Ozone symptoms in leaves of woody plants in open‐top chambers: ultrastructural and physiological characteristics

Abstract

This study was carried out in the summer of 2001 at the Lattecaldo open‐top chamber research facility (Canton Ticino, southern Switzerland). The aim of this research study was to examine the behaviour of Fraxinus excelsior, Prunus avium and Viburnum lantana seedlings grown in charcoal‐filtered (CF) (∼ 50% of the ambient O3) and non‐filtered (NF) (∼ 92% of the ambient O3) air open‐top chambers. Investigations included the assessment of visible foliar symptom development, anatomical and ultrastructural analysis of symptoms, measurements of direct chlorophyll a fluorescence (fluorescence findings were processed by means of the JIP test) and leaf gas exchange measurements. The three species displayed different foliar symptoms. In F. excelsior, symptoms consisted of punctiform stipples with necrotic cells (hypersensitive response, HR), whereas, in P. avium and V. lantana, reddening developed, revealing the accumulation of anthocyanins. In V. lantana, symptoms appeared earlier than in the other species; in F. excelsior, symptoms developed more rapidly and led to premature leaf abscission. In F. excelsior, at least at the beginning, the onset of symptoms was combined with an enhanced photosynthetic efficiency (compensation mechanism), whereas, in P. avium and V. lantana, this efficiency progressively decreased. The fluorescence parameters most closely connected to ozone stress were as follows: a reduction in performance index (PIABS) and active reaction centres (RC/CS0), and an increase in the variable fluorescence relative to 30 ms (VI) and of the dissipation processes. Dissipation is a form of defence mechanism against oxidative stress and is related to the role of the deactivated reaction centres (the silent centres) as well as anthocyanins. Symptom development correlated in all three species with the reduction in reaction centres. Symptomatic leaves had a lower net photosynthetic rate (Pn). Net photosynthesis correlated with the reduction in VI, which suggests an accumulation of reduced plastoquinone, produced in the luminous phase of photosynthesis, which was not capable of reaching the dark phase reactions.

Structural changes in Psidium guajava 'Paluma' leaves exposed to tropospheric ozone

“…Besides the direct action of the antioxidant, anthocyanins protect the chloroplasts from excess excitation by activating a controlled energy dissipation process and, hence, the potential for oxidative damage (Gravano et al 2004). Comparative values of stomata density between plants of Psidium guajava 'Paluma' exposed to the environment and those kept inside the greenhouse with fi ltered air.…”

Atmospheric Deposition and Ozone Levels in Swiss Forests: Are Critical Values Exceeded?

“…Uptake of O 3 at ambient concentrations through the stomata and the related accumulation of reactive oxygen species within plant leaves can cause the collapse of parenchym cells leading to decreased rates of photosynthesis and plant growth (Kärenlampi and Skärby 1996). Ozone-induced injuries present a wide range of visible symptoms (e.g., Gravano et al 2004;Innes et al 1996Innes et al , 2001Novak et al 2003).…”

Interactive effects of elevated ozone and springtime frost on growth and physiology of birch (Betula pendula) in field conditions

“…However, the leaves that were used for photosynthesis and fluorescence measurements in our study had little symptomatic dots, since they were chosen from the middle of the canopy, and it has been shown that during the early stages of the ozone injury photosynthetic efficiency may also be stimulated owing to the activation of metabolic responses to compensate for the reduced number of photosynthetically active cells (Gravano et al 2004).…”