Zinc application through seed priming and foliar spray enhanced germination, seedling growth, photosynthetic pigments, and reduced lead toxicity in tomato (Solanum lycopersicum L.)

By interfering with germination, seedling development, physiological processes, and the buildup of toxins in plant tissues, lead (Pb) contamination significantly hinders tomato growth. This study explores the effectiveness of zinc (Zn) seed priming and foliar application in mitigating Pb-induced stress and enhancing physiological performance in tomato plants. A lab experiment was conducted to assess tomato seed germination and seedling growth under Pb stress with Zn priming and foliar application. Pb stress significantly impaired the germination properties of tomato seeds. With improvements in germination percentage, germination index, germination energy, and seed vigor index, Zn application markedly enhanced germination properties. Moreover, Pb stress severely impaired plant growth, water content, photosynthetic pigments, and ionic contents (Ca²⁺, Mg²⁺) while increasing water loss, electrolyte leakage, and Pb content. Foliar application of Zn improved seedling growth, as shown by increases in root fresh weight, root dry weight, shoot fresh weight, shoot dry weight, plant height, root number, and root volume under Pb stress conditions. In addition, relative water content, excised leaf water loss, and electrolyte leakage were improved, while relative water loss was reduced by Zn application. Furthermore, Zn application restored photosynthetic pigment levels under Pb stress. Additionally, Zn application restored Ca²⁺ and Mg²⁺ in leaves, while reducing Pb buildup in roots and leaves under Pb stress. Hierarchical clustering and PCA revealed significant interactions among seedling growth traits, plant water status, pigment levels, and ionic contents under Pb stress and Zn application. Correlation analysis also revealed a strong negative association between lead content and growth or photosynthetic parameters, while water retention and pigment levels were positively correlated. These results demonstrate the great potential of applying Zn to reduce Pb toxicity and enhance tomato plants' physiological and biochemical resilience.