Ultrastructural Observations and DNA Degradation Analysis of Pepper Leaves Undergoing a Hypersensitive Reaction to Xanthomonas campestris pv. Vesicatoria |
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| Authors: | Annalisa Polverari Roberto Buonaurio Samantha Guiderdone Mario Pezzotti Mario Marte |
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| Institution: | (1) Dipartimento di Arboricoltura e Protezione delle Piante, Università degli Studi, Borgo XX Giugno 74, 06121 Perugia, Italy;(2) Dipartimento Scientifico e Tecnologico, Università degli Studi, Strada Le Grazie, 37134 Verona, Italy;(3) Dipartimento di Arboricoltura e Protezione delle Piante, Università degli Studi, Borgo XX Giugno 74, 06121 Perugia, Italy |
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| Abstract: | Ultrastructural details of the hypersensitive reaction induced by infiltration with avirulent race 2 Xanthomonas campestris pv. vesicatoria in pepper  Early Calwonder-10R leaves (incompatible interaction) are reported. Affected cells displayed plasmalemma undulations and disruption, lysis of the chloroplast membrane, degeneration of other organelles, general cytoplasm disorganisation and, often, protoplast shrinkage. The nuclei contained large masses of electron-dense material, apparently formed by chromatin aggregation. In many cases a single chromatin-like layer was deposited on the inner side of the nuclear envelope leaving a finely granular matrix in the centre of the nucleus; the nucleolus usually disappeared. The nuclear envelope was sometimes ruptured and the internal matrix leaked into the cytoplasm. The content of many affected cells eventually coagulated and became very electron-dense. The walls often collapsed. All these alterations were especially visible in spongy mesophyll cells at sites where bacteria occurred in the intercellular spaces. Although some of the nuclear and cytoplasmic alterations recall certain aspects of apoptotic cell death, molecular determinations did not reveal any DNA degradation in hypersensitively reacting tissues. The first cell alterations in leaves infected with the virulent bacterial race 1 (compatible interaction) were observed only 27 h after inoculation, when the cytoplasm of some cells showed limited internal disorganisation and plasmolysis at sites where bacterial colonies developed. |
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| Keywords: | apoptosis bacteria chromatin condensation DNA degradation analysis plant programmed cell death |
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