| Cotton（Gossypium spp.）is one of the main crops in the world.It is not only an important fiber crop,but also an important oil crop.Gossypol is a kind of secondary metabolite of polyphenol hydroxy binaphthaldehyde,which is unique to cottons,and has the function of preventing pests and diseases.The cotton root is the main synthesis site of gossypol,and it is transported from the root to the above-ground part and stored in the pigment glands.Auxin plays an important role in the formation of root.In this study,cotton seedlings treated with different concentrations of Indole-3-Butytric Acid（IBA）were used as materials to study the effects of IBA on the density of pigment glands,content of gossypol and the key gene expression in gossypol biosynthesis,The main research results obtained are as follows:1 Effect of IBA on cotton plant phenotypeTaking cotton seedlings as the research object,treated with different concentrations of IBA,analyze its number of lateral root growth,stem length and leaf area.It was found that the average lateral root mass of cotton seedlings treated with1×10-6 mol/L,1×10-4 mol/L and 1×10-2 mol/L IBA was 36.51,37.80 and 38.00,respectively,the control was 45.29,which decreased by 19.4%,16.5%and 16.1%after treatment,and the difference reached a significant level.the expression of GhARF6 and GhIAA16 genes related to the auxin signal transduction pathway were significantly increased.The average stem length of cotton seedlings treated with 1×10-4 mol/L and1×10-2 mol/L IBA was 8.7 cm and 7.6 cm,respectively,and that of the control was 4.3cm,which increased by 102.3%and 76.7%after treatment,reach a significant level,GhARF6 gene expression increased significantly under low concentration IBA treatment,and GhIAA16 gene expression increased significantly under high concentration IBA treatment.The average leaf area of cotton seedlings treated with1×10-22 mol/L IBA was 2.69 cm2,and the control was 15.02 cm2,which decreased by82.1%after treatment,at 1×10-10 mol/L,1×10-8 mol/L,and 1×10-6 mol/L IBA treatments were 19.48 cm2,19.45 cm2,and 17.88 cm2,respectively,the increase was29.7%,29.5%and 19.0%after treatment,the difference reached a significant level,and the expression of GhARF6 and GhIAA16 genes increased significantly under low concentration IBA treatment.The above results indicate that within a certain concentration range,the relative content of auxin in roots may increase greatly under the treatment of high concentration of IBA,which inhibits the growth of lateral roots of cotton seedlings,and the relative content of auxin in stems may increase slightly to promote the growth of cotton seedlings,the relative content of leaf auxin may increase slightly under the treatment of low concentration of IBA to promote leaf growth.2 Effect of IBA on density of pigment glandsThe study found that:1×10-4 mol/L IBA treatment cotton seedling in stem density of pigment glands was 2.77 pcs/mm2,the control was 4.12 pcs/mm2,compared with the control,the treatment group decreased by 32.8%,the difference reached a significant level.The density of glands in leaves of cotton seedlings treated with 1×10-8 mol/L IBA was 3.00 pcs/mm2,and the control was 7.26 pcs/mm2,compared with the control,the treatment group decreased by 8.7%,and the difference reached a significant level.It is speculated that external application of IBA can reduce the density of glands by affecting the growth and development of stems and leaves,and has nothing to do with gland differentiation.3 Effect of IBA on content of gossypolThe results of the study showed that 1×10-8 mol/L,1×10-6 mol/L,1×10-4 mol/L and 1×10-2 mol/L IBA were used to treat cotton seedlings,content of gossypol in roots and stems increased significantly,and the expression of key genes GhCDN1,Gh WRKY1 and GhCYP706B1 in gossypol biosynthesis was significantly increased.When cotton seedlings were treated with 1×10-10 mol/L,1×10-88 mol/L,1×10-6 mol/L,and 1×10-4 mol/L IBA,the content of gossypol of leaves was significantly reduced,the GhCDN1 and GhCYP706B1 gene expression level was not significantly different from the control.The above results show that within a certain concentration range,high concentration of IBA can promote the biosynthesis of gossypol in roots and stems,increase the content of gossypol,inhibit the biosynthesis of gossypol in leaves,and reduce the gossypol content.In summary,within a certain concentration range,high concentrations of IBA can inhibit the growth of lateral roots and leaves,promote stem growth,promote the expression of genes related to auxin signal transduction pathway of roots,and the expression of key genes in gossypol biosynthesis of roots and stems,and the content of gossypol. |
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