The application of natural biostimulants is proposed as an interesting approach to ensure sustainable yields and product quality in agricultural and horticultural crops. Here, the effects of foliar application of a protein hydrolysate derived from pig blood (Ppb) on biomass production, phenolic biosynthesis, and the correlation between phenolic profiles and antioxidant activities in lettuce were investigated. The Ppb application significantly enhanced the phenolic content and antioxidant properties in two genotypes of hydroponically cultivated lettuce by increasing the gene expression of enzymes (PAL, CHS, F3H, DFR, F35H, and UFGT) involved in phenolic biosynthesis. However, these changes occurred in a genotype-dependent manner. The results of HPLC and correlation analyses implied that the most contributory phenolic compositions to the increased antioxidant activities in Ppb-treated lettuce were flavonoids and anthocyanins. Meanwhile, no changes were observed in shoot and root fresh weights following Ppb application. These results clearly suggest that Ppb application is a useful strategy to improve antioxidant activities of lettuce by enhancing the biosynthesis of unique phenolic compounds without reducing plant yield.

天然生物刺激素的应用被提议作为一种有趣的方法，以确保农业和园艺作物的可持续产量和产品质量。在这里，研究了叶面喷施源自猪血 (Ppb) 的蛋白质水解物对生菜中生物质产生、酚类生物合成以及酚类成分与抗氧化活性之间的相关性的影响。Ppb 应用通过增加参与酚类生物合成的酶（PAL、CHS、F3H、DFR、F35H 和 UFGT）的基因表达，显着提高了两种基因型水培生菜的酚类含量和抗氧化特性。然而，这些变化是以基因型依赖的方式发生的。HPLC 和相关性分析的结果表明，在 Ppb 处理的生菜中，对增加抗氧化活性贡献最大的酚类成分是黄酮类化合物和花青素。同时，在施用 Ppb 后，地上部和根的鲜重没有观察到变化。这些结果清楚地表明，Ppb 的应用是一种有用的策略，可以通过增强独特酚类化合物的生物合成而不降低植物产量来提高生菜的抗氧化活性。