GB provocou um aumento de 100% na atividade da SOD nas plantas sob estresse salino. Estes resultados sugerem que, além do aumento na proteção de membranas, o incremento da tolerância à salinidade em plantas de vinal por efeito do tratamento com GB pode estar relacionado com o aumento na proteção enzimática do estresse oxidativo gerado pelo estresse salino por meio da estimulação da atividade da SOD e potencialização da homeostase iônica sob estresse salino. <![CDATA[<b>L-<i>myo</i>-InositoL-1- phosphate synthase from bryophytes</b>: <b>purification and characterization of the enzyme from <i>Lunularia cruciata </i>(L.) Dum</b>]]> http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1677-04202009000300008&lng=en&nrm=iso&tlng=en L-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4) catalyzes the conversion of D-glucose-6-phosphate to 1L-myo-inositol-1-phosphate, the rate limiting step in the biosynthesis of all inositol containing compounds. Myo-inositol and its derivatives are implicated in membrane biogenesis, cell signaling, salinity stress tolerance and a number of other metabolic reactions in different organisms. This enzyme has been reported from a number of bacteria, fungi, plants and animals. In the present study some bryophytes available in the Eastern Himalaya have been screened for free myo-inositol content. It is seen that Bryum corinatum, a bryopsid shows the highest content of free myo-inositol among the species screened. Subsequently , the enzyme MIPS has been partially purified to the tune of about 70 fold with approximately 18% recovery form the reproductive part bearing gametophytes of Lunularia cruciata. The L. cruciata synthase specifically utilized D-glucose-6-phosphate and NAD+ as its substrate and co-factor respectively. The optimum pH shown was 7.0 while the temperature maximum was at 30ºC. The enzyme activity was slightly stimulated by Mg2+ and Ca2+; remarkably stimulated by NH4+; slightly inhibited by Mn2+; highly inhibited by Cu2+, Zn2+ and Hg2+. The Km values for D-glucose-6-phosphate and NAD+ was found to be 0.80 and 0. 034 mM respectively while the Vmax values were 2.8 and 1.21 mM for D-glucose-6-phosphate and NAD+ respectively.