Silvia Milrad de Forchetti

Peroxidase activity and isoenzymes in the culture medium of NaCl adapted tomato suspension cells

The medium of tomato (Lycopersicon esculentum) cells adapted to grow in the presence of 15 g l−1 NaCl had a higher peroxidase activity than the medium of an unadapted tomato cell line. When the adapted cells were cultured in a medium without NaCl, the value found for peroxidase activity was intermediate. The increase in peroxidase activity was parallel to an increase of lignin-like compounds in the cell walls, as well as to an increased content or appearance of neutral and basic peroxidase isoenzymes. Apparently, the high values of peroxidase activity in the medium of the salt-adapted cells reflect the changed mechanical properties of the cell wall which, in turn, could be related to the salt adaptation process.

Production of peroxidases by hairy roots ofBrassica napus

Hairy roots cultures derived from leaf explants ofBrassica napus L. produced and secreted peroxidases. The enzyme activity in the medium increased with growth but it remained nearly constant in the tissue. The changes in extracellular peroxidase activity seemed to be correlated with the increase in a basic peroxidase of pI: 9.6. Four isoenzymes with pI in the range 8.5–9.6 and a neutral peroxidase of pI 6.3 were the most important peroxidases detected in cell extracts. Ca2+ addition at the beginning of the culture stimulated both the excretion of peroxidase to the medium and the enzyme activity in hairy roots but the isoenzyme profiles did not show qualitative changes during the growth cycle for both culture conditions.

Tomato root peroxidase isoenzymes: kinetic studies of the coniferyl alcohol peroxidase activity, immunological properties and role in response to salt stress

Summary More than eleven soluble and ionically-bound cell wall peroxidase (EC 1.11.1.7; donor: hydrogen-peroxidase oxido-reductase) isoenzymes were found in tomato ( Lycopersicon esculentum (L.) Mill. cv. Pera) roots. Isoperoxidases with isoelectric points 9.6, 8.2, 7.5, 6.5, and 3.6, were partially purified by ammonium sulfate precipitation, gel filtration on Sephacryl-S200 and ion exchange chromatography on DEAE Sephacel and/or SP-Sephadex C50 columns. Isoenzymes of pI 9.6, 3.6, and 6.5 showed the highest catalytic efficiencies with coniferyl alcohol, a true monolignol, used as substrate marker of peroxidases presumably involved in lignification. In addition, they showed cross-reactivity in Western blots of crude extracts when antibodies anti pI 3.6 isoenzyme were used for the immunodetection, despite their different pI values. It was demonstrated that the levels of pI 3.6 isoenzyme increased with the time of growth but did not respond to salt stress, unlike the isoenzyme with pI 9.6, which did. Thus, the expression of peroxidase isoenzymes involved in lignification may be differentially controlled by either developemental or stress signals.

Tomato (Lycopersicon esculentum cv. pera) hairy root cultures: Characterization and changes in peroxidase activity under NaCl treatment

SummaryHairy root cultures of Lycopersicon esculentum L. Mill ev. Pera were established by infection of leaf explants with Agrobacterium rhizogenes LBA 9402. The pattern of peroxidase isoenzymes in these tissues was similar to that of roots excised from tomato plants grown in hydroponic cultures. Hairy root cultures may be an appropriate system to analyze the peroxidase involvement in the response of isolated roots to salt stress, avoiding the problem of wounding or changes in hormone levels observed in roots excised from plants. The cultures of hairy roots allowed the evaluation of changes in peroxidase patterns not only in the tissue but also in the culture medium. Hairy roots were subcultured in Murashige and Skoog liquid medium with or without 100 mM NaCl to investigate the evolution of growth, total peroxidase activity of the tissue and culture medium, and changes in the peroxidase isoenzyme patterns under each condition of growth. Control cultures showed a growth index higher than those reported for other hairy root cultures, and it was even higher in the presence of 100 mM NaCl. The total peroxidase activity in the tissue was similar for control and salt-treated roots. Even when the total peroxidase activity of the medium decreased under salt treatment, NaCl induced secretion of a highly basic peroxidase and inhibition of the secretion of some acidic isoenzymes. These changes may explain the physiological role of these enzymes in the response to salt stress that we will possibly establish through a future study of the biochemical properties of those peroxidases.