Controlled atmosphere treatment of broccoli after harvest delays senescence and induces the expression of novel BoCAR genes

The current study examines the transcription of four genes (BoCAR1A, BoCAR5, BoCAR6-4 and BoCAR25) found to be up-regulated in response to high CO2/low O2 treatment in broccoli (Brassica oleracea). Messenger RNA levels for the four genes declined after tissues were removed from CA. Physiological and biochemical changes and gene expression patterns were examined in broccoli tissues held in one of four different atmospheres, namely air (<1% CO2, 21% O2), high carbon dioxide and low oxygen (CA 10% CO2, 5% O2), low oxygen (0% CO2, 5% O2), and high carbon dioxide (10% CO2, 20% O2). In a second trial gene expression was examined in tissues held for short periods in CA (6 h, 12 h or 24 h) followed by air. Broccoli tissues were also exposed to CA after 48 h in air to determine whether CA treatment was effective in up-regulating the CA-responsive genes and/or delaying senescence after early senescence-associated gene changes had been initiated. Northern analysis showed that a combined high CO2 and low O2 atmosphere was more effective than high CO2 or low O2 alone for inducing maximum gene expression and delaying postharvest broccoli senescence. In addition, broccoli tissues responded to CA treatment after a 48-h period in air with increased CA-responsive gene expression. Certain transcripts were down-regulated in tissues exposed to salt and water stresses that promoted senescence, and down-regulated in tissues treated with cytokinin, a treatment that delays postharvest senescence in broccoli. The up-regulation of these four BoCAR genes appears to be specific to CA treatment in harvested broccoli tissues.