The effects of mepiquat chloride on the lateral root initiation of cotton seedlings are associated with auxin and auxin-conjugate homeostasis

Abstract

BackgroundMepiquat chloride (MC) is a plant growth regulator widely used in cotton (Gossypium hirsutum L.) production to suppress excessive vegetative growth, increase root growth and avoid yield losses. To increase root growth, cotton seeds were treated with MC to increase the number of lateral root (LRs) and improve drought resistance. An increased indole-3-acetic acid (IAA) pool appeared to correlate with LR growth, and the principal source of IAA in germinating seeds is IAA conjugates. Here, the role of IAA homeostasis and signaling was investigated in cotton seedlings treated with MC.ResultsIn the present research, MC significantly increased endogenous IAA levels in the roots, which promoted lateral root initiation (LRI) by upregulating GhARF7/19 and GhLBD18s and subsequently increasing LR quantity and elongation. The levels of IAA-amide conjugates significantly decreased in MC-treated seedlings compared with untreated control seedlings. Sixteen members of the cotton IAA amidohydrolase (IAH) gene family were identified, of which GhIAR3a, GhIAR3b, GhILR1, GhILL3 and GhILL6 were expressed during cotton seed germination. Compared with those in untreated control seedlings, the expression levels of GhIAR3a, GhIAR3b, GhILR1 and GhILL6 in the MC-treated seedlings were markedly elevated. The GhIAR3a/b and GhILR1 genes were cloned and expressed in Escherichia coli; these recombinant proteins exhibited hydrolytic activity that could cleave IAA-phenyalanine (Phe), IAA-methionine (Met), IAA-glycine (Gly) and IAA-leucine (Leu) in vitro, while only GhIAR3a hydrolyzed IAA-alanine (Ala) efficiently. The content of GhIAR3a, as detected via an established sandwich enzyme-linked immunosorbent assay (ELISA), increased in the MC-treated seedlings compared with the untreated control seedlings. In addition, the Arabidopsis iar3 mutant was less responsive to MC-induced LR growth than was wild type.ConclusionsThese findings suggested that MC application could mediate IAA homeostasis via increased IAA levels from IAA-amide conjugate hydrolysis by accelerating IAH gene expression, which might promote LRI and increase the LR quantity and elongation.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1599-4) contains supplementary material, which is available to authorized users.

Cotton root growth response to mepiquat chloride application in early reproductive stages are cultivar dependent

“…Recent studies have reported that the application of MC via seed treatment stimulates cotton root growth (Chen et al., 2018; Wu et al., 2019) and reduces plant height. Other studies indicate it has no effect on root length (Almeida & Rosolem, 2012).…”

“…The application of MC regulates plant canopy sizes. This makes the plants more compact (Wang et al., 2014) and increases root growth (Chen et al., 2018 and Gao et al., 2019) and carbohydrate concentration in leaves (Tung et al., 2019).…”

High-Performance Liquid Chromatographic Quantification of the Plant Hormone Abscisic Acid at ppb Levels in Plant Samples after a Single Immunoaffinity Column Cleanup

“…The cotton seeds were treated with mepiquat chloride (MC, a plant growth regulator) with soaking seeds with 400 mg/L of MC solution at 30 °C for 12 h . After they were soaked, the seeds were incubated for 3 days in rolls of germination paper (25 cm wide, 38 cm long, catalog number OP1015, Hoffman Manufacturing, Inc., Corvallis, OR) in an incubator at 25 °C and 70% relative humidity.…”

Effect of Plant Distribution Patterns and Growth Regulators on Morphological, Yield and Technological Characters of Egyptian Cotton

“…Moreover, cytokinins are synthetic in root tips and active in the maintenance of ongoing process and nutrients mobilization in the shoots. Chen et al (2018) reported that MC significantly increased endogenous IAA levels in the roots, which promoted lateral root initiation and subsequently increasing lateral root quantity and elongation. Data recorded in the same table showed clearly that, the lower plant height was recorded with foliar application of MC, while kinetin recorded the tallest plants compared to other treatments.…”