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Open AccessArticle

The Apoplastic and Symplastic Antioxidant System in Onion: Response to Long-Term Salt Stress

1
Departamento de Ciencias Biológicas, Decanato de Agronomía, Universidad Centroccidental Lisandro Alvarado UCLA, Barquisimeto 3001, Estado Lara, Venezuela
2
Grupo de Biotecnología de Frutales, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), 30100 Murcia, Spain
3
Facultad de Ingeniería Agronómica, Universidad Técnica de Manabí. Portoviejo, Manabí 130105, Ecuador
4
Instituto de Botánica Agrícola, Facultad de Agronomía, Universidad Central de Venezuela, Av. 19 de abril, Maracay 1050, Estado Aragua, Venezuela
*
Author to whom correspondence should be addressed.
Antioxidants 2020, 9(1), 67; https://doi.org/10.3390/antiox9010067
Received: 12 December 2019 / Revised: 7 January 2020 / Accepted: 9 January 2020 / Published: 12 January 2020
(This article belongs to the Special Issue Extracellular Antioxidant Systems in Plants)
The response of apoplastic antioxidant systems in root and leaf tissues from two onion genotypes (‘Texas 502’, salt-sensitive and ‘Granex 429’, salt-resistant) in response to salinity was studied. Electrolyte leakage data indicated the membrane integrity impairing by the effect of salts, especially in ‘Texas 502’. We detected superoxide dismutase (SOD) and peroxidase (POX) activity in the root and leaf apoplastic fractions from onion plants. Salinity increased SOD activity in the root symplast of ‘Texas 502’ and in ‘Granex 429’ leaves. In contrast, salinity reduced SOD activity in the leaf and root apoplastic fractions from ‘Texas 502’. In ‘Granex 429’, salt-stress increased leaf apoplastic POX activity and symplastic catalase (CAT) activity of both organs, but a decline in root apoplastic POX from ‘Texas 502’ took place. Salt-stress increased monodehydroascorbate reductase (MDHAR) in root and leaf symplast and in root glutathione reductase GR, mainly in ‘Granex 429’, but only in this genotype, leaf dehydroascorbate reductase (DHAR) activity increased. In contrast, a decline in leaf GR was produced only in ‘Texas 502’. Salinity increased leaf ASC levels, and no accumulation of dehydroascorbate (DHA) was observed in roots in both cases. These responses increased the redox state of ascorbate, especially in roots. In contrast, salinity declined reduced glutathione (GSH), but oxidised glutathione (GSSG) was accumulated in leaves, decreasing the redox state of glutathione. Salinity slightly increased root GSH concentration in the salt-tolerant genotype and was unchanged in the salt-sensitive genotype, but no accumulation of GSSG was produced, favoring the rise and/or maintenance of the redox state of the glutathione. These results suggest that the lower sensitivity to salt in ‘Granex 429’ could be related to a better performance of the antioxidant machinery under salinity conditions. View Full-Text
Keywords: Allium cepa; antioxidant defenses; apoplast; extracellular antioxidants; oxidative damage; salinity; symplast Allium cepa; antioxidant defenses; apoplast; extracellular antioxidants; oxidative damage; salinity; symplast
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García, G.; Clemente-Moreno, M.J.; Díaz-Vivancos, P.; García, M.; Hernández, J.A. The Apoplastic and Symplastic Antioxidant System in Onion: Response to Long-Term Salt Stress. Antioxidants 2020, 9, 67.

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