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Cotton Science ›› 2020, Vol. 32 ›› Issue (5): 418-424.doi: 10.11963/1002-7807.lbpdmw.20200817

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Responses and Underlying Mechanisms of Different Mainstem Leaves on Cotton to Defoliant Thidiazuron

Liao Baopeng#, Wang Songman#, Du Mingwei*, Li Fangjun, Tian Xiaoli, Li Zhaohu   

  1. Center of Crop Chemical Regulation, College of Agronomy and Biotechnology, China Agricultural University/ Engineering Research Center of Plant Growth Regulator, Ministry of Education, Beijing 100193, China
  • Received:2019-08-22 Online:2020-09-15 Published:2020-10-09

Abstract: [Objective] This study elucidates the responses of different mainstem leaves on cotton to defoliant thidiazuron and reveal the underlying mechanisms. [Method] Cotton plants were raised hydroponically. At the ten-leaf stage, 4.54 mmol·L-1 thidiazuron was evenly applied to all mainstem leaves, the youngest full-expanded leaf (the fourth leaf from apex) and the youngest leaf (the first leaf from apex). Then, the progress of abscission zone formation and shedding of each leaf was observed, and the expression level of genes related to ethylene synthesis and signal transduction in the fourth and first leaf from apex was analysed. [Result] The abscission zone developed in the following sequence: the first leaf from the top, then the lowest leaves (the ninth or tenth leaf from the top, 35-40 days old), and the fourth leaf from the top. However, the leaf abscission was in a different order: the earliest was the first leaf from apex, then the fourth leaf from apex, and the latest was the lowest leaves which were prone to wither and stick to the stalk. The GhACS1 expression was up regulated in both the first leaf and the fourth leaf from apex within 24 h after thidiazuron treatment. However, the expression of this gene changed more rapidly and sharply in the first leaf from the top than that in the fourth leaf  from the top. In addition, the expression of GhACO1 (ethylene synthesis gene), GhEIN3 and GhERF23 (ethylene signal transduction genes) was significantly increased up to ten times in the first leaf from the top, whereas the expression of these genes did not change in the fourth leaf from the apex. [Conclusion] After exposed to defoliant thidiazuron, the time of the abscission zone formation of different leaves on cotton main stem is different, and the order of shedding is not consistent with that of abscission zone formation. The youngest ready to expand leaf abscises earlier than the youngest fully expanded leaf after thidiazuron treatment, which is possibly associated with the rapid expression change of genes related to ethylene synthesis and signal transduction in the former.

Key words: cotton, thidiazuron, leaf, abscission, ethylene