Respostas fisiológicas envolvidas na tolerância à restrição hídrica e estresse luminoso em Orchidaceae epífitas
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2020-02-21
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Universidade Estadual Paulista (Unesp)
Resumo
Orquídeas epífitas estão expostas a diferentes microclimas, que são caracterizados pela alta irradiância imposta ao dossel e baixa irradiância em plantas situadas no sub-bosque. Além disso, este grupo de plantas frequentemente lida com a restrição hídrica. Na produção comercial, o estabelecimento de orquídeas é em quase sua totalidade limitada pela distribuição e intensidade destes mesmos fatores disponibilizados em casas de vegetação. Gomesa flexuosa Sims e Oncidium sphacelatum Lindley pertencem à subtribo Oncidiinae, e quando hibridizadas dão origem a O. ‘Aloha’ (uma orquídea CAM facultativa e importante híbrida comercial). O objetivo deste estudo foi elucidar a performance fotossintética e as estratégias de balanço hídrico de G. flexuosa e O. sphacelatum sob condições de estresse hídrico e luminoso, focando tanto nas diferenças interespecíficas como nas funções dos diferentes órgãos em um mesmo indivíduo. Para isso, analisamos trocas gasosas, fluorescência da clorofila a, quantificação de lipoperóxidos, discriminação isotópica, acidez titulável, conteúdo relativo de água e potencial hídrico em tecidos foliares, de pseudobulbos e raízes, em diferentes tratamentos envolvendo restrição hídrica e variação luminosa. Depois de restrição hídrica por 60 dias, G. flexuosa apresentou conversão de metabolismo C3 para CAM, o que deu subsídios para uma melhor performance das trocas gasosas, fluorescência da clorofila a, mecanismo de fotoproteção e relações hídricas. Quando submetida a dois eventos de restrição hídrica, mostrou capacidade de armazenar informações de experiência prévias, apresentando memória fisiológica. Ao avaliar como a restrição hídrica somada ao estresse luminoso influencia nas respostas fisiológicas de ambas as espécies por 180 dias, mais uma vez G. flexuosa apresentou melhor performance e possibilidade de rustificação pela luz, enquanto O. sphacelatum não se rustificou e não apresentou memória fisiológica. Estes dados podem contribuir para programas de conservação de espécies nativas, além de nortear estratégias de cultivo para fins comerciais.
Epiphyte orchids are exposed to different microclimates, which are characterized by high irradiance imposed on the canopy and low irradiance in plants located on the understory. In addition, this group of plants frequently deals with water restriction. In commercial production, the distribution and intensity of these same factors inside the greenhouses also limit the orchids establishment. Gomesa flexuosa Sims and Oncidium sphacelatum Lindley are Oncidiinae species and when hybridized, it gave origin to O. ‘Aloha’ (a facultative CAM orchid and na important commercial hybrid). The aim of this study was to elucidate the photosynthetic performance and the water balance strategies of G. flexuosa and O. sphacelatum under water and light stress conditions, focusing on an interspecific diferences as well as on different organs functions in the same individual. For that, we analyzed the gas exchange, chlorophyll a fluorescence, lipoperoxides quantification, isotopic discrimination, titratable acidity, water relative content and water potential of leaf, pseudobulb and root tissues in different treatments involving water restriction and light variation. After 60 days of water restriction, G. flexuosa converted the photosynthetic metabolism from C3 to CAM, which provided a better performance on gas exchanges, chlorophyll a fluorescence, photoprotection mechanism and water relations. When G. flexuosa was submitted to two events of water restriction, it showed a capacity to store information from previous stress experiences, demonstrating physiological memory. When evaluating how water restriction added to light stress influences the physiological responses of both species for 180 days, G. flexuosa again showed better performance and light rusting possibility, while O. sphacelatum did not rust and did not show physiological memory. Our results can contribute to conservation programs of native orchids species as well to guide cultivation strategies for commercial purposes.
Epiphyte orchids are exposed to different microclimates, which are characterized by high irradiance imposed on the canopy and low irradiance in plants located on the understory. In addition, this group of plants frequently deals with water restriction. In commercial production, the distribution and intensity of these same factors inside the greenhouses also limit the orchids establishment. Gomesa flexuosa Sims and Oncidium sphacelatum Lindley are Oncidiinae species and when hybridized, it gave origin to O. ‘Aloha’ (a facultative CAM orchid and na important commercial hybrid). The aim of this study was to elucidate the photosynthetic performance and the water balance strategies of G. flexuosa and O. sphacelatum under water and light stress conditions, focusing on an interspecific diferences as well as on different organs functions in the same individual. For that, we analyzed the gas exchange, chlorophyll a fluorescence, lipoperoxides quantification, isotopic discrimination, titratable acidity, water relative content and water potential of leaf, pseudobulb and root tissues in different treatments involving water restriction and light variation. After 60 days of water restriction, G. flexuosa converted the photosynthetic metabolism from C3 to CAM, which provided a better performance on gas exchanges, chlorophyll a fluorescence, photoprotection mechanism and water relations. When G. flexuosa was submitted to two events of water restriction, it showed a capacity to store information from previous stress experiences, demonstrating physiological memory. When evaluating how water restriction added to light stress influences the physiological responses of both species for 180 days, G. flexuosa again showed better performance and light rusting possibility, while O. sphacelatum did not rust and did not show physiological memory. Our results can contribute to conservation programs of native orchids species as well to guide cultivation strategies for commercial purposes.
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Orquídea, Balanço hidrológico, Fotossíntese, Desidratação (hídrica), Plantas, Efeito da luz, Orchid, Hydrological balance, Photosynthesis, Dehydration (water), Plants, Light effect