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Em 22 de fevereiro de 2022, a aluna Vict\u00f3ria de Carvalho do programa de P\u00f3s-Gradua\u00e7\u00e3o em Biodiversidade Vegetal e Meio Ambiente do Instituto de Pesquisas Ambientais (IPA), bolsista FAPESP (18\/13529-3), defendeu a tese de doutorado intitulada: \u201cToler\u00e2ncia e mem\u00f3ria \u00e0 seca na brom\u00e9lia ep\u00edfita Acanthostachys strobilacea <\/em>(Schult. & Schult.f.) Klotzsch\u201d.<\/p>\n A banca examinadora foi presidida pela orientadora, Dra. Catarina Carvalho Nievola (IPA), e contou com a participa\u00e7\u00e3o da Dra. Marisa Domingos (IPA), Dra. Helenice Mercier (Universidade de S\u00e3o Paulo), Dr. Gustavo Maia Souza (Universidade Federal de Pelotas), e Dr. Halley Caixeta de Oliveira (Universidade Estadual de Londrina).<\/p>\n ABSTRACT<\/strong><\/p>\n Epiphytic bromeliads depend on the atmosphere as a water source because they sustain themselves on trees, without direct contact between their roots and soil; therefore, they are naturally exposed to intermittent drought. Young plants of epiphytic bromeliads might be vulnerable to drought because they have a high predisposition to water loss and because several morphological adaptations to drought are not fully developed. Research on responses to drought and rewatering of juvenile epiphytic bromeliads can promote greater understanding of their tolerance to drought periods, which might be intensified due to climate change. Important components of plant drought defence include the antioxidant system, osmotic adjustment, and membrane permeability regulation through aquaporins. Many of these responses are regulated by signalling pathways composed of reactive oxygen and nitrogen species (RNS, ROS) and abscisic acid (ABA), activated during early drought. The epiphytic bromeliad Acanthostachys strobilacea<\/em> (Schult. & Schult.f.) Klotzsch, native to the Atlantic Forest and Cerrado, presents several drought adaptations (e.g.<\/em>, crassulacean acid metabolism, CAM), being an appropriate model for the evaluation of drought defence mechanisms in juvenile epiphytic bromeliads. The objective of this work was to evaluate three hypotheses regarding the response to drought and subsequent recovery in juvenile plants of A. <\/em>\u00a0strobilacea<\/em>, which are: (i) the first hours of drought exposure lead to an increase in the content of RNS, ROS and ABA and, subsequently, to the activation of defense mechanisms; (ii) plants show more intense biochemical defense responses after exposure to a second drought-rewatering cycle, indicating memory formation; (iii) short-term drought and rewatering result in modulation of the daily rhythm of CAM photosynthesis, associated with changes in aquaporin genes expression, anatomical pattern and water status.\u00a0 For the evaluation of the first two hypotheses, signalling molecules (e.g.,<\/em> RNS and ABA) and biochemical defence mechanisms (e.g.,<\/em> antioxidant activity and osmolyte content) were quantified.\u00a0 Gas exchange, water status parameters, and gene expression of aquaporins were evaluated for the validation of the third hypothesis. The first line of study showed that the increase in antioxidant enzymes activities, proline and osmotic adjustment occurred during 24 hours of drought concomitantly with peaks in the RNS content, suggesting the involvement of these molecules in drought signalling pathways.\u00a0 Contrary to expectations, ABA accumulation occurred later at 72 hours of exposure, being potentially related to the regulation of late responses to drought. The second study showed that the content of pigments, total amino acids and S-nitrosoglutathione reductase activity were intensified after a second exposure to a 14-day drought, performed after a cycle of 14 days of drought and 5 days of rewatering, confirming the second hypothesis. Finally, the third hypothesis was confirmed because a 14-day drought followed by one day of rewatering reversibly induced water remobilization in the hydrenchyma (water storage tissue), adjustments in aquaporins gene expression and in CAM photosynthesis.\u00a0 The present study provides evidence of physiological, biochemical, molecular, and morphological mechanisms of drought resistance in young A. strobilacea<\/em> plants, demonstrating that a pronounced defence capacity is present from early ontogenetic stages in this species. This work provides information for future studies on the drought response of epiphytes aiming to better understand the roles of RNS and ABA in signalling pathways, memory formation and aquaporins contribution to the water dynamics between hydrenchyma and chlorenchyma, typical of succulents. Therefore, the results of this study combined with future research in the area can help in understanding how climate change might affect epiphytic bromeliads, essential to the ecological balance of tropical forests.<\/p>\n Keywords:<\/strong> Bromeliaceae, nitric oxide, oxidative stress, stress memory, succulence, water deficit<\/p>\n <\/p>\n RESUMO<\/strong><\/p>\n Brom\u00e9lias ep\u00edfitas dependem da \u00e1gua da atmosfera como fonte h\u00eddrica por se sustentarem sobre \u00e1rvores e n\u00e3o haver contato direto entre suas ra\u00edzes e o solo; portanto, s\u00e3o naturalmente expostas \u00e0 seca intermitente. Plantas jovens de brom\u00e9lias ep\u00edfitas podem ser vulner\u00e1veis \u00e0 seca pois t\u00eam alta predisposi\u00e7\u00e3o \u00e0 perda de \u00e1gua e pelo fato de diversas adapta\u00e7\u00f5es morfol\u00f3gicas \u00e0 seca n\u00e3o estarem desenvolvidas por completo. A avalia\u00e7\u00e3o das respostas \u00e0 seca e reidrata\u00e7\u00e3o em plantas jovens de brom\u00e9lias pode promover maior entendimento sobre sua toler\u00e2ncia aos epis\u00f3dios de seca, que podem se intensificar devido \u00e0s altera\u00e7\u00f5es clim\u00e1ticas. Importantes componentes da defesa \u00e0 seca em plantas incluem o sistema antioxidante, o ajuste osm\u00f3tico e a regula\u00e7\u00e3o de permeabilidade de membranas atrav\u00e9s das aquaporinas. Muitas destas respostas s\u00e3o reguladas por vias de sinaliza\u00e7\u00e3o compostas por esp\u00e9cies reativas de oxig\u00eanio e nitrog\u00eanio (RNS, ROS) e o \u00e1cido absc\u00edsico (ABA), ativadas em curto prazo de exposi\u00e7\u00e3o \u00e0 seca. A brom\u00e9lia ep\u00edfita Acanthostachys strobilacea <\/em>(Schult. & Schult.f.) Klotzsch, nativa da Mata Atl\u00e2ntica e Cerrado, apresenta diversas adapta\u00e7\u00f5es \u00e0 seca (e.g.<\/em> metabolismo \u00e1cido das crassul\u00e1ceas, CAM), sendo um adequado modelo de estudo para a avalia\u00e7\u00e3o de mecanismos de defesa \u00e0 seca em plantas jovens de brom\u00e9lias ep\u00edfitas. O objetivo deste trabalho foi avaliar tr\u00eas hip\u00f3teses quanto \u00e0 resposta \u00e0 seca e recupera\u00e7\u00e3o em plantas juvenis de A. strobilacea<\/em>, sendo elas: (i) as primeiras horas de exposi\u00e7\u00e3o \u00e0 seca levam ao aumento no teor dos sinalizadores RNS, ROS e ABA e, subsequentemente, \u00e0 ativa\u00e7\u00e3o de mecanismos de defesa; (ii) as plantas mostram respostas bioqu\u00edmicas de defesa mais intensas ap\u00f3s exposi\u00e7\u00e3o a um segundo ciclo de seca-reidrata\u00e7\u00e3o, indicando forma\u00e7\u00e3o de mem\u00f3ria; (iii) existe modula\u00e7\u00e3o no ritmo diurno da fotoss\u00edntese CAM dentre a seca e reidrata\u00e7\u00e3o em curto prazo, associada a altera\u00e7\u00f5es na express\u00e3o g\u00eanica de aquaporinas, padr\u00e3o anat\u00f4mico e par\u00e2metros h\u00eddricos. Para a avalia\u00e7\u00e3o das duas primeiras hip\u00f3teses, foram quantificadas mol\u00e9culas sinalizadoras (ROS, RNS e ABA) e mecanismos de defesa bioqu\u00edmicos (e.g.<\/em> atividade antioxidante e conte\u00fado de osm\u00f3litos). Para a valida\u00e7\u00e3o da terceira hip\u00f3tese, avaliaram-se trocas gasosas, par\u00e2metros h\u00eddricos, anat\u00f4micos e express\u00e3o g\u00eanica de aquaporinas. A primeira linha de estudo mostrou que o aumento em atividade de enzimas antioxidantes, prolina e ajuste osm\u00f3tico ocorreu ao longo de 24 horas de seca concomitantemente a picos no teor de RNS, sugerindo o envolvimento destas mol\u00e9culas nas vias de sinaliza\u00e7\u00e3o \u00e0 seca. Ao contr\u00e1rio do esperado, o ac\u00famulo de ABA ocorreu posteriormente \u00e0s 72 horas de exposi\u00e7\u00e3o, estando potencialmente relacionado \u00e0 regula\u00e7\u00e3o de respostas mais tardias \u00e0 seca. O segundo estudo mostrou que o conte\u00fado de pigmentos, amino\u00e1cidos totais e atividade da S-nitrosoglutationa redutase aumentaram ap\u00f3s uma segunda exposi\u00e7\u00e3o \u00e0 seca de 14 dias, realizada ap\u00f3s um ciclo de seca de 14 dias e reidrata\u00e7\u00e3o por 5 dias, confirmando a segunda hip\u00f3tese. Por fim, a terceira hip\u00f3tese foi confirmada pois a exposi\u00e7\u00e3o \u00e0 seca e reidrata\u00e7\u00e3o por 14 dias e um dia, respectivamente, induziu de modo revers\u00edvel a remobiliza\u00e7\u00e3o de \u00e1gua no hidr\u00eanquima (tecido armazenador de \u00e1gua), ajustes na express\u00e3o g\u00eanica de aquaporinas e na fotoss\u00edntese CAM. O presente estudo fornece evid\u00eancias de mecanismos fisiol\u00f3gicos, bioqu\u00edmicos, moleculares e morfol\u00f3gicos de resist\u00eancia \u00e0 seca em plantas jovens de A. strobilacea<\/em>, demonstrando pronunciada capacidade de defesa desde est\u00e1gios ontogen\u00e9ticos iniciais nesta esp\u00e9cie. Este trabalho cria subs\u00eddios para futuros estudos sobre a resposta \u00e0 seca em ep\u00edfitas visando aprofundamento do papel das RNS e ABA em vias sinalizadoras, da forma\u00e7\u00e3o de mem\u00f3ria e da contribui\u00e7\u00e3o das aquaporinas na din\u00e2mica h\u00eddrica entre o hidr\u00eanquima e clor\u00eanquima, t\u00edpico de suculentas. <\/em>Portanto, os resultados deste trabalho aliados a futuras pesquisas na \u00e1rea podem auxiliar na compreens\u00e3o de como as altera\u00e7\u00f5es clim\u00e1ticas podem afetar brom\u00e9lias ep\u00edfitas, essenciais ao equil\u00edbrio ecol\u00f3gico das florestas tropicais.<\/p>\n Palavras-chave:<\/strong> Bromeliaceae, d\u00e9ficit h\u00eddrico, estresse oxidativo, mem\u00f3ria a estresse, \u00f3xido n\u00edtrico, sucul\u00eancia<\/p>\n![\"\"](\"https:\/\/smastr16.blob.core.windows.net\/pgibt\/sites\/242\/2023\/02\/victoria_carvalho_dr.jpg\")
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\nToler\u00e2ncia e mem\u00f3ria \u00e0 seca na brom\u00e9lia ep\u00edfita Acanthostachys strobilacea<\/em> (Schult. & Schult.f.) Klotzsch<\/strong><\/h3>\n
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<\/a>Victoria de Carvalho<\/a>
\nToler\u00e2ncia e mem\u00f3ria \u00e0 seca na brom\u00e9lia ep\u00edfita Acanthostachys strobilacea<\/em> (Schult. & Schult.f.) Klotzsch<\/a><\/p>\n
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