Aflatoxin B1 influence on excised soya-bean root growth, 14C-leucine uptake and incorporation

The present work reports a portion of our continuing effort to determine the mechanism(s) whereby aflatoxins cause toxic responses in in vitro cultured plant tissues. Few investigations have dealt with the mode of action of aflatoxin B1 (AFB1) in excised plant tissues. Here is detailed AFB1 influence on growth, uptake and incorporation of 14C-leucine by excised, incubated soya-bean roots. Pure AFB1 was added to culture medium prior to autoclaving. One gram fresh weight portions of roots from three-day old soya-bean seedlings were excised and incubated for 4, 8, 12 and 24 hours. Growth was assayed by following changes in root dry weight. Aflatoxin B1 inhibited root dry weight at both 20 and 30 micrograms/ml. Uptake of 14C-leucine was checked by following its depletion from the medium. Reduced 14C-leucine uptake by roots exposed to 20 micrograms/ml AFB1 suggests that the toxin may alter the plasmalemma. A possible role for AFB1 in modification of membrane-associated amino acid transport mechanisms is discussed. Incorporation of 14C-leucine into trichloroacetic acid-precipitable cytoplasm was assayed. Inhibition of this incorporation at 20 micrograms/ml AFB1 was most apparent at 12 hours. Thus, AFB1 may also impair the ability of excised soya-bean roots to carry out protein synthesis.