Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

A NEW TOMATO (LYCOPERSICON ESCULENTUM, MILL.) NECROTIC MUTANT DISPLAYING A KIND OF PLANT CELL DEATH (PCD) TRIGGERED BY HIGH TEMPERATURE AND HIGH LIGHT INTENSITY

FONZO V., MOSCONI P., ZUCHI S., ASTOLFI S., SANTANGELO E.

Agrobiology and Agrochemistry Department, Genetic Section, University of Tuscia, Via S.C. de Lellis s.n.c., 01100 Viterbo

vfonzo@hotmail.com

tomato, necrotic mutant, HR, PCD, callose

Mutants that behave as constantly under pathogen attack, with visible lesions resembling a strong hypersensitive response (HR) have been identified and described in maize, barley, and Arabidopsis. These mutants can occur naturally, following artificial mutagenesis and by constitutive transgene expression and the necrosis appearance can be triggered by developmental stage, hormone level, temperature and light regime, chemical agents (Marchetti et al., 1983; Dietrich et al., 1994; Greenberg et al., 1994; Abad et al., 1997; Chamnongpol et al., 1998).

A new necrotic mutant recently (Soressi, 1999, personal communication) recognized in tomato (Lycopersicon esculentum, Mill.) displays necrotic lesions in older leaves in presence of high temperature and light intensity threshold . At the beginning, the lesions appear as pale yellow spots that afterwards enlarge, coalesce and brown, spreading on the whole lamina. This phenotype, mimicking that of PCD, shows an acropetal trend in the plant, starting from the basal oldest leaves towards the youngest upper ones. Therefore, when the process has been activated, three parts are clearly distinguishable on the whole plant: a basal necrotic portion; a median zone with green leaves showing pale-chlorotic halos; and an apical part where the leaves are entirely green. At single leaf level, the lesions start from the distal oldest leaflet towards the youngest proximal one. Through grafting experiments, we have proved that the signal inducing the necrotic reaction has not a systemic way of spreading, but presumably is triggered locally depending on particular environmental conditions (temperature, light) and leaf age.

Taking into account the progression of the necrosis, leaf samples from the three above mentioned plant zones show a significant difference for physiological parameters common to plant defense mechanisms. The callose production was detectable only in the basal necrotic leaves but not in the apical green ones. Moreover, differences have been observed for the activity of peroxidase, catalase and H⁺ATPase enzymes, known to be involved in the primary plant defence response. Crosses are in progress in order to verify the genetic basis of the mutant phenotype.

Taking into account the interest of studying mutants altered in the control of PCD, this new necrotic mutant available in a model species like tomato is a suitable tool for shedding new light on the mechanisms used by the plant to respond to environmental stimuli.