Effect of hydroxytyrosol-rich preparations on phenolic-linked antioxidant activity of seeds

Abstract

Hydroxytyrosol-rich extract (HRE) and hydroxytyrosol-rich olive mill wastewater (HROMW) were used as exogenous growth enhancers to stimulate tomato seedling vigor. The tomato seeds soaking in 10% w/v HROMW or HRE solutions were optimum in maximally enhancing seedling performance according to biochemical seed vigor parameters. Biochemical parameters as the average glucose-6-phosphate dehydrogenase (G6PDH) activity in HRE-treated seeds (915.11 nmoles min−1 mg−1 protein) was higher than control (629.58 nmoles min−1 mg−1 protein) and correlated with the increased phenolic content (3530 μg g−1 fw) and 1,1-diphenyl-2-picrylhydrazyl (DPPH)-based antioxidant activity (70.60%), respectively. Some key enzymes, guaiacol peroxidase (GPX) (6100.65 nmoles min−1 mg−1 protein) and catalase (2.04 μmoles min−1 mg−1 protein), were also higher in response to treatments and correlated with enhanced phenolic content and antioxidant activity. This study supports the hypothesis that the exogenous phenolic application stimulates the pentose phosphate pathway through an over-expression of endogenous phenolic synthesis and an increase in free-radical scavenging antioxidant activity. Therefore, the current study indicates the enhancement of seed vigor by HRE especially and HROMW as reflected by the stimulation of biochemical responses.