Sidnei Deuner

Tolerance of Sesbania virgata plants to flooding

Sesbania virgata (Cav.) Pers. is a bush, pioneer and occurs naturally in Brazil. It belongs to the Fabaceae family and it is indicated for recovery of degraded areas because of its rusticity and capacity to tolerate flooding. The present research was carried out to investigate the ability of S. virgata plants to adapt to flooding conditions. Plants containing six expanded leaves were placed in masonry tanks and were subjected to the following conditions: control (well watered), soil-waterlogging (water to the setup level of 1 cm above the soil surface – roots and parts of the stems flooded) and complete submergence (whole plant flooded). The evaluations were conducted on the day of the stress induction and after 7, 14, 21, 28, 35, 42, 49 and 56 days of the treatment. After 15 days of return to normoxic environment, plant survival was assessed. Growth (height, dry mass of shoots and roots), vigour, carbohydrate content and the activity of enzymes involved in anaerobic metabolism (lactate dehydrogenase, pyruvate decarboxylase and alcohol dehydrogenase) were also evaluated. Our results suggested that sesbania plants are tolerant to flooding, because they can survive being submerged for 56 days. The reasons for this tolerance include the accumulation and use of carbohydrates in the leaves and roots, maintenance of growth and the activation of anaerobic metabolism, particularly in steps catalysed by the enzymes pyruvate decarboxylase and alcohol dehydrogenase.

Stomatal behavior and components of the antioxidative system in coffee plants under water stress

Coffee (Coffea arabica) plants show a positive relationship between stomatal closure and formation and accumulation of H2O2. However, for coffee plants under water restriction such relationship has never been studied. The objective of the present study was evaluate the stomatal movement and the antioxidant capacity of coffee seedlings under different water regimes. Eight months old coffee seedlings of cv. Catuai IAC 99 were submitted to field capacity, gradual and total suspension of irrigation during a period of 21 days. Evaluations of leaf water potential (Ψw) were performed in the beginning of the morning, and stomatal resistance, transpiration rate and vapor pressure deficit were determined at 10 am and 5 pm. All biochemical and enzymatic determinations were performed in leaves collected at 5 pm. Evaluations and samplings were performed at three days intervals. There was no variation in Ψw during the evaluated period for plants in field capacity. However, an expressive decrease of Ψw following day 12, reaching values near -2.5 MPa at the end of the experiment was observed for plants submitted to gradual suspension of irrigation. For plants submitted to total suspension of irrigation, Ψw decreases after the sixth day, reaching -2.5 MPa at day 15. The decay of Ψw in plants submitted to gradual and total suspension of irrigation reflected in increased stomatal resistance and in a decreased transpiration rate leading to an increase in hydrogen peroxide formation and, on final stages, increase in lipid peroxidation. As a conclusion, an increase in the activity of antioxidant enzymes as well as in the levels of ascorbate and dehydroascorbate was observed, which act in the detoxification of free radicals formed as result of the water stress.

Características fisiológicas e anatômicas de plantas de sibipiruna submetidas à hipoxia

Plants in their natural environment are subject to adverse conditions, and the stress periods can be short or long. Some species develop mechanisms that make them bear the adverse conditions, allowing their survival. The aim of this study was to evaluate the anatomic and physiological responses in the initial development of Sibipiruna plants submitted to hypoxia. Plants with three to four leaves fully expanded were subjected to three treatments: plants without flooding, flooded on roots and totally flooded. Evaluations were carried out in the starch, total soluble sugars and reducing sugars levels in the leaves and roots collected every five days, for 30 days. Anatomical characteristics were evaluated 15 days after the beginning of each treatment. The largest reduction in starch level in leaves and in roots was observed in plants completely flooded. For total soluble sugars and reducing sugars were observed behavior similar to that achieved in starch However, the plants which had flooded roots, in some periods of assessment, had levels, mainly in the roots, higher than the plants without flooding. These plants also showed higher stomatal density than the other treatments. For the thickness of the cortex and the cylinder vascular roots, a reduction was observed for the flooded treatment, which completely flooded plants had a higher apoplastic barrier imposed by thickening in phi, which is characterized by the formation of septa in cells near the endodermis.

Development of rice seedlings grown from pre-hydrated seeds and irradiated with gamma rays

Tecnicas como radiacoes ionizantes, utilizadas para induzir mutacoes constituem ferramenta eficaz no aumento de variabilidade genetica em programas de melhoramento de especies de interesse economico. Neste trabalho, objetivou-se verificar o efeito de diferentes doses de radiacao gama Co60 em sementes previamente embebidas sobre a emergencia e o crescimento inicial de plântulas de duas cultivares de arroz. Lotes de sementes com 25% de umidade das cultivares BRS Querencia e BRS Fronteira foram irradiados com doses de zero (controle), 50, 100, 150 e 200 Gy, sendo, em seguida, semeadas em bandejas contendo solo e mantidas em casa de vegetacao. Os resultados mostraram que a radiacao gama afetou o desenvolvimento das plântulas, sendo que a maior dose testada (200 Gy) reduziu, significativamente, a emergencia e o indice de velocidade de emergencia. Os parâmetros de crescimento apresentaram maior reducao na cv. BRS Querencia. Na atividade das enzimas antioxidantes, a superoxido dismutase expressou pouca variacao para os periodos avaliados. Ja, a ascorbato peroxidase e catalase mostraram expressivo aumento na cv. BRS Fronteira aos 14 DAS, seguidas de incremento para as duas cultivares na atividade da ascorbato peroxidase aos 28 DAS. A maior capacidade antioxidante observada na cv. BRS Fronteira conferiu uma maior tolerância ao estresse causado pela radiacao gama.

Respostas fisiológicas em cultivares de soja submetidas ao alagamento em diferentes estádios

A soja e um dos produtos agricolas de maior importância no Brasil, e segundo maior produtor mundial. A tolerância ao excesso de umidade do solo e da rapida recuperacao com o termino do alagamento sao caracteristicas desta cultura, porem, a deficiencia de oxigenio, causada pelo excesso de agua, e um dos fatores determinantes que pode reduzir sua produtividade. O objetivo deste trabalho foi verificar o comportamento de tres cultivares de soja ao alagamento em diferentes estadios de desenvolvimento, por meio de analise da producao de massa seca, metabolismo de carboidratos e atividade das enzimas do metabolismo anaerobio. O experimento foi desenvolvido na Universidade Federal de Lavras (MG), em 2007. As cultivares BRS 267, BRS 257 e BRS 213 foram submetidas a 15 dias de alagamento, nos estadios V6 e V8 e 11 dias no estadio R4. Os resultados revelaram reducao na producao de massa seca nos tratamentos alagados no estadio V8 para a cultivar BRS 267 e no estadio V6 para BRS 257 e BRS 213; esta ultima foi a mais tolerante ao alagamento, pois obteve o menor decrescimo de massa seca em relacao ao controle. O alagamento tambem induziu aumento nos teores de amido e acucares soluveis totais nas folhas, assim como maior atividade das enzimas alcool desidrogenase e piruvato descarboxilase para as tres cultivares, quando comparadas a seus respectivos controles. Ja para a enzima lactato desidrogenase, essa diferenca foi menos expressiva. Esses resultados revelam comportamentos distintos comparando as tres cultivares.

Carboidratos não estruturais em tubérculos de batata recondicionados após o armazenamento sob diferentes temperaturas

The levels of total soluble carbohydrates and reducing sugars were quantified in tubers of potato genotypes (Atlantic, Perola, Asterix and C-1786-6-94) stored under different temperatures (4, 12 and 20oC) for 30 and 60 days and after a reconditioning period of 30 days of storage. Before each harvest, the tubers were processed and divided in sub samples and then liofilizated. The liofilizated material was analyzed for total soluble carbohydrates and reducing sugars content. Higher amounts of total soluble carbohydrates were found in the Clone C-1786-6-94 before harvest. When stored during 30 days at 4oC all the genotypes presented an increase of the levels of total soluble carbohydrates and reducing sugars, with difference in the rates. The storage for more than 30 days at 4oC resulted in different response among genotypes. The storage at 12oC during 30 days increased the levels of sugars, and the storage during 60 days presented a tendency to decrease reducing sugars. In the reconditioning process under temperatures from 4 to 20oC occurred accentuated reduction in the level of reducing sugars and total soluble carbohydrates. The transfer from 12 to 20oC resulted in a strong lowering of the reducing sugar levels and total soluble carbohydrates. The storage at 20oC presented a small occasional flotation in the sugar levels, with tendency to decrease during the storage period.

Chlorophyll a fluorescence as indicative of the salt stress on Brassica napus L.

The effects of salinity stress on chlorophyll fluorescence and the growth of Brassica napus L were investigated. The chlorophyll a fluorescence transient were recorded and analyzed according to the JIP-test which can quantify PSII performance. Salt stress resulted in decreased leaf area and dry matter compared with the control treatment (0 mM NaCl). The most pronounced effects of salt stress were observed with 200 mM NaCl, and the hybrids displayed different levels of sensitivity to stress. The Performance Index (PIABS) was the most sensitive parameter to salt stress, which suggests that this parameter can be used to screen genotypes for salt tolerance.

Adubação foliar e via solo de nitrogênio em plantas de milho em fase inicial de desenvolvimento

Considerado o nutriente mais importante, tanto no incremento da producao de graos como no teor proteico destes, o nitrogenio (N) e tambem o elemento que mais onera a cultura do milho. Neste trabalho, objetivou-se verificar se a aplicacao foliar de nitrogenio influencia o acumulo de proteinas e parâmetros de crescimento de plantas jovens de milho em comparacao com a aplicacao de ureia via solo. Para tanto, plantas jovens do hibrido de milho BR 206 receberam aplicacoes de ureia como fonte de N via foliar e via solo nas concentracoes de zero; 0,5% e 1,0%. As plantas foram cultivadas em casa-de-vegetacao sendo realizadas tres aplicacoes de N, a primeira aos seis dias apos a emergencia (DAE) num volume de 10 mL por planta e as duas seguintes aos 10 e 14 DAE com 20 mL cada. Aos 18 DAE as plantas foram coletadas e as analises procedidas. Para altura de plantas, volume radicular, area foliar, materia seca da parte aerea e raizes, observou-se maior eficiencia da adubacao foliar, principalmente ao nivel de 0,5% de ureia. O fornecimento de ureia a 1,0% via solo proporcionou aumento significativo no teor de proteinas nas folhas. Tais resultados sugerem que a adubacao foliar pode ser uma maneira eficiente para complementar o que e absorvido pelas raizes, no entanto nao deve ser utilizada como fonte unica de N inorgânico as plantas.

Above-Optimum Temperature-Induced Differential Photosynthetic and Roots Morphometric Responses in Two Contrasting Rice Genotypes.

Temperature thresholds during the rice (Oryza sativa L.) cycle development have been reported to affect plant metabolism. Therefore, this study aimed to evaluate the effects of the above-optimal temperature on photosynthetic and morphometric parameters in two contrasting irrigated rice genotypes (BRS Querência—sensitive and Nagina 22 (N22)—tolerant). Plants of both genotypes were grown in rhizotrons and always maintained under two temperature conditions: Out—under environmental temperature conditions, and In—rhizotrons inside a plastic structure, which increased the temperature about 3 °C to 5 °C above the external one. In the genotype N22, there was an increase (twofold higher) in CO2 assimilation in plants cultivated under elevated temperature (In). In BRS Querência, the stomatal conductance (gs) and transpiration rate (E) decreased upon high temperature. The rise in the temperature also negatively impacted in the modulated fluorescence parameters in both genotypes. Increases in root dry weight (RDW) and shoot dry weight (SDW) were also observed in the genotype N22 when compared to BRS Querência upon temperature rise. In general, the N22 genotype showed greater response to the above-optimal temperature due to its intrinsic thermotolerance traits over BRS Querência. Thus, N22 appeared as a potential donor of heat tolerance genes aiming to obtain new cultivar to face current global warming.

Morphophysiological and biochemical alterations in Ricinus communis L. seeds submitted to cobalt60 gamma radiation

This study aimed to evaluate the radiosensitivity of castor bean seeds after applications of different doses of Cobalt60 gamma radiation. Seeds were pre-soaked for 24 hours in distilled water and then irradiated with 50, 100, 150, and 200 Gy, except the control. Sowing was performed in trays, which contained soil as substrate and were maintained in a greenhouse. The electrical conductivity, emergence, emergence speed index, growth parameters and activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, and catalase) were evaluated in the leaves and roots of castor bean seedlings. Gamma radiation did not affect the electrical conductivity of the seeds; however, at a dose of 200 Gy, the emergence and emergence speed index of the seedlings was negatively affected. An analysis of the morphophysiological parameters revealed a reduction in seedling size as the radiation dose increased. There was a significant increase in superoxide dismutase and ascorbate peroxidase activities at higher radiation doses in the leaves, but not in roots. Thus, the analysis of all the variables suggests a response pattern as to the morphophysiological and biochemical changes of castor bean seedlings due to the increase of gamma radiation, which may serve as a tool for generating greater genetic variability.