Effects of phosphorus application on carbohydrate metabolism in cottonseed kernel during the key development period provided a new insight for phosphorus management in cotton production

Abstract

Cottonseed provides abundant and high-quality raw materials for biodiesel, fine chemical, and other industries due to its rich oil, but phosphorus-deficient farmland and finite phosphate resource hinder its production. Cottonseed development is based on its carbohydrate, and exploring the response of cottonseed carbohydrate metabolism to phosphorus could contribute to optimizing phosphorus management in cotton production and continuously obtaining high-quality cottonseed. Here, the experiment on phosphorus rates [0 (phosphorus deficient), 100 (phosphorus critical), and 200 (phosphorus excess) kg P2O5 ha−1] was conducted using Lu 54 (low-phosphorus sensitive) and Yuzaomian 9110 (low-phosphorus tolerant) in a field containing 16.9 mg kg−1 available phosphorus to assess the effects of phosphorus on cottonseed yield, cottonseed total phosphorus, ash, and oil contents, carbohydrate metabolism related carbohydrate contents, and enzymes activities. The results showed that phosphorus application increased cottonseed yield and oil content by 32.4%−54.2% and 14.8%−20.1% on average, respectively, which could be attributed to the improvements in sucrose transport and hydrolysis in cottonseed kernel during 18–26 days post anthesis induced by higher total phosphorus content (17.1%−26.7%). During the key development period of cottonseed kernel, phosphorus application increased sucrose content (13.0%−19.4%) by increasing the expression of sucrose transporter genes, and promoted sucrose hydrolysis by elevating enzymes activities, especially sucrose synthase (11.2%−19.1%) in cottonseed kernel. Consequently, phosphorus application increased hexose levels in cottonseed kernel and thus provided more substrates for its development, which promoted the formation of cottonseed kernel biomass (6.2%−10.6%), cottonseed and oil yields. Additionally, carbohydrate metabolism in Lu 54 was more sensitive to phosphorus than Yuzaomian 9110 during the key development period, resulting in greater increases in cottonseed kernel biomass, cottonseed yield, and oil content for Lu 54. Notably, the increments generated by unit phosphate fertilizer on the above indicators attenuated markedly with phosphorus application. Based on sucrose content, the key substance, the critical phosphorus concentration in the subtending leaf to cotton boll (LPC) needed by the efficient operation of the key carbohydrate metabolic pathway was 0.38% for Lu 54 versus 0.34% for Yuzaomian 9110. This report first unveiled the key carbohydrate metabolic pathway regulated by phosphorus for cottonseed and oil yield formation and its demand for LPC during the key development period, providing a new insight for diagnosing and regulating phosphorus in cotton production.