-The objective of this work was to characterize the morphoanatomy of roots and the yield traits of two corn hybrids contrasting for drought tolerance (DKB 390, tolerant; and BRS 1030, sensitive), at different stages of development. Water deficit was imposed for ten days, in a greenhouse, at three growth stages: V5, VT, and R3. These treatments were combined to generate cumulative stress during the plant cycle, as: V5VT, V5R3, VTR3, and V5VTR3. The following were analyzed: root anatomy; proportion of aerenchyma in the cortex; metaxylem number and diameter; phloem thickness; as well as morphological characteristics, such as root length, volume, and surface area, specific root length, length of fine roots, grain yield, and ear length and diameter. Development stage affected the responses to stress: DKB 390 showed the best performance for root morphoanatomy and yield traits, under drought stress, at the reproductive stages, mainly R3, and in the treatments with cumulative stress, especially V5VTR3; whereas BRS 1030 presented higher means for the studied parameters, mainly at the V5 and VT stages, but did not show a higher grain yield under water stress. The greater tolerance of the DKB 390 hybrid to water deficit is probably linked with a memory of pre-exposure to water stress at different growth stages.Index terms: Zea mays, aerenchyma, drought, endoderm, specific root length, WinRhizo. Morfoanatomia radicular em diferentes estádios de desenvolvimento e produtividade do milho sob estresse hídricoResumo -O objetivo deste trabalho foi caracterizar a morfoanatomia radicular e os atributos de rendimento de dois híbridos de milho contrastantes quanto à seca (DKB 390, tolerante; e BRS 1030, sensível), em diferentes estádios de desenvolvimento. A deficiência hídrica foi imposta por dez dias, em casa de vegetação, em três estádios de desenvolvimento: V5, VT e R3. Esses tratamentos foram combinados para gerar estresses acumulativos durante o ciclo da planta, como: V5VT, V5R3, VTR3 e V5VTR3. Foram analisados: anatomia radicular; proporção de aerênquima no cortex; número e diâmetro de metaxilema; espessura do floema; bem como características morfológicas, como comprimento, volume e área de superfície radicular, comprimento específico das raízes, comprimento de raízes finas, rendimento de grãos, e comprimento e diâmetro da espiga. O estádio de desenvolvimento influenciou as respostas ao estresse: DKB 390 apresentou o melhor desempenho quanto à morfoanatomia radicular e aos atributos de rendimento, quando submetido a estresse hídrico, nos estádios reprodutivos, sobretudo em R3, e nos tratamentos acumulativos de estresse, principalmente no V5VTR3; enquanto BRS 1030 apresentou as maiores médias para os parâmetros estudados, principalmente nos estádios V5 e VT, mas não apresentou maior rendimento de grãos sob estresse hídrico. A maior tolerância do híbrido DKB 390 ao estresse hídrico provavelmente relaciona-se à memória de exposição prévia ao estresse hídrico em diferentes estádios de desenvolvimento.Termos para indexação...

Typha domingensis (cattail) is a native macrophyte known by its capacity to tolerate several heavy metals effects and the potential use for phytoremediation. However, in despite that cadmium (Cd) is one of the most toxic pollutants; its effects in T. domingensis biology remain uninvestigated. Thus, the objective of this study was to study the tolerance of T. domingensis to cadmium contamination by evaluating its growth, Cd uptake, leaf anatomy and gas exchange. The experiment was designed using three cadmium concentrations (0, 10 and 50 µM) and ten replicates for 90 days. The cadmium uptake, growth, gas exchange, chlorophyll content and leaf anatomy were evaluated. Data was submitted to ANOVA and Scott-Knott test for P<0.05. Typha domingensis accumulates Cd proportionally to its concentration on the solution and the content of this metal was higher in roots as compared to shoots. Plants showed no significant modifications on growth parameters such as the biomass production, number of leaves, number of clones and the biomass allocation to organs. The photosynthesis, transpiration and chlorophyll content were not modified by Cd. Most anatomical traits evaluated were not modified by the metal but the stomatal density and the proportion of vascular tissues were reduced under 50 µM of Cd. In despite, the leaf anatomy showed no toxicity evidences for any Cd level. The absence of growth reduction and the stability of anatomical and physiological traits give insight about the Cd tolerance of this species. Therefore, T. domingensis is able to overcome Cd toxicity and shows potential for phytoremediation. Keywords

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Spectral quality is an important factor for in vitro development of explants in a bioreactor system. Based on the need to optimize micropropagation for E. grandis × E. urophylla clones, the aim of the study was to assess the spectral quality of in vitro multiplication in temporary immersion bioreactor (TIB). The tissue used to generate the explants (i.e., the nodal segment with 1 cm of length and two axillary bud without leaves) was previously in vitro established and multiplied, it derived from ministumps of E. grandis × E. urophylla clone grown in a semi-hydroponic system. The spectral quality of in vitro multiplication was assessed through five light sources (i.e., fluorescent lamp, red, green, blue, and yellow cellophane). Morphological and anatomical features of tissues grown in TIB were evaluated at 90 days. Based on the results, yellow and blue spectral qualities were the most suitable to be adopted for in vitro multiplication of E. grandis × E. urophylla, since they enabled lesser hyperhydricity, favors high number of shoots per explant and shoot length, as well as thicker mesophyll and spongy parenchyma; arise as an alternative for large-scale production of eucalypts clonal plants.

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