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Int J Mol Sci ; 22(16)2021 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-34445145


The main goal of growing plants under various photoperiods is to optimize photosynthesis for using the effect of day length that often acts on plants in combination with biotic and/or abiotic stresses. In this study, Brassica juncea plants were grown under four different day-length regimes, namely., 8 h day/16 h night, 12 h day/12 h night, 16 h day/8 h night, and continuous light, and were infected with a necrotrophic fungus Alternaria brassicicola. The development of necroses on B. juncea leaves was strongly influenced by leaf position and day length. The largest necroses were formed on plants grown under a 16 h day/8 h night photoperiod at 72 h post-inoculation (hpi). The implemented day-length regimes had a great impact on leaf morphology in response to A. brassicicola infection. They also influenced the chlorophyll and carotenoid contents and photosynthesis efficiency. Both the 1st (the oldest) and 3rd infected leaves showed significantly higher minimal fluorescence (F0) compared to the control leaves. Significantly lower values of other investigated chlorophyll a fluorescence parameters, e.g., maximum quantum yield of photosystem II (Fv/Fm) and non-photochemical quenching (NPQ), were observed in both infected leaves compared to the control, especially at 72 hpi. The oldest infected leaf, of approximately 30% of the B. juncea plants, grown under long-day and continuous light conditions showed a 'green island' phenotype in the form of a green ring surrounding an area of necrosis at 48 hpi. This phenomenon was also reflected in changes in the chloroplast's ultrastructure and accelerated senescence (yellowing) in the form of expanding chlorosis. Further research should investigate the mechanism and physiological aspects of 'green islands' formation in this pathosystem.

Alternaria/patogenicidade , Mostardeira/microbiologia , Mostardeira/fisiologia , Necrose/microbiologia , Necrose/patologia , Fotossíntese/fisiologia , Doenças das Plantas/microbiologia , Carotenoides/metabolismo , Clorofila/metabolismo , Clorofila A/metabolismo , Fluorescência , Mostardeira/metabolismo , Necrose/metabolismo , Fotoperíodo , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/metabolismo , Folhas de Planta/microbiologia
Cells ; 9(10)2020 10 20.
Artigo em Inglês | MEDLINE | ID: mdl-33092216


Black spot disease, caused by Alternaria brassicicola in Brassica species, is one of the most devastating diseases all over the world, especially since there is no known fully resistant Brassica cultivar. In this study, the visualization of black spot disease development on Brassica oleracea var. capitata f. alba (white cabbage) leaves and subsequent ultrastructural, molecular and physiological investigations were conducted. Inter- and intracellular hyphae growth within leaf tissues led to the loss of host cell integrity and various levels of organelle disintegration. Severe symptoms of chloroplast damage included the degeneration of chloroplast envelope and grana, and the loss of electron denseness by stroma at the advanced stage of infection. Transcriptional profiling of infected leaves revealed that photosynthesis was the most negatively regulated biological process. However, in infected leaves, chlorophyll and carotenoid content did not decrease until 48 hpi, and several chlorophyll a fluorescence parameters, such as photosystem II quantum yield (Fv/Fm), non-photochemical quenching (NPQ), or plant vitality parameter (Rdf) decreased significantly at 24 and 48 hpi compared to control leaves. Our results indicate that the initial stages of interaction between B. oleracea and A. brassicicola are not uniform within an inoculation site and show a complexity of host responses and fungal attempts to overcome host cell defense mechanisms. The downregulation of photosynthesis at the early stage of this susceptible interaction suggests that it may be a part of a host defense strategy, or, alternatively, that chloroplasts are targets for the unknown virulence factor(s) of A. brassicicola. However, the observed decrease of photosynthetic efficiency at the later stages of infection is a result of the fungus-induced necrotic lesion expansion.

Alternaria/ultraestrutura , Brassica/genética , Brassica/microbiologia , Regulação para Baixo , Interações Hospedeiro-Patógeno/genética , Fotossíntese , Doenças das Plantas/microbiologia , Transcrição Genética , Alternaria/fisiologia , Brassica/fisiologia , Brassica/ultraestrutura , Clorofila A/metabolismo , Cloroplastos/metabolismo , Cloroplastos/ultraestrutura , Suscetibilidade a Doenças , Regulação da Expressão Gênica de Plantas , Ontologia Genética , Células do Mesofilo/microbiologia , Células do Mesofilo/ultraestrutura , Fotossíntese/genética , Folhas de Planta/microbiologia , Folhas de Planta/ultraestrutura , Fatores de Tempo