Subcellular Distribution of Aluminum, Bismuth, Cadmium, Chromium, Copper, Iron, Manganese, Nickel, and Lead in Cultivated Mushrooms (Agaricus bisporus and Pleurotus ostreatus)

Abstract

In this work, the distribution of nine metals in two types of cultivated mushroom had been investigated. For Agaricus bisporus, the biomass was separated into caps and stalks, and for Pleurotus ostreatus, the entire mushrooms were taken for analysis. Electrothermal atomic absorption spectrometry was used for total element determination in acid digests. For accuracy checking, the certified reference material (NIST 1,571, citrus leaves) was analyzed. The results obtained for the two fungi species were within the ranges of concentration reported previously by other authors. Subcellular fractionation was accomplished by centrifugation of cell homogenates, which had been suspended in Tris-HCl buffer. In the first centrifugation (7,300 g, 4 degrees C, 10 min), cell walls were separated (pellet I), and the second centrifugation (147,000g, 4 degrees C, 60 min) yielded mixed membrane fraction (pellet II) and cytosol (supernatant II). Recoveries of the fractionation procedure were in the range 70--100% (with the exception of Fe). For all elements studied, the highest relative contributions were found in cytosol fractions of the fruiting bodies (63--72%, 49--76%, 44--93%, 26--87 pc, 55--85%, 50--68%, 41--78%, 39--78%, 54--67% respectively for Al, Bi, Cd, Cr, Cu, Fe, Mn, Ni, and Pb. Lower contributions were found in cell walls (respectively 22--32%, 24--44%, 6.1--47%, 12--52%, 7.3-- 37%, 7.9--32%, 19--52%, 20--42%, and 25--38%) and only minute amounts in the mixed membrane fraction (3.0--5.8%, 0.7--7.0%, 0.7--8.3%, 1.0--22%, 7.5--14%, 16--24%, 1.1--19%, and 5.1--7.7%). The results obtained indicate that small water-soluble molecules were the primary forms of nine elements in two mushroom species studied. On the other hand, the evidence has been provided on elements binding to larger, water-insoluble molecules contained in the structures of cell wall and membranes. The relative distribution was both element and fungi dependent. Thus, in P. ostreatus, total element levels were higher than in A. bisporus, with the preference for their accumulation in cytosol. On the contrary, total element content in the latter fungi was lower; however, a clear tendency toward more efficient element incorporation to the water-insoluble structures was observed (no apparent differences between stalks and caps).