Crystal Formation in Solanum lycopersicum L. Leaves Under Antibiotic Stress Reduced by Non-Thermal Plasma Treated Water

Calcium oxalate (CaOx) crystals in plants can form naturally within their idioblasts but may also be induced by other factors, such as environmental pollution. Here, we report qualitative and semiquantitative results obtained using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) from two experiments in which tomato seedlings were moderately irrigated with Sulfamethoxazole (SMX) and Amoxicillin (AMX) solutions (0.25 mM). Abundant prismatic CaOx co-crystals appeared on the leaf surface induced by these two antibiotics compared to the distilled water (DW) control. Applying a non-thermal plasma (NTP) treatment for 20 min (T20) to the SMX initial solution led to a dramatic suppression of these crystals, with a shift toward spherical structures. Furthermore, the investigation into the composition of both crystal types, indicated different percentual levels of O, C, Ca, K, Mg, S, and Mn as main constituent minerals involved in crystal formation. However, crystal morphology was affected by each applied experimental condition, while detecting their constituent elements depended on their mineral homogeneity at the micro- or macro-field scales. Although both antibiotics induced crystal formation and T20 phenotypically reduced the abundance of the acicular–prismatic crystals by removing the effects of SMX, their mode of action has not yet been clarified.