Elevated CO2 Delayed Yellowing by Maintaining Chlorophyll Biosynthesis and Inhibiting Chlorophyll Degradation and Carotenoid Accumulation of Postharvest Broccoli

Yellowing is always accompanied by chlorophyll degradation and carotenoid accumulation, which is an important indicator for evaluating the quality and commercial value of postharvest broccoli. Elevated CO2 treatment was applied in broccoli heads to investigate its effect and mechanism on pigment metabolism. The results demonstrated that 30% CO2 treatment maintained higher nutritional quality by increasing phenols and flavonoids contents and delayed the yellowing by alleviating chlorophyll loss and carotenoid accumulation. The chlorophyll molecule could also be continuously synthesized in postharvest broccoli. The up-regulation of chlorophyll synthesis genes (BoMCase, BoChlM, BoChlE, BoPOR, BoDVR and BoChlG) and chlorophyll combination genes (BoCAB1 and BoCAB2) and the down-regulation of chlorophyll degradation genes (BoSGR1, BoNYC1, BoPPH, BoPAO and BoRCCR) were observed in postharvest broccoli treated with 30% CO2. Additionally, 30% CO2 treatment down-regulated the expression of BoPSY, BoLCYB, BoCHYB and BoVDE, thereby inhibiting zeaxanthin and β-carotene biosynthesis. This study provided new insights into chlorophyll biosynthesis after harvest and the regulation of elevated CO2 on pigment metabolism in postharvest broccoli.