Tree Physiology Advance Access originally published online on July 16, 2009
Tree Physiology 2009 29(9):1187-1198; doi:10.1093/treephys/tpp047
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Antioxidant defences and oxidative damage in salt-treated olive plants under contrasting sunlight irradiance
1 Departamento de Agronomia, Universidad de Córdoba, Edificio ‘Celestino Mutis’, Campus Universitario de Rabanales, 14071 Córdoba, Spain
2 Dipartimento di Difesa e Coltivazione delle Specie Legnose ‘G. Scaramuzzi’, Università di Pisa, I-56124 Pisa, Italy
3 Dipartimento di Chimica e Biotecnologie Agrarie, Università di Pisa, I-56124 Pisa, Italy
4 IFAC, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019 Sesto F.no, Firenze, Italy
5 IBBA, Consiglio Nazionale delle Ricerche, Via Bassini 15, I-20100 Milano, Italy
6 Dipartimento di Chimica, Università di Siena, Via A. Moro 2, I-53100 Siena, Italy
7 ISE, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019 Sesto F.no, Firenze, Italy
8 IVALSA, Consiglio Nazionale delle Ricerche, Via Madonna del Piano 10, I-50019 Sesto F.no, Firenze, Italy
9 Corresponding author (m.tattini{at}ivalsa.cnr.it)
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Abstract |
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The interactive effects of root-zone salinity and sunlight on leaf biochemistry, with special emphasis on antioxidant defences, were analysed in Olea europaea L. cv. Allora, during the summer period. Plants were grown outside under 15% (shade plants) or 100% sunlight (sun plants) and supplied with 0 or 125 mM NaCl. The following measurements were performed: (1) the contribution of ions and soluble carbohydrates to osmotic potentials; (2) the photosystem II (PSII) photochemistry and the photosynthetic pigment concentration; (3) the concentration and the tissue-specific distribution of leaf flavonoids; (4) the activity of antioxidant enzymes; and (5) the leaf oxidative damage. The concentrations of Na+ and Cl– were significantly greater in sun than in shade leaves, as also observed for the concentration of the ‘antioxidant’ sugar–alcohol mannitol. The de-epoxidation state of violaxanthin-cycle pigments increased in response to salinity stress in sun leaves. This finding agrees with a greater maximal PSII photochemistry (Fv/Fm) at midday, detected in salt-treated than in control plants, growing in full sunshine. By contrast, salt-treated plants in the shade suffered from midday depression in Fv/Fm to a greater degree than that observed in control plants. The high concentration of violaxanthin-cycle pigments in sun leaves suggests that zeaxanthin may protect the chloroplast from photo-oxidative damage, rather than dissipating excess excitation energy via non-photochemical quenching mechanisms. Dihydroxy B-ring-substituted flavonoid glycosides accumulate greatly in the mesophyll, not only in the epidermal cells, in response to high sunlight. The activity of antioxidant enzymes varied little because of sunlight irradiance, but declined sharply in response to high salinity in shade leaves. Interestingly, control and particularly salt-treated plants in the shade underwent greater oxidative damage than their sunny counterparts. These findings, which conform to the evolution of O. europaea in sunny environments, suggest that under partial shading, the antioxidant defence system may be ineffective to counter salt-induced oxidative damage.
Keywords: antioxidant enzymes, chlorophyll fluorescence, electron paramagnetic resonance, flavonoid glycosides, fluorescence microspectroscopy, mannitol, violaxanthin-cycle pigments
Received February 19, 2009; Accepted June 11, 2009