Time of day at harvest affects the expression of chlorophyll degrading genes during postharvest storage of broccoli

Abstract

Broccoli is an important component of the human diet with a high nutritional value. This vegetable is harvested when its development is not complete, triggering a quick senescence that is accompanied by chlorophyll degradation and a shortening of shelf life. Recently it was shown that the time of the day at which the broccoli is harvested can influence in the rate of chlorophyll degradation. This report describes changes of expression of chlorophyll degrading related genes during postharvest storage of heads harvested at different moments of day. At harvest, the content of chlorophyll did not change among samples but the expression of many genes associated with chlorophyll degradation did. The level of chlorophyll diminished during storage, but samples harvested at 18:00 h had a lower rate of degradation in comparison with heads harvested at 08:00 h. Most of genes that were previously associated with chlorophyll degradation during senescence such as BoSGR, BoCLH2, BoPPH and BoPaO showed a lower expression or a delay in their mRNA level increments in samples harvested at 18:00 h. Other genes related to chlorophyll degradation during senescence, like BoNYC or BoRCCR, showed an increased expression during senescence but there was no positive correlation between chlorophyll catabolism and expression of these genes. In conclusion, changes in the metabolism due to time of day at harvest not only influence the expression of genes during the day but also may cause different patterns of expression during postharvest.