Análise fisiológica e molecular em Rhizophora mangle: respostas ao estresse salino em condições de campo
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Data
2019-09-24
Autores
Lopes, Dielle Meire de Santana
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Universidade Federal do Espírito Santo
Resumo
The mangrove ecosystem is highly productive, however, it is constantly subject to environmental stressors, which include salinity and elevated temperatures. The aim of the present study was to investigate the physiological and molecular bases of salt tolerance in Rhizophora mangle using the techniques of chlorophyll a fluorescence analysis, gas exchange, chlorophyll a index and gene expression by qRT-PCR. The study was carried out in two mangrove forests in the São Mateus River Estuary, in the HS area of higher salinity and in the LS area of lower salinity. Mangrove forest in the LS area is in a recolonization stage, a process evaluated as natural, with replacement of mature plants by recent stages of development. The HS area was characterized as having a higher degree of structural development and dominated by mature R. mangle individuals. The salinity values showed differences between the areas in all samplings being always higher in HS. The rate of assimilation of CO2 (A), stomatal conductance (gs), leaf transpiration (E), intrinsic efficiency of water use (A/gs) and chlorophyll a, L-band, IP-phase, and performance index (PITOTAL) were in the higher values in LS area. The instantaneous water use efficiency (A/ E), initial fluorescence (F0), maximum fluorescence (Fm), and J-step were higher in HS. Photosynthetic maintenance under conditions of high salinity was supported by improved activity of photosystem II (PSII), including the increase of active reaction centers (RCs) and oxygen evolution complexes (CEOs). The psbA (D1 protein of the RC) and PSBO2 (subunit of the OEC) genes were up-regulated under high salinity, which may be related to an increased efficiency to repair injuries in the RC and OEC through synthesis of new subunits, improving the PSII activity. In addition, the expression of other five genes involved in ATP synthesis, RubisCO activation, ROS scavenging, GABA synthesis and vacuolar Na+ sequestration were up-regulated under high salinity. Plants of R. mangle present mechanisms that tolerate salinity increase, and this is evaluated by the responses of the plants of the HS area where they exhibited a greater number of active RCs, greater photochemical activity, as well as, better energy connectivity between the antennas and the RCs of the PSII and better efficiency in electron transfer between the CEO and the accepting side of PSII. However, higher values of PITOTAL and IP phase in LS plants indicate a better efficiency of the reduction of PSI final acceptors, which suggests higher PSI activity. The saline variation along the samplings in the LS area tends to influence the transport of electrons in plants of R. mangle and consequently, to damage the structural development of the adult forest. Thus, our data shed light on the salt tolerance mechanism and provide specific genes regulated by salt in R. mangle under field conditions
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Rhizophora mangle , Fluorescência da clorofila a , Trocas gasosas , Pigmentos foliares , Expressão gênica , Chlorophyll a fluorescence , Gas exchange , Leaf pigments , Gene expression