RNA Synthesis as the Basis for EPTC and 2,4-D Antagonism

Abstract

Three-day-old soybean(Glycine max(L.) Merr., ‘Hawkeye 63′) hypocotyl segments (0.5 to 1.5 cm below the cotyledons) were utilized to evaluate the effects of the antagonistic interaction ofS-ethyl dipropylthiocarbamate (EPTC) and (2,4-dichlorophenoxy)acetic acid (2,4-D) on growth and nucleic acid synthesis. EPTC inhibited growth and RNA synthesis in soybean tissue. The addition of 2,4-D with EPTC was antagonistic to EPTC inhibition of growth and caused an increase in total RNA synthesis. Analysis of soybean tissue nucleic acids by methylated-albumin-kieselguhr(MAK) column chromatography showed that EPTC inhibited ribosomal-RNA (r-RNA), DNA like RNA (D-RNA), and tenaciously-bound-RNA (TB-RNA) synthesis. The combination of 2,4-D with EPTC caused an increase in D-RNA and TB-RNA synthesis compared to the EPTC treatment alone. The 2,4-D-enhanced synthesis of D-RNA and TB-RNA in the presence of EPTC appears to be the basis of the antagonism between EPTC and 2,4-D. Preliminary analysis of r-RNA indicated that EPTC preferentially inhibited the synthesis of 18S r-RNA more than 25S r-RNA and that 2,4-D had no effect on this selective inhibition.