Physiological and biochemical responses of Eucalyptus seedlings to hypoxia

International audienceAbstractKey messageHypoxia promoted distinct changes in the levels of hormones, amino acids and organic acids in the roots and shoots of a seedling from 2Eucalyptusclones. These results indicate that modulation of hormone production, as well as specific chemical constituents associated with primary metabolism, contributes to the regulation of growth ofEucalyptusseedlings under hypoxic conditions.ContextAlthough floods in areas under Eucalyptus cultivation in Brazil negatively affect plant growth, chemical markers and/or indicators of hypoxia contributes to the regulation.sAimsThis study aimed to evaluate the hormonal and metabolic alterations induced by hypoxia on seedling growth.MethodsSeedlings of Eucalyptus urograndis clones VCC 975 and 1004 were grown in liquid solution and submitted to bubbling with air or with nitrogen. Levels of indol-3-acetic acid (IAA), abscisic acid (ABA), ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), primary metabolite profile and photosynthetic parameters were evaluated after fourteen days.ResultsHypoxia did not affect shoot dry mass of the seedlings. However, it decreased stomatal conductance and photosynthetic CO2 assimilation rate, and increased levels of ABA in the shoot. Hypoxia greatly reduced the dry mass and volume of roots, concomitantly with higher ACC and ethylene production. Moreover, hypoxia promoted distinct changes in IAA levels, and in amino acid and organic acid metabolism in roots and shoots.ConclusionThe biosynthesis of ABA, ethylene and IAA and its quantity in root tissues indicates the regulation of metabolism in response to hypoxia in Eucalyptus clones

A Herbivorous Mite Down-Regulates Plant Defence and Produces Web to Exclude Competitors

Herbivores may interact with each other through resource competition, but also through their impact on plant defence. We recently found that the spider mite Tetranychus evansi down-regulates plant defences in tomato plants, resulting in higher rates of oviposition and population growth on previously attacked than on unattacked leaves. The danger of such down-regulation is that attacked plants could become a more profitable resource for heterospecific competitors, such as the two-spotted spider mite Tetranychus urticae. Indeed, T. urticae had an almost 2-fold higher rate of oviposition on leaf discs on which T. evansi had fed previously. In contrast, induction of direct plant defences by T. urticae resulted in decreased oviposition by T. evansi. Hence, both herbivores affect each other through induced plant responses. However, when populations of T. evansi and T. urticae competed on the same plants, populations of the latter invariably went extinct, whereas T. evansi was not significantly affected by the presence of its competitor. This suggests that T. evansi can somehow prevent its competitor from benefiting from the down-regulated plant defence, perhaps by covering it with a profuse web. Indeed, we found that T. urticae had difficulties reaching the leaf surface to feed when the leaf was covered with web produced by T. evansi. Furthermore, T. evansi produced more web when exposed to damage or other cues associated with T. urticae. We suggest that the silken web produced by T. evansi serves to prevent competitors from profiting from down-regulated plant defences

Spider mite web mediates anti-predator behaviour

Herbivores suffer significant mortality from predation and are therefore subject to natural selection on traits promoting predator avoidance and resistance. They can employ an array of strategies to reduce predation, for example through changes in behaviour, morphology and life history. So far, the anti-predator response studied most intensively in spider mites has been the avoidance of patches with high predation risk. Less attention has been given to the dense web produced by spider mites, which is a complex structure of silken threads that is thought to hinder predators. Here, we investigate the effects of the web produced by the red spider mite, Tetranychus evansi Baker & Pritchard, on its interactions with the predatory mite, Phytoseiulus longipes Evans. We tested whether female spider mites recognize predator cues and whether these can induce the spider mites to produce denser web. We found that the prey did not produce denser web in response to such cues, but laid more eggs suspended in the web, away from the leaf surface. These suspended eggs suffered less from predation by P. longipes than eggs that were laid on the leaf surface under the web. Thus, by altering their oviposition behaviour in response to predator cues, females of T. evansi protect their offspring

Antipredator behaviours of a spider mite in response to cues of dangerous and harmless predators

Prey are known to invest in costly antipredator behaviour when perceiving cues of dangerous, but not of relatively harmless predators. Whereas most studies investigate one type of antipredator behaviour, we studied several types (changes in oviposition, in escape and avoidance behaviour) in the spider mite Tetranychus evansi in response to cues from two predatory mites. The predator Phytoseiulus longipes is considered a dangerous predator for T. evansi, whereas Phytoseiulus macropilis has a low predation rate on this prey, thus is a much less dangerous predator. Spider mite females oviposited less on leaf disc halves with predator cues than on clean disc halves, independent of the predator species. On entire leaf discs, they laid fewer eggs in the presence of cues of the dangerous predator than on clean discs, but not in the presence of cues of the harmless predator. Furthermore, the spider mites escaped more often from discs with cues of the dangerous predator than from discs without predator cues, but they did not escape more from discs with cues of the harmless predator. The spider mites did not avoid plants with conspecifics and predators. We conclude that the spider mites displayed several different antipredator responses to the same predator species, and that some of these antipredator responses were stronger with cues of dangerous predators than with cues of harmless predators

Programa de Controle da Doença de Chagas no Estado de São Paulo: sorologia de moradores como parte de investigação de unidades domiciliares com presença de triatomíneos vetores na década de 1990 The Chagas Disease Control Program of the São Paulo State: the contribution of serology to the epidemiological investigation of triatomine-infested domiciliary units during the 1990s

O Programa de Controle da Doença de Chagas (PCDCh) no Estado de São Paulo encontra-se na fase de vigilância entomológica, submetendo a exames sorológicos os moradores de unidades domiciliares (UDs), em que triatomíneos vetores tenham sido encontrados infectados por Trypanosoma cruzi. No decênio 1990-1999 foram trabalhadas localidades que, segundo graus de infestações no intra ou no peridomicílio, desencadearam trabalhos de rotina de busca desses vetores e de atendimento a notificações por parte de moradores. Em 1.415 UDs examinadas, 5.587 amostras de sangue foram obtidas, 87 (1,56%) das quais reagentes. Dessas, sete correspondiam a pessoas com menos de 29 anos de idade. As espécies mais freqüentemente associadas, em suas formas adultas, às UDs foram: Panstrongylus megistus, Triatoma sordida e T. tibiamaculata. Não foi observada associação entre UDs com sororreagentes e presença de triatomíneos infectados por Tr. cruzi (odds ratio = 1,498; 0,875 < OR < 2,564, 95% de confiança). Propõe-se utilizar inquéritos sorológicos amostrais no PCDCh, para investigar a situação prevalente em áreas identificáveis como de risco de transmissão, complementando-os com estudos isolados de Tr. cruzi aí obtidos.<br>The Chagas Disease Control Program in São Paulo State, Brazil, now in the entomological surveillance phase, includes a serological examination of individuals residing in domiciliary units infested with vector triatomines infected with Trypanosoma cruzi. From 1990 to 1999, this action included area in which triatomine searches were conducted either as a routine procedure, according to their levels of intra- or peridomiciliary infestation, or at the request of local residents. Among residents of the 1,415 UDs inspected, we collected 5,587 blood samples for serological examination, 87 of which (1.56%) tested positive, seven of which from individuals under 29 years of age. The species most frequently captured were Panstrongylus megistus, Triatoma sordida, and Triatoma tibiamaculata in the adult stage. No association was found between presence of seropositive residents and triatomines infected with Tr. cruzi (OR = 1.498; 0.875 < OR < 2.564, 95% C.I.). Our purpose was to use serological testing to investigate the situation of areas identifiable as being at risk of Chagas disease transmission and to compare the results with extant data about Tr. cruzi infection both in humans and vector triatomines