Effect of Short-Term Treated Wastewater Application on Physiological Traits and Stress-Related Genes (CaCAT2, CaDREB32, CaLOX1) in Pepper

Abstract

This study investigated the effects of treated wastewater irrigation on physiological traits and gene expression in pepper (Capsicum annuum) plants during early development. Control (tap water) and treated wastewater treatments were compared, and physiological parameters, including SPAD values and leaf color measurements, were assessed. In addition, the expression levels of stress-related genes CaCAT2, CaDREB32, and CaLOX1 were analyzed using RT-qPCR. The results showed that treated wastewater irrigation significantly enhanced leaf chlorophyll content and caused a shift in leaf coloration toward darker, greenish tones. At the molecular level, a moderate upregulation of CaCAT2 was detected, whereas CaDREB32 exhibited only a slight and statistically insignificant change. The most pronounced response was observed for CaLOX1, which showed an approximately 50% increase in expression under treated wastewater treatment compared with the control. These findings suggest that treated wastewater irrigation can temporarily enhance photosynthetic capacity in pepper plants, while concurrently activating stress-related signaling pathways. This dual effect highlights that the agricultural use of treated wastewater entails potential benefits but also carries long-term risks that must be carefully considered.