Exogenous quercetin as a proliferation stimulator in tobacco BY-2 cells

Quercetin (Q) is a prominent flavonoid with a remarkable spectrum of biochemical activities. Its impact on human health as well as its endogenous role in the development of plants have been studied extensively. However, the impact of exogenous quercetin on plant cells is still uncharted. In this study, the influence of exogenous quercetin on Nicotiana tabacum, L. cv Bright Yellow 2 cell growth, viability, morphology and DNA content was investigated. The cells were exposed to quercetin at different concentrations (0.001, 0.01, 0.1 and 1 mM) during two phases of cell growth: from the start of a new culture (day 0), that is during the lag phase, when the cells are transferred to a new medium and they adapt to new growth conditions (model A), and on the fourth day after passaging (day 4) during the logarithmic phase of growth (the log phase), when the number of new cells appearing per unit time is proportional to the present population (model B). This is a period of intensive proliferation. The BY-2 cultures were maintained for 8 days. The proliferation level of BY-2 cells as well as their viability were analyzed every day during the experiment. The results showed that quercetin in a dose below 0.1 mM stimulated cell proliferation and viability, thus it could be a promising biostimulator. On the other hand, the highest concentration (1mM) arrested the cell cycle in G2 phase and led to cell death. Application of 1 mM Q during the lag phase dramatically increased cell mortality and at the end of the experiment all BY-2 cells were dead, whereas an application during the log phase had a significantly milder effect; under the same concentration only 34% of cells were dead at the end of the stationary phase of growth. Thus, the results suggest that Q was less toxic even in very high concentrations when it was added to cells in the log phase of growth. This is probably related to the transfer of cells to a fresh medium, which causes great stress and supplementation with a high concentration of Q seems to aggravate this stress.