Actinomycin D Inhibits the GA3-Induced Elongation of Azuki Bean Epicotyls and the Reorientation of Cortical Microtubules

摘要

Actinomycin D inhibited the elongation of epicotyl segments from azuki bean seedlings that was induced by simultaneous treatment with IAA and GA3. The drug also inhibited the elongation of the segments that was caused by IAA alone when it was applied together with IAA. When the segments were pretreated with GA3and then incubated with IAA, GA3promoted the elongation caused by IAA and brought about a predominance of transverse cortical microtubules (MTs) in the epidermal cells of the segments. The change in the arrangement of MTs caused by pretreatment with GA3was evident 1 h after the start of subsequent incubation with IAA when the effect of pretreatment with GA3on the elongation had not yet become apparent. Pretreatment with GA3did not cause any change in the arrangement of MTs when GA3-pretreated segments were not incubated subsequently with IAA. Although actinomycin D applied before treatment with IAA did not inhibit the IAA-induced elongation, the drug diminished the promotion of the elongation caused by pretreatment with GA3and prevented GA3from bringing about a predominance of transverse MTs when the drug was applied during the pretreatment with GA3.GA3-induced synthesis of mRNA seems to be involved in the promotion by GA3of IAA-induced elongation and in the GA3-induced rearrangement of cortical MTs.