RESUMEN

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.

RESUMEN

A ocorrência de alumínio (Al) em concentrações tóxicas no solo é considerada como a principal causa da baixa fertilidade dos solos do cerrado no Brasil, visto que o Al é um constituinte das partículas de argila do solo. O efeito negativo da acidez do solo e da toxidez por Al na produção agrícola tem sido menos frequente em sistema de plantio direto, com ausência de resposta das culturas tanto à calagem quanto a gessagem, fato relacionado à complexação de Al pelos ácidos orgânicos. Os mecanismos de tolerância internos são aqueles em que o Al entra no simplasto e a tolerância é encontrada pela formação de quelatos no citossol, compartimentalização no vacúolo, ligação do alumínio a proteínas e atuação de enzimas tolerantes ao Al. A tolerância ao Al é geneticamente controlada e as espécies de plantas diferem significativamente quanto ao grau dessa tolerância. Devido à complexidade da fitotoxicidade do Al e dos mecanismos de tolerância apresentados pelas plantas há necessidade de investigação científica mais aprofundada para a obtenção de cultivares tolerantes, com o intuito de elevar a produtividade dos solos com presença de Al.

The occurrence of toxic Al concentrations in the soil is considered the main cause of low fertility of cerrado soils in Brazil, since as the Al is a component of soil clay particules. The negative effect of soil acidity and Al toxicity in agricultural production has been less common in no tillage, and observed the lack of crop response to liming as much as the gypsum, being related to complexation of Al with organic acids. The internal tolerance mechanisms are those in which Al enters the symplast and tolerance is found for the formation of chelates in the cytosol, compartmentalization in the vacuole, aluminum bound to proteins and evolution of Al-tolerant enzymes. The tolerance to Al is genetically controlled and plant species differ significantly in the degree of tolerance. Due to the complexity of Al phytotoxicity and tolerance mechanisms displayed by plants, further scientific research is desired for obtaining tolerant cultivars to raise the productivity of soils with Al.

Asunto(s)

RESUMEN

A ocorrência de alumínio (Al) em concentrações tóxicas no solo é considerada como a principal causa da baixa fertilidade dos solos do cerrado no Brasil, visto que o Al é um constituinte das partículas de argila do solo. O efeito negativo da acidez do solo e da toxidez por Al na produção agrícola tem sido menos frequente em sistema de plantio direto, com ausência de resposta das culturas tanto à calagem quanto a gessagem, fato relacionado à complexação de Al pelos ácidos orgânicos. Os mecanismos de tolerância internos são aqueles em que o Al entra no simplasto e a tolerância é encontrada pela formação de quelatos no citossol, compartimentalização no vacúolo, ligação do alumínio a proteínas e atuação de enzimas tolerantes ao Al. A tolerância ao Al é geneticamente controlada e as espécies de plantas diferem significativamente quanto ao grau dessa tolerância. Devido à complexidade da fitotoxicidade do Al e dos mecanismos de tolerância apresentados pelas plantas há necessidade de investigação científica mais aprofundada para a obtenção de cultivares tolerantes, com o intuito de elevar a produtividade dos solos com presença de Al.(AU)

The occurrence of toxic Al concentrations in the soil is considered the main cause of low fertility of cerrado soils in Brazil, since as the Al is a component of soil clay particules. The negative effect of soil acidity and Al toxicity in agricultural production has been less common in no tillage, and observed the lack of crop response to liming as much as the gypsum, being related to complexation of Al with organic acids. The internal tolerance mechanisms are those in which Al enters the symplast and tolerance is found for the formation of chelates in the cytosol, compartmentalization in the vacuole, aluminum bound to proteins and evolution of Al-tolerant enzymes. The tolerance to Al is genetically controlled and plant species differ significantly in the degree of tolerance. Due to the complexity of Al phytotoxicity and tolerance mechanisms displayed by plants, further scientific research is desired for obtaining tolerant cultivars to raise the productivity of soils with Al.(AU)

Asunto(s)