Enhancing Cucumber Tolerance to Zinc Stress Through Grafting: A Comprehensive Study on Biochemical, Hormonal, and Metabolic Responses

Abstract

Background: Zinc (Zn) is an essential micronutrient for plant growth and development, yet excessive or deficient Zn levels can disrupt physiological processes and reduce yield by impairing photosynthesis, nutrient uptake, and antioxidant balance. Grafting has been proposed as a promising strategy to enhance plant resilience against abiotic stresses, including heavy metal toxicity, by improving root system efficiency, regulating hormone signaling, and enhancing antioxidant defense. This study aimed to investigate the effects of grafting and different rootstocks on mineral uptake, biochemical responses, and metabolic adjustments in cucumber (Cucumis sativus L.) plants exposed to zinc stress under controlled greenhouse conditions. Results: Under zinc-deficient conditions, manganese (Mn) content increased to 26.3 mg/kg in plants grafted onto the TZ148 rootstock, which was approximately 135% higher than in non-grafted plants (11.2 mg/kg). At 10 ppm Zn, catalase (CAT) activity reached 300 units in TZ148-grafted plants (22% higher), while superoxide dismutase (SOD) activity peaked at 760 units in Maximus-grafted plants (53% higher), relative to non-grafted controls. Proline content peaked under 50 ppm Zn, especially in TZ148-Çağla and non-grafted plants, indicating a strong osmotic adjustment response. At 50 ppm Zn, vitamin C content reached 0.12 units in TZ148-grafted plants (50% higher than non-grafted plants). Under zinc deficiency, gallic acid content in the Maximus-Çağla combination increased from 1.8 to 2.4 units, corresponding to a 33% increase compared to the control. Correlation analysis revealed strong positive associations, such as between gallic acid and quercetin (r = 0.91) and between delphinidin-3-glucoside and petunidin-3-glucoside (r = 0.98), indicating coordinated regulation of related metabolic pathways. Conclusions: The results demonstrate that grafting, especially using the TZ148 rootstock, enhances cucumber tolerance to zinc stress by improving mineral uptake, boosting antioxidant enzyme activities, and promoting the accumulation of stress-related metabolites such as proline, phenolics, and anthocyanins. Rootstock selection, especially TZ148 and Maximus, represents an effective strategy for improving cucumber productivity and quality in Zn-stressed environments, contributing to sustainable agricultural practices.