Influence of Ethylene on Morphology and Pigment Changes in Harvested Broccoli

Ethylene and ethylene absorber treatments were used to study the effects of ethylene content on the morphology and pigmentation of broccoli. Results showed that untreated broccoli began to turn yellow 8 days after being harvested at 10 °C. Ethylene treatment caused yellowing to occur 2 days earlier, and ethylene absorber treatment delayed and significantly reduced the degree of yellowing. Yellowing first occurred in the base of the bud; at that time, the shape of the bud had not changed significantly and there was no blooming of the florets. Scanning electron microscopy revealed that the increase in ethylene content caused the calyx cells of broccoli to shrink and that the cell arrangement had become disordered. Ethylene treatment caused increases in the content of chlorophyllide b (Chlide b), pheophorbide b (Pheide b), β-cryptoxanthin, lutein, and β-carotene. The increased degree of yellowing resulted in carotenoids rather than chlorophyll becoming the key pigment (β-cryptoxanthin, β-carotene, and lutein were very significantly correlated with h°). During this change, the expression levels of the BoChl2, BoPaO, BoRCCR, BoPSY, and BoLCYB genes were affected to a greater extent by ethylene. Ethylene absorber treatment did not reduce gene expression, but delayed it. These results indicate that the ethylene absorber only absorbed the ethylene produced and did not directly act on the degradation of chlorophyll. Ethylene also stimulated the expression of BoCCD1 and BoCCD7, resulting in the production of an unknown yellow substance that increased the yellow color of broccoli. In comparison, BoCCD7 expression was more sensitive than BoCCD1.