Structural and physiological changes in the roots of tomato plants over-expressing a basic peroxidase

Previous studies on the tomato (Lycopersicon esculentum Mill.) peroxidase TPX1, including the development of transgenic tomato over-expressing this gene, supported an involvement of this peroxidase in the synthesis of lignin and suberin. The transgenic plants showed a wilty phenotype at flowering, but the relationship between this role in ligno-suberization and this phenotype was not clear. In the present study a histological approach and the measurement of water-related parameters have been performed in order to obtain an insight into the origin of this phenotype. Clear differences between transgenic and non-transgenic roots were observed in the cross-sections of the basal root zones where secondary growth was evident. The diameter of the xylem vessel was diminished in the transgenic plants. Total area corresponding to xylem in the basal cross-sections decreased 3.9 fold in the transgenic roots. In addition, the radial and outer tangential walls of the exodermis cells were more ligno-suberized in transgenic than in non-transgenic plants. After fruit set, predawn and midday water potentials were lower in transgenic than in-non-transgenic plants. At midday, the stomatal conductance was also lower in the transgenic plants, 494±69 versus 594±60 mmol m−2 s−1. Root hydraulic conductances of the transgenic and non-transgenic plants were 1.4±0.38 and 3.47±0.19 g water min−1 MPa−1, respectively. The results obtained support that the phenotype is caused by the anatomical differences found in the transgenic roots. These differences would be the cause of a increased resistance to water flow in the roots that would negatively affect the water supply to the shoot and, as a consequence, resulted in a decreased water potential in the leaves.Estación Experimental La Mayora, CSIC, 29750 Algarrobo-Costa, Málaga, Spain Departamento de Biología Vegetal, Facultad de Ciencias, Universidad de Málaga, Campus de Teatinos S/N, 29071 Málaga, Spain Departamento de Biología Vegetal, Facultad de Ciencias, Universidad de Málaga, Campus de Teatinos S/N, 29071 Málaga, SpainPeer reviewe