Characterizing the effects of salt stress in Calendula officinalis L

In this study the effects of salt stress on growth and several stress markers were investigated in the ornamental and medicinal plant Calendula officinalis. One-month-old plants were submitted to increasing salt concentrations, up to 150 mM NaCl, for a period of 30 days. Salinity affected growth in terms of relative reduction of stem length and fresh weight of the plants, but water content remained unchanged indicating a certain tolerance to low and mild NaCl concentrations. Although Na+ and Cl- increased in parallel to increasing salinity, the levels of K+ and Ca2+ showed no significant change, while Mg2+ levels recorded a twofold increase upon the application of the highest salt concentration. Other measured parameters showed a more significant change, notably proline levels, which registered a nine-fold increase in the presence of 150 mM NaCl. In conclusion, although plants suffered from salt stress, as shown by the degradation of photosynthetic pigments and induction of oxidative stress (increased MDA levels), they continued their vegetative growth under low concentrations of salt. The main mechanisms of response to salt stress in this species appear to be based on the maintenance of K+ and Ca2+ homeostasis and the accumulation of proline as a functional osmolyte.