After fire, holm oak (Quercus ilex L.) resprouts have a higher light availability and photosynthetic activity than control plants in intact vegetation. To assess the differences in protection between these plants, we determined, in two forests, changes in gas-exchange rates, chlorophyll fluorescence parameters, chloroplast pigment content and total antioxidant activity (TAA) in different seasons, at different times of the day and in relation to leaf age. The end-point method used for TAA determination allowed the evaluation of the relative contribution of hydrophilic and lipophilic antioxidants in leaf extracts. High correlations were obtained between lipophilic TAA and certain chloroplast pigment content, the highest contribution being provided by β-carotene and the components of the xanthophyll cycle (zeaxanthin + antheraxanthin, violaxanthin). All leaves showed a much higher contribution (94-99%) of hydrophilic than lipophilic antioxidants to TAA. In summer, at midday, photosynthetic rates and TAA were higher in resprouts. In these plants, reduced xanthophyll-cycle participation (as shown by non-photochemical quenching (NPQ) and xanthophyll pool content) was compensated by an increased participation of hydrophilic antioxidants. No effect of time of day or plant age was observed. The results suggest that energy dissipation as heat, and detoxification mechanisms contribute to the protective strategies of control plants and resprouts, albeit to a different extent.

This research was supported by funds from DGICYT PB98-1198-C02-01, from Generalitat de Catalunya 1999 SGR0020 and from MCT-INIA (Spain) project CAL00-062. We thank the Servei de Meteorologia, Departament de Medi Ambient, of the Generalitat de Catalunya for the climatological data, the Patronat del Parc de Collserola for use of its facilities and Robin Rycroft (Servei d'Assesorament Lingüístic, Escola d'Idiomes Moderns, UB) for correcting the English manuscript. A. Cano was the recipient of a grant from the Fundación Séneca (C.A. Murcia, Spain).

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