Molecular and biochemical characterization of postharvest senescence in broccoli

Postharvest senescence in broccoli (Brassica oleracea L. var Italica) flore ts results in phenotypic changes similar to those seen in developmental. le af senescence. To compare these two processes in more detail, we investigat ed molecular and biochemical changes in broccoli florets stored at two diff erent temperatures after harvest. We found that storage at cooler temperatu res delayed the symptoms of senescence at both the biochemical and gene exp ression levels. Changes in key biochemical components (lipids, protein, and chlorophyll) and in gene expression patterns occurred in the harvested tis sue well before any visible signs of senescence were detected. Using previo usly identified senescence-enhanced genes and also newly isolated, differen tially expressed genes, we found that the majority of these showed a simila r enhancement of expression in postharvest broccoli as in developmental lea f senescence. At the biochemical level, a rapid loss of membrane fatty acid s was detected after harvest, when stored at room temperature. However, the re was no corresponding increase in levels of lipid peroxidation products. This, together with an increased expression of protective antioxidant genes , indicated that, in the initial stages of postharvest senescence, an order ly dismantling of the cellular constituents occurs, using the available lip id as an energy source. Postharvest changes in broccoli florets, therefore, show many similarities to the processes of developmental leaf senescence.