Aflatoxin - induced alteration in the levels of membrane chemical of subcellular organelles isolated from excised, incubated glycine max, cv. "Essex" roots. I. Non-enriched organelles.

Abstract

Isolates of aflatoxin-producing strains of Aspergillus grow on autoclaved and field-grown (lesser extent) Glycine max beans. Both mixed and aflatoxin B1 inhibit G. max, cv. ‘Essex’ bean germination and elongation of either attached or excised cultured roots. Because B1 impairs the latter roots' ability to intracellularize [14C]-leucine, it may alter plasmalemma structure and/or function. To determine whether incubation of excised roots for 18 hours in toxin-containing medium could affect cellular membrane chemical content, organelles were isolated by differential centrifugation (1 000, 40 000, and 80 000 xg) of homogenates and characterized chemically. Statistically significant differences between treated and untreated roots in acid insoluble protein but not either sterol or lipid phosphorus levels were observed for both 40,000 and 80,000 xg pellets. Protein and sterol recoveries were 81 (treated) and 84 (untreated) % for the former and 77 (treated) and 79 (untreated) % for the latter. Lipid phosphorus recoveries were 87.3 (treated) and 136 (untreated) % with and 96 (treated) and 83 (untreated) without membrane stabilization. Protein:sterol:lipid phosphorus were 35.7∶4.5∶1 (1 000 xg), 18.9∶3.6∶1 (40000 xg), 26.3∶4.6∶1 (80 000 xg) and 1,010∶29∶1 (80 000 xg supernatant) for untreated and 36.9∶3.3∶1 (1,000 xg), 23.1∶3.8∶1 (40 000 xg), 36.2∶4.8∶1 (80 000 xg) and 1,053∶21.7∶1 (80 000 xg supernatant) for treated roots. Significant differences in RNA content between treated and untreated roots were found for both 1 000 and 40 000 xg pellets but not for the 80 000 xg pellet and its supernatant. Whereas a significant increase in the 1 000 xg pellet occurred upon treatment, a decrease was noted for the 40 000 xg pellet but not for the 80 000 xg pellet and its supernatant. Similar pH 6 (plasmalemma marker enzyme) and 9 (mitochondrial marker enzyme) K+-stimulated ATPase activities were demonstrated for 40 000 and 80 000 xg pellets. The 1 000 xg pellet contained greater than 50% of the NADH-cytochrome c-reductase activity (endoplasmic reticulum marker enzyme) recovered from fractions examined for this activity which was absent from the 40 000 xg pellet. Both the 80 000 xg pellet and its supernatant possessed equivalent reductase activities. Inosine diphosphatase activity (dictyosome marker enzyme) was not present in 1 000 xg pellets obtained from either treated or untreated roots but was in both 40 000 and 80 000 xg pellets. Based on these results, a tentative assignment of organelles to each fraction (xg force) is reported.