c6.6.5 – Gas exchange and antioxidants in Fraxinus excelsior trees with ozone visible injury and infused with the antiozonant edu

Paoletti E* (1), Contran N (2), Castagna A (3), Ranieri A (3), Tagliaferro F (4), Manning WJ (5)

(1) IPP-CNR, Sesto Fiorentino (FI); (2) Dip. Scienze Ambientali Univ. Milano-Bicocca, Milano; (3) Dip. Chimica Agricola e Biotecnologie, Univ. Pisa, Pisa; (4) IPLA, Torino; (5) Dept. Plant, Soil and Insect Sciences, Univ. Massachusetts, Amherst MA, USA
Collocazione: c6.6.5 – Tipo Comunicazione: Poster
6° Congresso SISEF *
Sessione 6: “Poster: “Fattori di stress e strategie di mitigazione”” *

Contatto: Elena Paoletti (e.paoletti@ipp.cnr.it)

Abstract: Much has been written about the effects of ozone on growth of forest trees, but conclusive proof that ambient levels of O3 affect growth of forest trees remains elusive, usually because the experimental techniques do not allow extrapolation to realistic conditions. Ethylenediurea (EDU), used as a foliar spray or soil/potting medium drench, is systemic and persistent in plants, and has been used to prevent foliar O3 injury and determine O3 effects on growth and yield of many herbaceous plants and some woody plants. Gravitational trunk infusion of EDU has been demonstrated to prevent foliar O3 injury on sensitive ash (Fraxinus excelsior L.) trees. We report here additional results from the same field experiment where adult trees were gravitationally infused with EDU to determine effects on gas exchange and apoplastic antioxidants. Ash trees were considered to be either sensitive or insensitive to ozone, as determined by presence or absence of foliar symptoms in previous years. They were treated with EDU at 450 ppm by gravitational trunk infusion at 3-week intervals over May-September 2005 (32.5 ppm h AOT40). In September, gas exchange, assimilation curves and a number of biochemical parameters were measured. Neither EDU nor tree visible injury affected carbon assimilation and stomatal conductance. However, the infusion of EDU maintained the tight coupling of the relationship between carbon assimilation and stomatal conductance, while the water-infused trees showed an uncoupling. This is suggested to be a protective effect of EDU against ambient exposure to elevated ozone. An uncoupling between carbon assimilation and stomatal conductance has been reported as ozone response in several species. Apoplastic antioxidant capacity was evaluated by measuring ascorbate (ASA) and ascorbate plus dehydroascorbate (TOT) levels and redox state (ASA/TOT) as well as ascorbate peroxidase (APX) activity. Total ascorbate content was lower in EDU-infused trees. However, in ozone-sensitive trees, the redox state was higher than in water-infused trees, despite an enhanced APX activity, suggesting stimulation of intracellular dehydroascorbate reduction. These contrasting results suggest that ascorbate does not play an important role in EDU-induced protection against ozone injury. In conclusion, gravitational infusion was demonstrated a useful tool to investigate the mechanisms of EDU protection and ozone effects on adult trees under ambient conditions.

Citazione: Paoletti E , Contran N , Castagna A , Ranieri A , Tagliaferro F , Manning WJ (2007). Gas exchange and antioxidants in Fraxinus excelsior trees with ozone visible injury and infused with the antiozonant edu . 6° Congresso Nazionale SISEF, Arezzo, 25 – 27 Set 2007, Contributo no. #c6.6.5