Effects and Absorption of Sethoxydim on Excised Root Tips of Corn ( Zea mays) and Pea (Pisum sativum)

Abstract

The mechanism of selective herbicidal action of sethoxydim was investigated by using cultured root tips of corn and pea. Sethoxydim inhibited the growth of susceptible corn root at concentrations of 3 nᴍ and above, but did not affect that of pea at 0.1 mᴍ. Meristematic cells in cultured roots were arrested at the G1 and G2 stages of the cell division cycle by sucrose starvation, and resumed growth and cell division (proliferation) upon sucrose addition. Corn root growth was not inhibited by sethoxydim even at 0.01 mᴍ when the roots were arrested by sucrose starvation. Corn roots that resumed growth upon sucrose provision were more sensitive to sethoxydim than those kept in constant growth condition. Better absorption of [14C]sethoxydim into the meristematic region of corn roots was observed when cells were in the proliferative condition, which was not observed when cells were arrested by sucrose starvation. No stronger uptake of the herbicide was observed into pea meristems in either growth condition. In the cell cycle study, stronger absorption of [14C]sethoxydim into the corn root meristem took place at a certain limited period prior to the S (DNA synthesis) stage. The physiological effects and the better absorption of sethoxydim clearly depended on cell cycle progression of the corn root meristem, while fatty acid synthesis, as well as its inhibition by sethoxydim, was neither associated with cell cycle progression nor with stronger absorption of the herbicide. The selective herbicidal action of sethoxydim may be caused by interference with selected stages (G1 and/or the transition step between G1 and S stages) of the cell division cycle, where affinity sites for the herbicide might be expressed.