Responses of eucalypt species to aluminum: the possible involvement of low molecular weight organic acids in the Al tolerance mechanism

Abstract

Aluminum (Al) tolerance mechanisms in crop plants have been extensively researched, but our understanding of the physiological mechanisms underlying Al tolerance in trees is still limited. To investigate Al tolerance in eucalypts, seedlings of six species (Eucalyptus globulus Labill., Eucalyptus urophylla S.T. Blake, Eucalyptus dunnii Maiden, Eucalyptus saligna Sm., Eucalyptus cloeziana F. J. Muell. and Eucalyptus grandis w. Hill ex Maiden) and seedlings of six clones of Eucalyptus species were grown for 10 days in nutrient solutions containing Al concentrations varying from 0 to 2.5 microM (0 to 648 microM Al3+ activities). Root elongation of most species was inhibited only by high Al3+ activities. Low to intermediate Al3+ activities were beneficial to root elongation of all species and clones. Among the species tested, E. globulus and E. urophylla were more tolerant to Al toxicity, whereas E. grandis and E. cloeziana were more susceptible to Al-induced damage. Although E. globulus seedlings were tolerant to Al toxicity, they were highly sensitive to lanthanum (La), indicating that the tolerance mechanism is specific for Al. Fine roots accumulated more Al and their elongation was inhibited more than that of thick roots. In E. globulus, accumulation of Al in root tips increased linearly with increasing Al concentration in the nutrient solution. The majority of Al taken up was retained in the root system, and the small amounts of Al translocated to the shoot system were found mainly in older leaves. No more than 60% of the Al in the thick root tip was in an exchangeable form in the apoplast that could be removed by sequential citrate rinses. Gas chromatography/mass spectrometry and ion chromatography analyses indicated that root exposure to Al led to a greater than 200% increase in malic acid concentration in the root tips of all eucalypt species. The increase in malate concentration in response to Al treatment correlated with the degree of Al tolerance of the species. A small increase in citric acid concentration was also observed in all species, but there were no consistent changes in the concentrations of other organic acids in response to Al treatment. In all eucalypt species, Al treatment induced the secretion of citric and malic acid in root exudates, but no trend with respect to Al tolerance was observed. Thus, although malate and citrate exudation by roots may partially account for the overall high Al tolerance of these eucalypt species, it appears that tolerance is mainly derived from the internal detoxification of Al by complexation with malic acid.

Intra-specific variation in response of Neem (Azadirachta indica A. Juss) to elevated CO2 levels and biochemical characterization of differently responding plants

“…However, there is not much difference among clones in respect of Citric acid content (Table 3). Similar variation in organic acid contents under exposure to stress environments has been reported by Silva et al (2004) who reported that Gas chromatography/mass spectrometry and ion chromatography analyses indicated that root exposure to AI led to a greater than 200% increase in Malic acid concentration in the root tips of all eucalypt species. The increase in Malate concentration in response to AI treatment is correlated with the tree species.…”

Alterations of soil chemical properties by eucalyptus cultivation in five regions in the Rio Doce Valley

“…However, liming was not a common practice until recently because eucalyptus plants are highly Altolerant (Neves et al, 1982a;Vale et al, 1984;Silva et al, 2002Silva et al, , 2004 and grow well in acid soils with relatively low Ca content (Neves et al, 1982b;. This may have added to further reduce the Ca and Mg contents of these soils.…”

“…This suggests, among other aspects, that the soil under eucalyptus might be a less favorable environment for fine-root growth (Khanna & Ulrich, 1984) than previously under pasture. Although eucalyptus is known to be an Al-tolerant species, fineroot growth may be restricted by high Al 3+ activities (Silva et al, 2004), especially under conditions of low Ca 2+ availability. This could undermine water and nutrient uptake and eventually reduce tree growth because eucalyptus biomass yield seems to be related to fine-root growth (diameter ≤ 3.0 mm) (Gatto et al, 2003).…”

BIOMASSA E NUTRIENTES EM POVOAMENTO DE Eucalyptus dunnii Maiden NO PAMPA GAÚCHO1

“…As espécies do gênero Eucalyptus apresentam tolerância a altas concentrações de alumínio na solução do solo (SILVA et al, 2004;POSCHENRIEDER et al, 2008;TAHARA et al, 2008), à baixa fertilidade natural e a níveis de cálcio e magnésio inferiores aos estabelecidos como críticos para a maioria das culturas (BARROS; NOVAIS, 1990;RIBEIRO et al, 1999). Os mecanismos de tolerância ao Al são vários, podendo ser fisiológicos (SILVA et al, 2004;POSCHENRIEDER et al, 2008) e, ou, indiretos, pela complexação do Al pela fração orgânica (VIEIRA, et al, 2008).…”

“…Os mecanismos de tolerância ao Al são vários, podendo ser fisiológicos (SILVA et al, 2004;POSCHENRIEDER et al, 2008) e, ou, indiretos, pela complexação do Al pela fração orgânica (VIEIRA, et al, 2008).…”