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Ethylene production from florets of `Shogun' harvested broccoli (Brassica oleracea L.var. italica) 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.

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In Brassica species, hydrolysis of (methylthio)glucosinolates produces sulfur-containing aglycons which have demonstrated anticancer benefits. Selenized Brassicaceae contain (methylseleno)glucosinolates and their selenium-containing aglycons. As a prelude to biological testing, broccoli, cauliflower, and forage rape plants were treated with sodium selenate and their tap roots, stems, leaves, and florets analyzed for selenoglucosinolates and their Se aglycons. Two new selenoglucosinolates were identified: glucoselenoraphanin in broccoli florets and glucoselenonasturtiin in forage rape roots. A new aglycon, selenoberteroin nitrile, was identified in forage rape. The major selenoglucosinolates were glucoselenoerucin in broccoli, glucoselenoiberverin in cauliflower, and glucoselenoerucin and glucoselenoberteroin in forage rape roots. In broccoli florets, the concentrations of selenglucosinolates exceeded those of their sulfur analogues. Fertilization with selenium slightly reduced (methylthio)glucosinolates and aglycons in the roots, but increased them in the florets, the leaves, and sometimes the stems. These discoveries provide a new avenue for investigating how consumption of Brassica vegetables and their organoselenides may promote human health.