Abstract:【Objective】The accumulation of lignin is the main process of walnut endocarp development, and plant hormones in the formation of thick-walled tissues and the synthesis of lignin can be involved in xylem development through the expression of genes related to the regulation, thus affecting the development of the secondary wall, in order to understand the effect of the growth hormone IAA on the development of endocarp in walnuts.【Methods】In the present study, we selected the trees of age of 16, with robust and consistent growth and consistent levels of water and fertilizer management level consistent trees. At about 50 d after flowering, walnut short fruiting branches were wrapped and treated with different concentrations of growth factors. Changes in lignin deposition in the endocarp of walnuts after treatment with different concentrations of IAA were observed by resorcinol staining, and the contents of lignin, cellulose, hemicellulose, IAA in the endocarp were determined, and at the same time, samples from the 12th d of IAA treatment were subjected to high-throughput sequencing and analyzed.【Results】The results showed that at the early stage of treatment, there was a significant difference in the accumulation of endocarp lignin between the low concentration IAA treatment and the high concentration IAA treatment, with the deposition starting first from near the vascular bundles, and the color shifting from light red to dark red, and from local staining to overall staining; at the late stage of treatment, the endocarp of the late walnuts was partially hardened and significantly thickened, but the development of the endocarp was incomplete, and the dewy kernel was still present. By determining the lignin, cellulose and hemicellulose contents, it was found that the endocarp lignin content increased significantly after treatment with 50 mg·L -1 IAA and 100 mg·L -1 IAA on the 12th d after treatment, and that the difference between the lignin content and the control was not obvious after 200 mg·L -1 IAA treatment. In the late treatment period, low concentration IAA treatment promoted lignin accumulation and lignin content increased slowly, and endocarp lignin content was lower than control after high concentration IAA treatment. The overall endocarp cellulose content showed an increasing trend, compared with CK, the pre-cellulose content was higher than the control after different concentrations of IAA treatment; compared with CK, the overall endocarp hemicellulose content showed an increasing trend. The endogenous IAA content of walnut endocarp after different concentrations of IAA treatments showed an overall increasing trend. On the 12th d after treatment, the endogenous IAA content of walnut endocarp after 50 mg·L -1 IAA and 100 mg·L -1 IAA treatments was significantly higher than that of the control, and the IAA content of the endocarp after 50 mg·L -1 IAA treatments amounted to 37.77 ng·g -1 , which was 24.2% higher than that of the control, and that of the endocarp after 100 mg·L -1 IAA treatment was 21.5% higher than the control, 150 mg·L -1 IAA and 200 mg·L -1 IAA were lower than the control, and with the increase of concentration, the IAA content showed a decreasing trend. The different concentrations of growth hormone IAA and water (control CK) were compared to each other to screen for differential genes, and it was found that the number of differentially expressed genes after 50 mg·L -1 IAA vs CK treatment was the largest, with 3,292 genes, of which 1,922 were up-regulated genes and 1,370 were down-regulatedgenes, and the common differential genes among the different concentrations were 591 genes through the Veen diagram. expressed genes were 591. The GO enrichment and KEGG enrichment analyses revealed that the phytohormone signaling pathway was the common metabolic pathway, and the phenylpropane biosynthesis pathway was significantly altered with the increase of concentration, and it was not enriched in the treatments of 150 mg·L -1 IAA and 200 mg·L -1 IAA; it was initially hypothesized that there were significant differences in the phytohormone signaling and phenylpropane biosynthesis metabolic pathways in the endocarp of walnuts after exogenous application of growth factors, so the above two pathways were investigated and analyzed. Therefore, statistical analysis of the genes related to the above two pathways showed that some of the differentially expressed genes related to hormone signaling and phenylpropane biosynthesis were gradually down-regulated or non-expressed with the increase of concentration.【Conclusion】 The results showed that IAA affected the accumulation of lignin and lignin content of endocarp, as well as the expression of differentially expressed genes in the lignin synthesis pathway, which provided a reference basis for the later study of the mechanism of exogenous growth hormone's effect on walnut endocarp.
PDF （）