Effect of Oxidase Stresses on Glucosinolates Profile in Broccoli Florets During Postharvest Storage (original) (raw)

Stresses cause production of reactive oxygen species in plant bodies and high levels of stress can be harmful to plant tissues. When sub-acute doses of stresses are applied to postharvest crops, beneficial effects can occur through activation of protection mechanisms. In broccoli (Brassica oleracea), such mechanisms can be induction of glucosinolates and phenolic compounds, which are also beneficial to human health. The objective of this work was to examine sub-acute or hormetic doses as well as extreme doses of UV-B, ozone and hydrogen peroxide on the content of glucosinolates during postharvest storage. Broccoli florets were exposed to hormetic and high doses of UV-B (0, 1.5 and 7.5 kJ m-2); O 3 (5 ppm for 0, 60 and 720 min) and H 2 O 2 (0, 1.25 and 5 mM for 3 h). The profile of glucosinolates and hydroxy-cinnamic acids was determined for up to 14 days in broccoli florets stored at 4°C by LC-MS. The expression of glucosinolate pathway genes (p450 of the CYP79 family-A2, B3 and F1) and phenylpropanoids pathway genes (PAL, CS and F3H1) were also monitored. Titer of neoglucobrassin in UV-B treated broccoli florets at 1.5 kJ m-2 was the highest at the end of the 14 days of storage. However, up regulated expression of genes CYP79B3 and CoL were observed with the high UV-B dose of 7.5 kJ m-2 throughout and at the beginning of the storage, respectively. Both O 3 and H 2 O 2 increased the titers of 4-methoxy-glucobrassicin and 4-hydroxyglucobrassicin; and the florets treated with high ozone dose (5 ppm for 720 min) exhibited an over expression of genes CYP79F1 and CYP79B3, at the beginning of the storage. Results showed a good correlation between gene expression of CYP79B3, and the titers of indole glucosinolates in treated broccoli florets, suggesting that the target of the applied stresses is likely to be the branch pathway of indole glucosinolates.