SELENIUM VOLATILIZATION IN ROOTS AND SHOOTS - EFFECTS OF SHOOT REMOVAL AND SULFATE LEVEL

Broccoli plants were grown hydroponically in growth chambers with 20 m u M Se supplied as selenate. The separate contributions of root and sh oot to the volatilization of Se by plants supplied with six different levels of sulfate (ranging from 0 to 10 mM) in half-Hoagland's nutrien t solution were determined. Most of the Se volatilized by broccoli pla nts was from the roots which volatilized about 26 times faster than th e rate of shoots. The removal of the shoot markedly increased the amou nt of Se volatilized over the following 72 h, the detopped root attain ing rates that were 20 to 30 times the rate of the intact root. Compar able results were also obtained for five additional species, rice, cab bage, cauliflower, chinese mustard, and wild brown mustard (Brassica j uncea). Part of the volatilization of Se by plants may involve microbe s, i.e., bacteria. This is indicated by the fact that when prokaryotic antibiotics were added to the nutrient solution, the total rate of Se volatilization by root (broccoli) and nutrient solution was significa ntly decreased, much more than could be accounted for by the loss of m icrobial volatilization from the nutrient solution alone.