Salinity effects on pigments of Turnera diffusa (Willd.) in vitro

Salinity is an unfavourable factor to plant growth, development, and quality because high salinity increases oxidative stress and damage in plants. Damiana (Turnera diffusa Willd.) plants grow in arid zones. They are socio-economically important as they have industrial potential. Currently, no reports on their tolerance to salinity are available. This study was performed to determine the effect of salinity in damiana plants in an in vitro model under controlled conditions by applying NaCl in three levels (0.1, 1.0, and 1.5%) in Murashige-Skoog medium. To prove decrease in salinity stress, exogenous salicylic acid (SA) treatments (1 and 10 ppm) were tested, and biomass and water content were determined. Photosynthetic pigments and their degradation were determined with high performance liquid chromatography to assess the degree of salinity damage. To define the adaptation mechanism to salinity, specific peroxidase (POX) activity was quantified by spectrophotometric assay. Results showed that the determined parameters (chlorophyll a, chlorophyll b, ß-carotenes, pheophytin, violaxanthin, and zeaxanthin contents) reduced progressively with increase in salinity level. Chlorophyllide a and pheophorbide a contents were not modified by salinity stress but responded to SA presence. POX activity increased in all treatments with plants supplemented with NaCl. Treatments by SA did not modify the negative effects of NaCl on the photosynthetic pigments, but even so significantly enhanced POX activity compared with the untreated stressed plants (NaCl without SA). The results showed that damiana plants were moderately salt-tolerant and could be grown in soils with such characteristics.