Mechanism of cyclanilide enhanced the defoliation efficiency of thidiazuron in cotton by regulating endogenous hormones under low temperature stress.

The technology of cotton leaf removal is an important prerequisite for realizing the mechanical harvesting of cotton, but low temperature affect the efficiency of TDZ-induced leaf abscission, which cannot meet the requirements of mechanized harvesting. In our laboratory, we found that cyclanilide (CYC) could improve the defoliation efficiency of TDZ at low temperature, but the mechanism of CYC promoting chemical defoliation (TDZ) under low temperature is unknown. Therefore, the content of plant hormones and the relative expression level of related genes in the abscission zone of cotton leaves were analyzed using Zhongmian 425 as the experimental material, setting two temperature levels (25 and 15 ) and three treatments [water (CK), single TDZ (T), and the compound of TDZ+CYC (TC)]. At 240 h after treatment under low temperature (15 ), the abscission rate of cotton leaves treated by T was only 53.0%, while the start time of cotton leaves abscission treated by TC was 24 h ahead of that treated by T and the abscission rate of cotton leaves treated by TC increased to 79.6%. At low temperature, compared with T, the relative expression level of auxin (IAA) transport genes (LAX2, PIN1), IAA response genes (IAA9, ARF3) and the content of IAA in the abscission zone of cotton leaves treated with TC were reduced significantly; the relative expression level of ethylene (ET) synthesis genes (ACS, ACO), and the content of ET synthesis precursor ACC were increased, the relative expression level of ET downstream signal gene(ERF1B) was up-regulated significantly in the abscission zone treated with TC. The jasmonate acid (JA) synthesis-related gene (AOC4) was up-regulated, and the content of JA was increased in abscission zone treated by TC. The inhibition of the IAA transport and signal transduction and the promotion of ET and JA synthesis and ET signal transduction caused by TC treatment in the abscission zones of cotton leaves could be the key reason that CYC could promote cotton leaves abscission effect of TDZ at low temperature. [ABSTRACT FROM AUTHOR]