Role of sucrose for tobacco guard cell osmoregulation: osmolyte or substrate?

A characterization of transgenic tobacco plants overexpressing potato sucrose synthase 3 gene (NtSuSy3) under control of KST1 promoter was performed in order to analyze the role of sucrose metabolism on GC osmoregulation. Also, we performed a metabolic flux analysis in guard cell enriched epidermal fragment (EF) of Nicotiana tabacum in order to investigate changes in GC metabolism during stomatal aperture light-induced. NtSuSy3 plants showed higher stomatal conductance, transpiration rate, whole plant transpiration, and net photosynthetic rate than wild type (WT). Several changes in GC metabolism were observed in transgenic plants are discussed in the text. In different stomatal aperture light-induced experiments, it was observed a decrease in sucrose content, while no changes were detected in the sugar content in the medium; suggesting that the sugars decreased observed is due to breakdown and not efflux of GC. Using a feeding strategy in EF submitted to NaH13C03 followed by LC-qTOF-MS analysis, a 13 C-enrichment in sucrose, malate, fumarate and glutamine were observed. The possible function of these metabolites for GC osmoregulation are discussed in the text. Taken together, the data showed here provide evidence for another role of sucrose for GC osmoregulation. Our data suggest that sucrose breakdown, not just sucrose accumulation, can be performed to induce stomatal opening in tobacco.A papel da sacarose em CG foi investigado através da caracterização de plantas de Tabaco transgênicas superexpressando a isoforma 3 do gene sacarose sintase (NtSuSy3) sob controle do promotor KST1 bem como por experimentos de análise de fluxo metabólico utilizando fragmentos epidérmicos enriquecidos com CG (EF) durante abertura estomática induzida pela luz. As plantas NtSuSy3 mostraram aumentos na condutância estomática, fotossíntese e nas taxas de transpiração a nível foliar e de planta inteira. As alterações observadas no metabolismo de CG das plantas transgênicas são discutidas no texto. Observou-se uma redução nos níveis de sacarose em diferentes experimentos de abertura estomática induzida pela luz, enquanto que os níveis de sacarose no meio não foram alterados, sugerindo que a sacarose foi degradada no simplasto de CG. A análise via LC-qTOF-MS de experimentos com EF submetidos a NaH13C03 durante abertura estomática induzida pela luz mostraram um enriquecimento de 13 C em sacarose, malato, fumarate e glutamins. As possíveis funções exercidas por esses metabólitos são discutidas no texto. Em conjunto, os dados desse trabalho sugerem que a degradação da sacarose no simplasto de CG pode ser um mecanismo importante para a abertura estomática de Tabaco induzida pela luz.Fundação de Amparo à Pesquisa do Estado de Minas Gerai

Survival and initial growth of native tree species implanted in degraded pastures.

O presente trabalho teve por objetivo analisar e comparar o crescimento inicial de espécies nativas de diferentes grupos sucessionais implantadas em área de pastagem degradada e monitorar a evolução da biodiversidade local por meio da regeneração natural. O estudo foi desenvolvido no município de Jateí, estado de Mato Grosso do Sul, Brasil. Analisou-se, durante um ano, altura de plantas, diâmetro do colo, projeção da copa e taxa de sobrevivência, em três subáreas de 400 m2: (I) declividade de 10%, (II) declividade de 14% e (III) barranco erodido. Propôs-se um delineamento inteiramente casualizado com os representantes de cada espécie constituindo o número de repetições. As espécies pioneiras e secundárias iniciais apresentaram maior crescimento e adaptação ao ambiente, destacando-se Maclura tinctoria, Myracrodruon urundeuva, Cedrela odorata, Peltophorum dubium e Anadenanthera colubrina, as quais podem ser indicadas para restauração florestal de áreas degradadas.This study aimed to monitor the initial growth and survival of Brazilian native species from different successional groups grown in Permanent Preservation Areas degraded by pasture activity. The study was conducted in Jateí city, State of Mato Grosso do Sul, Brazil. Plants were analyzed for one year, the plant height, stem diameter, crown projection and survival in three sub-areas. It was proposed a completely randomized design with individuals of each species representing the number of repetitions. The pioneer species and early secondary showed higher growth and adaptation to the environment, especially Maclura tinctoria, Myracrodruon urundeuva, Cedrela odorata, Peltophorum dubium and Anadenanthera colubrina which may be indicated for recovery plant of degraded pasture

Physiological characterization of gun4 mutant of Arabidopsis thaliana under light stress

Mutações em genes denominados GUN (Genome UNcoupled) têm auxiliado na compreensão das rotas de transdução de sinais do cloroplasto que controlam a expressão de genes fotossintéticos nucleares. Nesse sentido, o genótipo gun4 tem sido caracterizado em aspectos bioquímicos e moleculares, no entanto pouco se sabe sobre aspectos fisiológicos desse mutante. Diante disso, de forma a complementar essa caracterização fenotípica, o objetivo desse trabalho foi avaliar as respostas fotossintéticas do mutante gun4 de Arabidopsis thaliana sob diferentes níveis de luz. Plantas gun4, na ausência de estresse luminoso, apresentaram níveis de clorofila a e b, fluorescências mínima (Fo) e máxima (Fm) de folhas adaptadas ao escuro e rendimento quântico de dissipação não regulada de energia do fotossistema II (ΦNO) reduzidos em 20%, 26%, 18% e 32%, respectivamente, enquanto que o rendimento quântico efetivo do FSII (ΦFSII) e o coeficiente de extinção fotoquímico (qL) foram 11% e 20% maiores, respectivamente. Valores maiores de ETR (taxa de transporte de elétrons), ΦFSII e qL também foram observados em gun4 sob diferentes intensidades luminosas, demonstrando que este fenótipo transfere de forma mais eficiente a energia luminosa absorvida no complexo coletor de luz do FSII para o processo fotossintético. A taxa de assimilação líquida de carbono (A) e a condutância estomática (gs) foram 43% e 61% menores em gun4, respectivamente. Porém, não houve diferença no fluxo de absorção de 14CO2, sugerindo que a menor magnitude de A seja devido a uma restrição difusional ao influxo de CO2. Após 14 h de estresse, não houve diferença em A e os valores da taxa de transporte de elétrons (ETR) e ΦFSII foram reduzidos em 35% e 50%, respectivamente, tanto nas plantas gun4 como no tipo selvagem (WT). Entretanto, o rendimento quântico potencial do FSII (Fv/Fm) decresceu significativamente apenas em WT, sugerindo que gun4 possa minimizar, mais eficientemente, efeitos fotoinibitórios. Isto se evidencia, adicionalmente, nos maiores valores de coeficiente de extinção não fotoquímico (qN) e rendimento quântico de dissipação regulada de energia do FSII (ΦNPQ). Em conjunto, esses fenótipos fotoquímicos de gun4 podem explicar o maior aumento (48%) na conectância global da rede fotoquímica após 28 h de estresse, demonstrando a maior capacidade deste genótipo em ajustar seu aparato fotossintético em resposta ao estresse luminoso. Por fim, os resultados encontrados neste trabalho demonstraram a alta capacidade do genótipo gun4 em dissipar o excesso de energia luminosa absorvida sob estresse e, apesar da forte redução no teor de clorofila, transferir esta mais eficientemente. Isso sugere a existência de um mecanismo de adaptação dos fotossistemas de forma a compensar a redução na absorção de luz, indicando um valor importante deste mutante para explorar os mecanismos que controlam a plasticidade dos complexos protéicos fotoquímicos.Mutations in GUN (Genome UNcoupled) genes have helped to understand the pathways of the chloroplast signal transduction that control the expression of nuclear photosynthetic genes. In this context, the gun4 genotype has been characterized in biochemical and molecular aspects. However, little is known whether this mutant produces a phenotype physiological aspects. In order to complement the phenotypic characterization of gun4 genotype, the aim of this study was evaluate the photosynthetic responses of gun4 plants of Arabidopsis thaliana under different levels of light and under light stress. The gun4 plants, in the absence of light stress showed reduced levels of chlorophyll a and b, minimal (Fo) and maximal (Fm) fluorescence in dark-adapted leaves, and quantum yield of unregulated energy dissipation of photosystem II (ΦNO) in 20%, 26%, 18% e 32%, respectively. Also, the effective quantum yield of the FSII (ΦFSII) and photochemical quenching (qL) were 11% and 20% higher, respectively. Higher values of ETR (electrons transport rate), ΦFSII and qL were also found in gun4 under different light intensities, showing that gun4 can maximize the transfer of light energy absorbed in the light harvest complex of FSII for the photosynthetic process. The rate of net carbon assimilation (A) and stomatal conductance (gs) were 43% and 61% lower in gun4 respectively, despite no difference in the flow of absorption of 14CO2 was observed, suggesting that the lower magnitude of photosynthesis is due to resistance to influx of CO2. After 14 hours of light stress, there was no difference in A, and the values of the electron transport rate (ETR) and ΦFSII were reduced by 35% and 50% respectively, both in gun4 and wild type (WT) plants. However, the quantum yield potential of FSII (Fv/Fm) decreased significantly only in WT, suggesting that gun4 may have a greater ability to minimize photoinhibitory effects. These results provide additional evidences for the higher non-photochemical quenching (qN) and quantum yield of regulated energy dissipation of the gun4 FSII (ΦNPQ). Together, the photochemical phenotypes of gun4 may explain the increase (48%) in the photochemical global network connectance after 28 hours of stress, demonstrating the greater ability of this genotype to adjust its photosynthetic apparatus in response to light stress. Finally, the results found in this study demonstrated that gun4 transfers and dissipates more efficiently the excess of light energy absorbed under light stress condition, despite a strong reduction in chlorophyll content. The results suggest the existence of a mechanism for the adjustment of the photosystem in order to offset the reduction of light absorption, indicating the importance of this mutant to explore the mechanisms that control the plasticity of the photochemical protein complex.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Efeitos da radiação ultravioleta-C sobre a simetria e morfoanatomia foliar de Rapanea ferruginea (Ruiz et. Pav) Mez. (Myrsinaceae) - DOI: 10.4025/actascibiolsci.v31i2.861

This study analyzed the effects of UV-C radiation on the development of Rapanea ferruginea leaves. Young plants were selected at six months of age, previously identifying the leaves that had already differentiated on the 3rd, 4th, 6th 8th and 9th nodes. After the selection, the plants were divided into three groups and subjected to UV-C radiation for 30, 60 or 120 minutes. The anatomic study was made by using usual techniques of cut and coloration. The morphometric analyses were made by determining three points on the midvein of the leaf, measuring from left (L) and right (R) borders to each of those points. The symmetry deviations, maximum length and width of the limb were measured and the values were submitted to Anova and the Tukey-test (p < 0.05). The responses of R. ferruginea to the UV-C were expressed by variations in the symmetry as well as morphoanatomic injuries, mainly in the palisade parenchyma and mesophyll. The differentiation of leaves did not follow a morphometric pattern, characterizing no directional asymmetry, i.e., fluctuating asymmetry. This study emphasizes the importance of multiscale observations for the determination of plant responses under stress, since several leaves showed anatomic injuries but no morphologic injuries.Neste estudo, analisaram-se os efeitos da radiação UV-C sobre o desenvolvimento de folhas de Rapanea ferruginea. Plantas jovens foram selecionadas com seis meses de idade identificando-se as folhas já diferenciadas do 3º, 4º, 6º, 8º e 9º nó. Posteriormente, as plantas foram divididas em três grupos e submetidas à radiação UV-C por 30, 60 ou 120 min. seguidos. Para o estudo anatômico, foram utilizadas técnicas usuais de corte e coloração. As análises morfométricas foram realizadas determinando-se três pontos ao longo da nervura central da folha, medindo-se das bordas esquerda (E) e direita (D) até cada um desses pontos. Determinaram-se também os desvios de simetria, o comprimento e a largura máxima do limbo, submetendo os valores à Anova e ao teste de Tukey (p < 0,05). As respostas de R. ferruginea à UV-C foram expressas por variações na simetria, bem como por injúrias morfoanatômicas, sobretudo ao parênquima paliçádico e mesofilo. A diferenciação das folhas não seguiu um padrão morfométrico, caracterizando, assim, uma assimetria não-direcional, ou seja, flutuante. Este estudo ressalta a importância de observações multiescalares para a determinação de respostas de plantas ao estresse, já que algumas folhas apresentaram danos anatômicos, porém não morfológicos

Efeitos da radiação ultravioleta-C sobre a simetria e morfoanatomia foliar de Rapanea ferruginea (Ruiz et. Pav) Mez. (Myrsinaceae) = Effects of ultraviolet-C radiation on symmetry and morphoanatomy of Rapanea ferruginea (Ruiz et. Pav) Mez. (Myrsinaceae) leaves

Neste estudo, analisaram-se os efeitos da radiação UV-C sobre odesenvolvimento de folhas de Rapanea ferruginea. Plantas jovens foram selecionadas com seis meses de idade identificando-se as folhas já diferenciadas do 3º, 4º, 6º, 8º e 9º nó. Posteriormente, as plantas foram divididas em três grupos e submetidas à radiação UV-Cpor 30, 60 ou 120 min. seguidos. Para o estudo anatômico, foram utilizadas técnicas usuais de corte e coloração. As análises morfométricas foram realizadas determinando-se três pontos ao longo da nervura central da folha, medindo-se das bordas esquerda (E) e direita (D) até cada um desses pontos. Determinaram-se também os desvios de simetria, o comprimento e a largura máxima do limbo, submetendo os valores à Anova e ao teste de Tukey (p This study analyzed the effects of UV-C radiation on the development of Rapanea ferruginea leaves. Young plants were selected at six months of age, previously identifying the leaves that had already differentiated on the 3rd, 4th, 6th 8th and 9th nodes. After the selection, the plants were divided into three groups and subjected to UV-C radiation for 30, 60 or 120 minutes. The anatomic study wasmade by using usual techniques of cut and coloration. The morphometric analyses were made by determining three points on the midvein of the leaf, measuring from left (L) and right (R)borders to each of those points. The symmetry deviations, maximum length and width of the limb were measured and the values were submitted to Anova and the Tukey-test (p < 0.05). The responses of R. ferruginea to the UV-C were expressed by variations in the symmetry aswell as morphoanatomic injuries, mainly in the palisade parenchyma and mesophyll. The differentiation of leaves did not follow a morphometric pattern, characterizing no directional asymmetry, i.e., fluctuating asymmetry. This study emphasizes the importance of multiscale observations for the determination of plant responses under stress, since several leaves showed anatomic injuries but no morphologic injuries

Quebra de dormência em sementes de Sesbania virgata (Cav.) Pers

Forest species with hard seeds often pose considerable problems to nursery managers because their hard and impermeable seed coats hinder and delay germination. Therefore, this work aimed to determine the most efficient, practical and low cost methodology to overcome dormancy in Sesbania virgata (Cav.) Pers. Seed, a specie with potential for recovery of degraded areas. The seeds were submitted to chemical scarification by immersion in sulfuric acid during a period of 5, 10, 20 and 30 minutes, mechanical scarification and heat treatment. After the scarification the seeds were submitted to germ test in germination chambers at 25oC and photoperiod of 14 h. Treatment with mechanical scarification showed the highest germination percentage (98%), followed by chemical scarification for 30 minutes (57%). The heat treatment in spite of obtaining a higher germination percentage than the controls had abnormal development of seedlings and is not therefore recommended for seeds of S. virgata. From the parameters utilized in this study, we recommend the use of the mechanical scarification to overcome dormancy of S. virgata seeds

Guard cell-specific down-regulation of the sucrose transporter SUT1 leads to improved water use efficiency and reveals the interplay between carbohydrate metabolism and K+ accumulation in the regulation of stomatal opening

Sucrose is a key metabolite in guard cell (GC) regulation and has been proposed to form a key metabolic connection between mesophyll cells and GCs. However, the importance of sucrose transport across the GC plasma membrane in stomatal movements remains to be determined. Here, we characterized transgenic tobacco plants expressing an antisense gene construct for the SUCROSE TRANSPORTER 1 (SUT1) driven by the GC specific promoter KST1. GCs of transgenic plants contained less sucrose, more starch and had increases in K+ content. Lower GC sucrose content was associated with lower stomatal conductance that, in turn, led to a lower transpiration rate and higher carbon isotope composition ratio compared to wild type plants. Although the transgenic plants showed reduced growth under optimal water supply condition, they showed improved growth compared to wild type plants under osmotic stress and demonstrated lower water consumption that was correlated with higher relative water content under water-deficit conditions. This demonstrates the desiccation postponement phenotype of these plants together with an improved tolerance to water deficit. Taken together, our results indicate that SUT1 has an important role in stomatal movements and suggest that genetic manipulation of GC sucrose transport could be used to obtain plants with greater water use efficiency