Effect of Exogenous Ca2+ on Growth and Accumulation of Major Components in Tissue Culture Seedlings of Sophora tonkinensis Gagnep

Background: Sophora tonkinensis Gagnep., well-known for its medicinal properties, grows in karst areas of China characterized by calcium (Ca) and drought. Due to excessive excavation, wild S. tonkinensis is almost extinct. Ca regulates the growth and development of plants and also functions in stress response. Objectives: The effects of exogenous Ca2+ on plant height, stem diameter, enzyme activity, endogenous hormone content, and other traits of S. tonkinensis, and accumulation of matrine and oxymatrine in its active constituents were studied. The purpose was to explore the mechanism of adaptation of S. tonkinensis to high Ca, to protect and artificially cultivate S. tonkinensis resources. Materials and Methods: Six concentrations of Ca2+ (0, 1.495, 2.99, 5.98, 8.97, and 11.96 mmol/L) were used. Agronomic traits were measured with a ruler, vernier calipers, and an electronic scale. Physiological and biochemical indices were measured using ultraviolet spectrophotometry. Endogenous hormone contents were determined by enzyme-linked immunosorbent assay. We determined the composition of oxymatrine and matrine using high performance liquid chromatography. Results: As Ca2+ concentration increased, the drying rate of S. tonkinensis decreased and then increased; root length and number, and rooting rate decreased; and the soluble sugar, soluble protein, and chlorophyll content increased and then decreased. reactive oxygen species increased, increasing enzyme activity to resist cell membrane damage under low concentrations of Ca2+ (0-2.99 mmol/L); high concentrations of Ca2+ (5.98-11.96 mmol/L) did more damage to S. tonkinensis, and enzyme activity was not coordinated. Low concentrations of Ca2+ (0-2.99 mmol/L) promoted methyl jasmonate content to reduce cell damage. Matrine and oxymatrine in the whole plant were highest under 5.98 mmol/L Ca2+ treatment, and in stems, leaves, and roots they were highest under 11.96 mmol/L Ca2+ treatment. Conclusion: S. tonkinensis can tolerate exogenous Ca concentrations between 2.99 and 5.98 mmol/L.