Growth, Nutritional Status, Chlorophyll Content, and Antioxidant Responses of the Apple Rootstock MM 111 Shoots Cultured Under High Boron Concentrations In Vitro

The in vitro response of the apple rootstock MM 111 to increasing concentrations of boron (B) (0.1, 0.5, 1, 3, and 6 mM) in MS medium is reported. The in vitro cultures of MM 111 shoots produced the highest fresh mass when 0.1 mM B was included in the medium. By increasing B concentration of the culture medium from 0.1 to 6 mM, B, phosphorus (P), calcium (Ca), and magnesium (Mg) concentrations of explants increased, whereas potassium (K), iron (Fe), manganese (Mn), and zinc (Zn) concentrations decreased. Chlorophyll content (SPAD units) of leaves declined as B concentration of the culture medium increased from 0.1 to 6 mM. The highest peroxidase (POD) activity in leaves was recorded in the presence of 6 mM B in the medium. By increasing B concentration of the medium from 0.1 to 3 mM, catalase (CAT) activity increased in leaves. Superoxide dismutase (SOD) activity in leaves and stems increased as B concentration of the medium increased. The non-enzymatic antioxidant power activity of leaves (FRAP values) increased gradually as B concentration of the medium increased.