A Role for Ethylene in the Yellowing of Broccoli after Harvest

Abstract

<jats:p>Ethylene production from florets of `Shogun' harvested broccoli (<jats:italic>Brassica oleracea</jats:italic> L.var. <jats:italic>italica</jats:italic>) held at 20C in darkness increased as the sepal tissues yellowed. The pattern of respiration rate and ethylene production from branchlets or entire heads was similar, although the magnitude of ethylene and carbon dioxide production appeared to be diluted by the other fleshy stem tissues. The reproductive structures, stamens and pistil, may have a role in determining the rate of sepal degreening, since removing them from florets reduced the yellowing rate. The pistil and stamens also had 7-fold higher levels of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and more than double the ethylene production of other tissues within the floret. Stamen ACC oxidase activity was high on the first day after harvest, before yellowing became obvious. Changes in ACC oxidase activity of the pistil and stamens mirrored changes in ACC content in these tissues. The climacteric status of harvested broccoli was confirmed by exposure to 0.5% propylene. Propylene stimulated respiration and ethylene production and accelerated yellowing (measured as chlorophyll and hue-angle decline). Broccoli tissues did not respond to propylene immediately after harvest. In tissues aged in air before treatment, the time for response to propylene was shorter, a result suggesting a change in tissue sensitivity. Ethylene exposure induced a dose-dependent decline in hue angle, with 1 ppm ethylene giving the maximum response.</jats:p>

Effect of hot air treatments on senescence and quality parameters of harvested broccoli (Brassica oleracea L var Italica) heads

“…8 Moreover, as occurs in many other products, senescence of broccoli florets was clearly related to ethylene production. 2 Heat treatments provoked both diminished ethylene production 13 and an inhibition in the rise of CO 2 production (Fig 2). In senescent tissues, not only sugars are utilised for respiration; in addition, proteins are degraded by proteases and the released amino acids are used as respiratory substrates.…”

“…One of the most visible symptoms of broccoli senescence is the degreening and yellowing of sepals accompanied by chlorophyll breakdown. 2 Lipid degradation is another common feature of many tissues undergoing senescence, and lipid peroxidation is usually correlated with tissue deterioration. 3,4 Protein degradation and turnover are also associated with senescence.…”

Sucrose supply can increase longevity of broccoli (Brassica oleracea) branchlets kept at 22�C

“…The above calculations consider branchlets as a unit, but it appears that stalk tissue may mask some physiological activity of the florets [20]. This effect is evident in Fig.…”

The influence of 6-benzylaminopurine on post-harvest senescence of floral tissues of broccoli (Brassica oleracea var Italica)

“…Chlorophyll loss in broccoli was closely correlated with an increase in endogenous ethylene [8] and, recently, it has been shown that ACC oxidase activity increased in the floral organs of broccoli after harvest [17] . Ethylene production also increased prior to the rapid degreening of the sepals that followed harvest confirming that ethylene may have an important role in the post-harvest senescence of broccoli [17] .…”

“…A rapid decline in respiration may occur very rapidly after harvest [5,7] and other changes may include increased ethylene production [17] and chlorophyll degradation [2] .…”