biologia plantarum

Biologia plantarum 49:585-592, 2005 | DOI: 10.1007/s10535-005-0053-2

Cell death behind invisible symptoms: early diagnosis of ozone injury

F. Faoro^1,*, M. Iriti¹

¹ Istituto di Virologia Vegetale, CNR, Sezione di Milano and Istituto di Patologia Vegetale, Universita di Milano, Milano, Italy

A simple histo-cytochemical method, combining Evans blue staining to assess cell death and in vivo 3,3'-diaminobenzidine uptake for H₂O₂ localisation, has been used to evaluate O₃ damages in leaf tissues of three Phaseolus vulgaris L. cultivars (Cannellino, BLF, Saxa) with different sensitivity to the pollutant. Bean plants were exposed to a single pulse of O₃ (150 ± 10 mm³ m^-3 × 3 h) and leaves were examined at different time-span after fumigation. Cannellino proved to be the most sensitive, showing chlorotic spots 2 h after fumigation and chlorotic lesions 24 h later. In BLF, necrotic spots appeared 4 h after fumigation and reddish necrotic lesions (bronzing) developed in further 24 h. Saxa remained symptomless up to 10 d of observation, thus appearing tolerant. The early appearance of symptoms in Cannellino correlated with H₂O₂ accumulation in leaf tissues and consequent extensive cell death, involving both palisade and spongy mesophyll. H₂O₂ accumulation was observed also in BLF, though to a lesser extent and dead cells were rare at 2 h after fumigation. However, they increased in number 24 h later, forming small groups in the palisade mesophyll. These groups further enlarged in the next 24 h, again involving only palisade mesophyll. In Saxa leaves, H₂O₂ accumulation was found only in the epidermal cells, though the number of dead cells was very similar to BLF, at least up to 24 h after fumigation. However, in Saxa, dead cells have been always found singly scattered through the palisade mesophyll, or forming very small groups around substomatal cavity, thus remaining invisible at a macroscopic level.

Keywords: air pollution; hydrogen peroxide; Phaseolus vulgaris

Subjects: cell death, invisible symptoms; cultivar and genotype differences, ozone injury; hydrogen peroxide; ozone injury, early diagnosis, cell death; Phaseolus vulgaris; pollution, air, hydrogen peroxide

Received: March 10, 2004; Accepted: June 8, 2005; Published: December 1, 2005  Show citation