Rapid monitoring of proline accumulation in paprika leaf sap relative to leaf position and water stress

The present study evaluated the pattern of proline accumulation in paprika leaf sap using a modified high-performance liquid chromatography (HPLC) method. Leaf sap samples were extracted using five different solvents and two extraction procedures, and were analyzed using modified HPLC analytical conditions. Enhanced extraction and HPLC analytical conditions were applied to analyze paprika leaf sap obtained from different plant parts (petiole and lamina sap) under different environmental conditions. The results showed that pure water extraction without heating or organic solvent performed best. This newly developed HPLC method was validated and confirmed suitable for analyzing proline content in leaf sap. The proline concentration in both the petiole and lamina sap showed a similar accumulation pattern, exhibiting the lowest proline concentration in the arbitrary node group I (1–5 nodes) and the highest concentration in the VI node group (21–30 nodes). In addition, sap from both the petiole and lamina of side stem leaves showed statistically higher proline content than the main stem leaves. The proline concentration also increased with increasing water stress during both the fruit enlargement and coloring stages, but primarily during the fruit coloring stage. The overall results suggest that the proline concentration in paprika leaves differentially accumulates throughout the plant and can be analyzed by water extraction using a modified HPLC method.