Geraldo Luiz Gonçalves Soares

Species-specific changes in tissue morphogenesis induced by two arthropod leaf gallers in Lantana camara L. (Verbenaceae)

When different cecidogenous species attack the same plant species, each one causes distinct plant tissue reorganisation, and forms typical gall structures. Two Lantana camara L. leaf galls induced by Aceria lantanae (Cook) (Acarina: Eriophyidae) and Schismatodiplosis lantanae (Rubsaamen) (Diptera: Cecidomyiidae) were collected in a subspontaneous population at Rio Grande do Sul, Brazil. A. lantanae crinckle galls were uni- or multi-chambered and contained several mites, caused by several leaf foldings, and consisted of hyperplasic epidermis and parenchyma. S. lantanae induced uni-chambered pouch galls inhabited by one larvae or pupa. This gall consisted predominantly of hypertrophied spongy parenchyma. Our results documented how these herbivores acted in cells with the same initial morphogenetic competence, altering leaf pattern, and inducing their specific extended phenotype.

Reações de defesas químicas e estruturais de Lonchocarpus muehlbergianus Hassl. (Fabaceae) à ação do galhador Euphalerus ostreoides Crawf. (Hemiptera: Psyllidae)

Galhas sao estruturas vegetais induzidas em resposta ao ataque de organismos indutores. Euphalerus ostreoides (Psyllidae) induz galhas sobre a face adaxial de foliolos nas nervuras de segunda ordem de Lonchocarpus muehlbergianus (Fabaceae). Secoes anatomicas foram realizadas e comparados os tecidos de foliolos sadios com os de galhas imaturas e maduras. Testes histoquimicos para deteccao de derivados fenolicos, flavonoides, ligninas, lipidios e amido foram realizados para avaliar o impacto quimico causado pelo galhador. Em termos estruturais, a perda de sinuosidade das celulas epidermicas, a neoformacao de tricomas, de celulas condutoras e de fibras foram os caracteres mais conspicuos observados em decorrencia da inducao das galhas. Destaca-se a hiperplasia e hipetrofia do mesofilo com manutencao da estratificacao, a producao de goticulas lipidicas e amido, flavonas, flavonois e flavanonas nos tecidos das galhas. Contudo, a formacao de cristais de oxonio pela adicao de acido sulfurico somente nos tecidos das galhas foi uma caracteristica marcante. Os resultados sugerem que L. muehlbergianus esta submetida a alto estresse oxidativo induzido pela acao do E. ostreoides. Conclui-se que as alteracoes sao consideradas reacoes de defesa da planta contra herbivoria e mecanismos de adaptacao que em conjunto favorecem o estabelecimento do galhador nos tecidos vegetais.

Relações entre o teor de fenóis totais e o ciclo das galhas de Cecidomyiida e em Aspidosperm a spruceanum Müll. Arg. (Apocynaceae)

Morphological alterations detected in several plant species due to gall induction are commonly followed by chemical changes fundamental to the establishment and maintenance of the host plant-gall maker system. The study of phenolic contents variation and its relation to gall development in Aspidosperma spruceanum-Cecidomyiidae system through a year-time detected two insect life cycles. The level of infestation was high, getting up to 87%, and the Cecidomyiidae preferentially oviposited in internervural region. Seasonal variation in phenolic contents in healthy and galled leaves detected in A. spruceanum was primarily related to abiotic conditions. Even though the levels of phenolic contents might get a maximum of 10 mg EAT g-1, which indicated a non stimulating cell chemical environment to gall induction and herbivore survivorship, A. spruceanum gall maker surpassed this chemical barrier, and might also be favored by the chemical protection against its natural enemies, that phenolic contents might confer.

Potencial alelopático do capim-annoni-2 (Eragrostis plana Nees) na germinação de sementes de gramíneas perenes estivais

Among plant strategies to invade and dominate the plant community, the release of alelochemicals is prominent. These compounds are present in all plant parts, principally, in root exudates, leaves and their degraded parts. They are released in the environment through volatile or soluble emanations, translocated in water. Capim-annoni-2 is an invasive exotic Poaceae of rangeland vegetation with allelopatic potential. To test this effect, plant structures from the mid part of capim-annoni-2 were collected and cut in small pieces of 0.5cm and placed in three covering levels of 0, 50 and 100% in gerboxes covered with germitest blotters over the cut material. A hundred seeds of Paspalum notatum Flugge, P. regnellii Mez, Megathyrsus maximus B. K. Simon and S. W. L. Jacobs, Setaria sphacelata (Schumach) Staff and C. E. Hubb ex Chipp and Lactuca sativa L., were placed to germinate as controls. A randomized complete block design was used with four replications. The allelopatic effect was observed on the seed germination after the beginning of capim-annoni-2 plant tissue decomposition. Seeds with high speed germination, such as M. maximus and P. reginelli as well as L. sativa, escaped the allelopatic effect. The most damaged species in their germination course were P. notatum e S. sphacelata. The germination injury was proportional to the gradient increase of the capim-annoni-2 covering tissue with the exception of P. reginelli which showed, at 50% capim-annoni-2 covering level, an increase in germination, but at 100% level there was a significant germination reduction. The capim-annoni-2 allelopathic effects occur during plant tissue decomposition. Seeds with precocious germination escape these effects. The late germination of P. notatum and S. sphacelata exposed them to the capim-annoni-2 allelopathic effects. P. reginelli germination was stimulated at 50% covering level to capim-annoni-2, but at maximum level there was a significant germination decrease in its seeds.

The imbalance of redox homeostasis in arthropod-induced plant galls: Mechanisms of stress generation and dissipation☆

BACKGROUND Galls have specialized tissues for the protection and nutrition of the inducers, and these tissues have been studied from the developmental and histochemical perspectives. Recently, the role of oxidative stress in galls has been tested histochemically through detection of H2O2 in gall tissues. SCOPE OF REVIEW Developmental processes and cytological events are revisited from the perspective of the redox-potential balance in both the apoplast and symplast, especially concerning the accumulation of reactive oxygen species (ROS). MAJOR CONCLUSIONS The redox potential is imbalanced differently in the apoplast and symplast at gall sites, with the apoplast having lower antioxidant-buffering capacity than the symplast. The strategies to recover redox-potential homeostasis involve the dissipation of ROS by scavenging molecules, such as phenolics, flavonoid derivatives, tocopherol, and enzyme systems. GENERAL SIGNIFICANCE Insect galls are good models to test developmental hypotheses. Although the exact mechanisms of gall induction and development have not been elucidated at the biochemical and biophysical levels, modulation of the redox potential is involved in the crucial steps of gall initiation and establishment. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Volatile compounds of Baccharis punctulata, Baccharis dracunculifolia and Eupatorium laevigatum obtained using solid phase microextraction and hydrodistillation

In this work the qualitative chromatographic profiles of the volatile oil obtained with fresh chopped leaves of Baccharis punctulata, Baccharis dracunculifolia and Eupatorium laevigatum, using HS-SPME were compared with their hydrodistilled oils. Several Brazilian native plant species have not yet been studied regarding their volatile compounds composition. Conventional techniques employed for the investigation of volatile compounds, such as hydrodistillation, may impart chemical changes to the original oil composition. The use of HS-SPME provides alternative milder extraction conditions, preventing chemical transformations and supplying complementary information about volatiles composition. Coumarin and coumaran were detected by the first time among volatile components of E. laevigatum leaves after mechanical damage, only when using HS-SPME. Differences and similarities perceived between volatile compounds profiles using both extraction techniques are discussed, showing that they are complementary and may bring insight about fresh leaf volatiles playing infochemical roles and about chemical transformations caused by hydrodistillation.

Avaliação da atividade repelente do timol, mentol, salicilato de metila e ácido salicilico sobre larvas de Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae)

The repellent activity of thymol, menthol, salicylic acid and methyl salicylate on Boophilus microplus larvae was studied. These substances were tested according to their solubility: emulsions in 1% aqueous dimethylsulphoxide or in pure water. Three concentrations were tested for each substance, 1.0%, 0.5% and 0.25%, with five repetitions for each. Approximately 100 larvae at 21 days of age were placed on the base of wooden sticks and then observed for repellent action every two hours, during twelve hours. The results obtained from the higher concentrations showed that the four substances caused alterations on the larvae behavior. However, thymol (65% of mortality and 35% of repellency), menthol (80% of repellency) and methyl salicylate (80% of repellency) were the most efficient.

The influence of caffeine and thymol on the survival, growth and reproduction of Subulina octona (Brugüière, 1789) (Mollusca, Subulinidae)

Subulina octona is a terrestrial snail which serves as an intermediate host for the parasites. It is also an agricultural pest. The aim of this work was to assess, during 120 days, the effects of caffeine and thymol at 2.5 g/L and 5 g/L on the hatchability, survival after hatching, growth and reproduction of S. octona under the laboratory conditions. A total of 240 eggs, 240 juveniles aged 10-day-old, and 240 aged 30-day-old were tested. The results showed that thymol (at 2.5 g/L and 5 g/L) and caffeine (at 5 g/L) acted as ovicides. In the 10-day-old juveniles, caffeine at 5 g/L caused 25% mortality and at 2.5 g/L it caused 30% mortality. Thymol at 2.5 and 5 g/L caused 20 and 22.5% mortality, respectively. In the 30-day-old juveniles, caffeine at 5 g/L caused 47.5% mortality.

Cytotoxicity of essential oils from two species of Heterothalamus (Asteraceae)

Essential oils arewidely foundinplant species.Theycanbeinvolvedinavariety of ecologicalinteractions and may act as inhibitors of germination, suppressing root apical-meristem growth in some species. The present study aimed to determine the potential cytotoxicity of essential oils from leaves of Heterothalamus psiadioides Less. and H. alienus (Sprengel) O.Kuntze on root tips of lettuce (Lactuca sativa L.) and onion (Allium cepa L.). Lettuce seeds germinated with essentialoilsfromH.psiadioidesandH.alienushadareducedmitoticindex(MI)foralltreatments.Onionseedlingstreated withH.psiadioidesoilshowedadecreaseinMI,andseedlingstreatedwithH.alienusoilshowedadecreaseinMIof89%in themostconcentratedtreatment.Analysisoftheresultsshowedchromosomalabnormalities,includingstickiness,c-mitosis, micronuclei and anaphase bridges in lettuce and onion root tips exposed to essential oils of Heterothalamus.

Protein content and electrophoretic profile of insect galls on susceptible and resistant host plants of Bauhinia brevipes Vogel (Fabaceae)

Gall induction, mediated by insect-herbivore chemical stimuli, is the result from anatomical and biochemical alterations in the host-plant tissues that provides shelter, food and defence against natural enemies and the harsh environment to the gall inducer. Schizomya macrocapillata Maia (Diptera, Cecidomyiidae) induces galls on Bauhinia brevipes Vogel (Fabaceae); the galls are spherical, with long reddish hairs that cover the adaxial wall surface of the gall, and a protuberance is observed on the abaxial leaf surface. Some plants are resistant to gall formation and, in many cases, this formation is inhibited by hypersensitive reaction. In the present work, samples from different parts of the non-galled and galled tissues from resistant and susceptible plants were carefully dissected. Indicating elevated metabolic activity, the protein concentration was 1.5–4.5-fold higher in the abaxial portion of the galls than in any other tissues, regardless of whether the galls were from resistant or susceptible plants. Different tissues from susceptible and resistant plants had distinct protein concentrations, and the fractionation of the proteins by SDS–PAGE and silver-staining showed shared and/or specific polypeptides. We hypothesise that specific proteins, possibly from distinct metabolic pathways, are involved in the physiological processes that determine whether the plant shows total and/or partial host resistance to the galling-insect attack.