Effects of hormonal and physical treatments on the expression of a putative chlorophyll b reductase gene (BoNYC1) during postharvest senescence of broccoli

Abstract

Senescence and degreening are the most important features that determine loss of quality during postharvest of broccoli. During senescence, chlorophylls are degraded with the purpose of avoiding presence of photoactive molecules. Chlorophyll b must be previously converted to chlorophyll a in order to be catabolized. This reduction process is catalyzed by two enzymes, chlorophyll b reductase (CBR) and hydroxymethyl chlorophyll a reductase (HCAR). In this work, we characterized the expression of a gene encoding a putative CBR (BoNYC1) during postharvest senescence of broccoli and analysed the effect of several postharvest treatments. BoNYC1 expression increased during first days of postharvest, but decreased in advanced senescence stages, simultaneously with chlorophyll degradation. The effect of different growth regulators and an inhibitor of ethylene action (1-MCP) were analyzed. Treatments with cytokinins and 1-MCP delayed the increment of BoNYC1 expression whereas ethylene accelerated the process. In addition, storage in modified atmosphere, exposure to hot air (45 °C, 3 h), UV-C and white light were also employed. These treatments delayed chlorophyll degradation but only hot air and UV-C delayed the increment of BoNYC1 expression whereas modified atmosphere and visible light caused a higher BoNYC1 expression. In conclusion, most of the hormonal and physical treatments that modify the rate of postharvest senescence of broccoli also affect the expression of BoNYC1.