IAA priming improves the germination and seedling growth in cotton (Gossypium hirsutum L.) via regulating the endogenous phytohormones and enhancing the sucrose metabolism

Seed priming is an effective technology of promoting seed germination and plant growth in crop production. This study investigated IAA as a seed priming agent in cotton, because auxins regulate plant growth and development, as early as seed germination and seedling growth. Exogenous IAA (20 mg L−1) was applied to initiate the cotton seeds, and the phenotypic and relative biological changes of germinating and germinated seedling were examined. After IAA priming, the seed germination ability was significantly promoted based on germination rate, index and speed. In seedlings at the end of germination test, the content of endogenous phytohormones were in pattern to favor the growth of germinating seedlings, and sugars contents including sucrose, glucose and fructose were also increased, as a result of the enhanced activities of enzymes related to sucrose metabolism. It was indicated that IAA priming could accelerate the seed germination by regulating the endogenous hormones and sucrose metabolism. Moreover, during seedling stage, seedlings from seeds with IAA priming showed more vigor growth with improved root length, seedling height, biomass and leaf photosynthesis capacity. That was also accompanied with increased sugars contents and the activities of key enzymes in sucrose metabolism as well as a better counteractive balance of key endogenous phytohormones in the seedlings. Therefore, IAA priming resulted in enhanced seed germination and seedling growth, along with favorable shifts in endogenous phytohormones and sucrose metabolism, suggesting that it has favorable regulatory effects on these growth parameters. The simple application of IAA to improve cotton seedling establishment in this study showed its potential for application of this technology on increasing cotton crop production.