Selenium is an important element associated with enhancement of antioxidant activity in plants, microorganisms, animals, and humans. In Brazil, the information on Se in agricultural crops is lacking, though there are indications that low levels of Se are consumed by the population. The experiment was conducted under greenhouse conditions with pots containing 3 l of nutritive solution in a completely randomized factorial design, with seven Se concentrations (0, 2, 4, 8, 16, 32, and 64 µmol/l) and two forms of Se (sodium selenate -Na 2 SeO 4 and sodium selenite -Na 2 SeO 3 ), with six replicates. The application of Se as selenate at low concentrations is more appropriate for lettuce biofortification because it favors shoot biomass growth and Se levels in the shoot biomass. Selenium in both forms had two effects on lettuce plant metabolism: at low doses it acted as an antioxidant and enhanced plant growth, whereas at higher levels it reduced yield.

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RESUMOObjetivou-se verificar a existência de características de resistência à seca em mudas da cultivar Siriema em relação à cv. Catuaí. O experimento foi conduzido em viveiro com sombrite e plástico na área experimental do DBI/UFLA, MG. Foram utilizadas mudas de cafeeiros com seis meses de idade, seis a oito pares de folhas, provenientes do viveiro da Fundação Procafé, em Varginha, MG. Antes da indução dos tratamentos, as mudas foram irrigadas diariamente; depois, os tratamentos foram estabelecidos: um grupo continuava irrigado e outro grupo submetido à suspensão de rega. O período experimental foi de 10 dias e a unidade experimental foi composta por uma planta, sendo cinco repetições, dispostas em Delineamento Inteiramente Casualizado (DIC). Para a epiderme adaxial e abaxial, índice estomático e razão PP/LF não houve diferenças significativas em nenhuma situação estudada. Para o parênquima esponjoso no tratamento irrigado, o 'Siriema' apresentou maior espessura em relação à cv. Catuaí, enquanto que o parênquima paliçádico não apresentou diferenças. O limbo foliar do 'Siriema' foi mais espesso que o da cv. Catuaí, independentemente do tratamento. Os diâmetros polar e equatorial dos estômatos foram maiores no tratamento não irrigado para o 'Siriema'. Para a relação DP/DE e densidade estomática, o 'Siriema' não irrigado apresentou-se maior em relação à cv. Catuaí não irrigada. Nas condições deste experimento, os diâmetros polar e equatorial dos estômatos, relação DP/DE e densidade estomática permitiram discriminar satisfatoriamente os dois cafés estudados em termos de tolerância diferencial à seca, a favor do material 'Siriema'. Termos para indexação:Coffea arabica L., seca, anatomia foliar. ABSTRACTThis paper aimed to verify the existence of the drought characteristics of resistance in seedlings during coffee development. The material Siriema was compared to Catuaí cultivar. The experiment was conducted in greenhouse, with mesh screen and plastic in experimental area of DBI/UFLA/MG. One used coffee seedlings of 'Siriema' and 'Catuaí' of six months age, containing six to eight pairs of leaves, from the nursery house of Fundação Procafé in Varginha, MG. Before the treatment induction, the seedlings were daily irrigated, then the treatments were estabilished: one group continued to be irrigated and another one was submitted to irrigation suspension. The experimental period lasted 10 days. The experimental unit was composed by one plant with 5 replicates, disposed in freely randomized design. For the adaxial and abaxial epidermis, stomatic index and PP/LF ratio, and no significative differences were found. Considering the spongy perenchym in irrigated treatment, the 'Siriema' showed higher thickness than Catuaí cv., while for the palisada parenchyma there was no difference. The 'Siriema' leaf blade was thicker than 'Catuaí' independent of the treatment. The polar and equatorial diameters of the stomata were higher in non-irrigated treatment for 'Siriema'. For the DP/DE ratio for stomatic density the non-irrigated 'S...

RESUMO -Este trabalho teve como objetivo a avaliação das características anatômicas e fisiológicas de aguapé (Eichhornia crassipes) em resposta ao estresse por arsênio. As plantas de aguapé foram cultivadas em solução nutritiva hidropônica de Hoagland em casa de vegetação sob cinco concentrações de arsênio: 0,0; 0,25; 0,5; 1,0; e 2,0 mg L -1 por período de 20 dias. As plantas demonstraram aumento na taxa fotossintética, na condutância estomática, na transpiração e na relação Ci/Ca, bem como na atividade de todas as enzimas do sistema antioxidante, com maior atividade nas folhas em relação às raízes nos tratamentos contendo arsênio. As características anatômicas das folhas das plantas sob as maiores concentrações de arsênio mostraram aumento na densidade estomática, no índice estomático e na espessura do parênquima esponjoso. A anatomia radicular não evidenciou alterações decorrentes da intoxicação por arsênio e modificações nas características do xilema e floema, porém não houve prejuízos à sua estrutura e função. Dessa forma, o estresse por intoxicação pelo arsênio, nas concentrações testadas, não é evidente nas plantas de E. crassipes, e os mecanismos de tolerância são relacionados com modificações na anatomia e fisiologia das plantas.Palavras-chave: Eichhornia crassipes, anatomia ecológica, sistema antioxidante, fotossíntese.ABSTRACT -This work aimed to evaluate the anatomical and physiological characteristics of Eichhornia crassipes in response to arsenic stress. Plants of E. crassipes were grown in Hoagland hydroponic nutritive solution under greenhouse conditions at five arsenic levels: 0.0, 0.25, 0.50, 1.0 and 2.0 mg L -1 during 20 days. The plants showed an increase in photosynthetic rate, stomatal conductance, transpiration and Ci/Ca rate, as well as in the activity of all the enzymes in the antioxidant system, with higher activity in the leaves than in the roots, in all the treatments with arsenic. The anatomical characteristics observed on the leaves of the plants under higher arsenic levels showed an increase in stomatal density, stomatal index and spongy parenchyma thickness. Root anatomy showed no toxic evidences at any arsenic level; changes in the xylem and phloem characteristics were exhibited by the roots in the arsenic treatments, but no damage was caused to its structure and function. Thus, stress caused by arsenic intoxication at the levels tested, is not evident on E. crassipes plants, and the mechanisms of tolerance of E. crassipes are associated to anatomical and physiological changes.

This study aimed at verifying the lead tolerance of water hyacinth and at looking at consequent anatomical and physiological modifications. Water hyacinth plants were grown on nutrient solutions with five different lead concentrations: 0.00, 0.50, 1.00, 2.00 and 4.00 mg L -1 by 20 days. Photosynthesis, transpiration, stomatal conductance and the Ci/Ca rate were measured at the end of 15 days of experiment. At the end of the experiment, the anatomical modifications in the roots and leaves, and the activity of antioxidant system enzymes, were evaluated. Photosynthetic and Ci/Ca rates were both increased under all lead treatments. Leaf anatomy did not exhibit any evidence of toxicity effects, but showed modifications of the stomata and in the thickness of the palisade and spongy parenchyma in the presence of lead. Likewise, root anatomy did not exhibit any toxicity effects, but the xylem and phloem exhibited favorable modifications as well as increased apoplastic barriers. All antioxidant system enzymes exhibited increased activity in the leaves, and some modifications in roots, in the presence of lead. It is likely, therefore, that water hyacinth tolerance to lead is related to anatomical and physiological modifications such as increased photosynthesis and enhanced anatomical capacity for CO 2 assimilation and water conductance.