Some plants produce substances to their own defense against pathogens and predators including fungi, bacteria, viruses, and insects. In lycopersicon species such as tomato, the main antimicrobial compounds is the steroidal glycoalkaloid alpha-tomatine. Tomatine consist of a mixture of two glycoalkaloids: alpha-tomatine and dehydrotomatine. Both compounds are present in all parts of the plant, but the levels of the compounds drastically decrease in the tomato fruit during ripening. The loss of saccharide side chain of tomatine forms the aglycone tomatidine.
In the present study we describe the effects of tomatine and tomatidine as inhibitors of grown of P. serpens, membrane permeability, cell division and induced morphology changes.
Addition of tomatine to the grown medium induced cell death with an IC50 of around 5µM in 5 minutes of incubation, 20µM of tomatine caused death of 90% in less than 5 min. Assays of release of piruvate kinase (citoplasmatic enzyme) shown that 25µM tomatine, concentration that inhibited cell grown, increased the permeability of the plasma membrane. The drug did not abolish the calcium uptake by mitochondria, indicating that it affected preferentially the plasma membrane. Tomatidine (100µM) was unable to release piruvate kinase, in addition assays of mitochondrial calcium uptake also fail, suggesting that the drug did not permeabilize the plasma membrane.
Tomatidine (50µM) added to culture medium arrested the cell grown without apparent death of cells. The number of P. serpens alive continued constant for at least 2 days after the drug. It was found that tomatidine cause a significative reduction of cells in process of division as well as morphological changes with decrease of cellular length, vacuolization, and shortening of flagellum. These changes in morphology were different to the produced by tomatidine on cells resuspended in PBS. In this medium clusters of long and very thin cell were observed.
It is concluded that tomatine kills P. serpens by selective plasma membrane permeabilization, probably by binding to steroids present in the membrane. However tomatidine decrease the ability of cells to divide without apparent effects on the permeability of plasma membrane. Curiously, the morphological changes on the cells were different if tomatidine was assayed on cells in PBS or in culture media suggesting that some additional factor of the medium participates in the mechanism of toxicity.
Supported by CNPq, FAPERJ