Interaction of EPTC and 2,4-D on Excised Tissue Growth

Abstract

Soybean(Glycine max(L.) Merr., ‘Hawkeye 63′) seedling segments from the zone of elongation and corn(Zea maysL., ‘Pioneer 3306) seedling segments were utilized to evaluate the antagonistic interaction ofS-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)-acetic acid (2,4-D). EPTC inhibited growth of the soybean and corn tissue, and 2,4-D in combination with EPTC caused an increase in growth compared to EPTC alone. The 2,4-D-enhanced growth in the presence of EPTC was due to an antagonism of the EPTC inhibition. Inhibition of soybean tissue growth byS-ethyl diisobutylthiocarbamate (butylate) also was antagonized by 2,4-D. Preincubation of soybean tissue in EPTC for 4 hr prior to the addition of 2,4-D did not prevent 2,4-D enhancement of growth. Conversely, the rate of growth was inhibited when EPTC was added after 4 hr of 2,4-D-enhanced growth. The addition of uridine to the incubation media with EPTC did not decrease the EPTC-inhibition of soybean tissue growth. This indicated that EPTC did not inhibit the synthesis of pyrimidine precursors. EPTC vapor losses from the incubation media reduced the inhibitory effect of EPTC to soybean tissue. Also, a growth reduction occurred when the amount of soybean tissue per unit of EPTC was increased.